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Discussions and Knowledge Gaps

3

Denervation atrophy and rotator imbalance are each sufficient to produce the contracture in the rat. What is their relative contribution in a given child?

KNOWLEDGE GAP erb_two_sufficient_contracture_routes

Attached to

pathophysiology#Subscapularis Denervation Atrophy and Impaired Longitudinal Growth pathophysiology#Rotator Muscle Imbalance

Two selective-denervation experiments each produce the contracture on their own, and neither was designed to weigh them against the other. That is not an academic question, because the treatments act on different routes: botulinum toxin weakens the intact internal rotators and so targets imbalance, while therapy aimed at maintaining subscapularis length targets the atrophy route. Which one dominates in a particular child would predict which treatment helps them, and nothing measures it. One of the two papers raises the point itself.

Show evidence (1 reference)

PMID:25124991 SUPPORT INDIRECT Model Organism

"Our study shows that subscapularis denervation, per se, could explain shoulder contracture after neonatal brachial plexus injury, though its relevance compared to other pathogenic factors needs further investigation."

The authors state the open question directly: sufficiency is established, relative weight is not.

How much of the residual injury burden is preventable at all, given that most shoulder dystocia occurs without identifiable risk factors?

KNOWLEDGE GAP erb_prevention_ceiling

Attached to

environmental#Shoulder dystocia at delivery

Prevention here is obstetric, and it works: twelve years of multi-professional shoulder-dystocia simulation training was followed by a fall in brachial plexus injury from 7.4% to 1.3% of shoulder dystocia deliveries. But that is training in how to manage the event, not in how to avoid it. Risk-factor-based prevention has a hard ceiling, because half to two-thirds of shoulder dystocia happens in women with none of the recognised risk factors. Distinguishing the two kinds of prevention matters for what a service should invest in, and the literature does not separate their contributions.

Show evidence (2 references)

PMID:27318182 SUPPORT Human Clinical

"Its main risk factors are previous SD and macrosomia, but both are poorly predictive; 50-70% of SD cases occur in their absence, and most deliveries when they are present do not result in SD."

States the ceiling on risk-factor-based prediction in both directions, poor sensitivity and poor specificity.

PMID:25688719 SUPPORT Human Clinical

"MAIN OUTCOMES: Neonatal morbidity (brachial plexus injury, humeral fracture, clavicular fracture, 5-minute Apgar score <7) and documented management of shoulder dystocia (resolution manoeuvres performed, traction applied, head-to-body delivery interval)."

Records what the training study measured. It is an interrupted time series rather than a trial, so the fall in injury is a before-and-after association in one unit.

Does the rat glenoid deformity model the human one, given that the version change goes in the opposite direction?

HUMAN MODEL MISMATCH erb_rat_glenoid_direction_mismatch

Attached to

pathophysiology#Glenohumeral Dysplasia animal_models#Neonatal rat C5-C6 neurotomy model

The rat model reproduces the contracture faithfully and is the main evidence that the dysplasia is load-driven rather than primary. But its glenoid moves from retroversion to anteversion, whereas the human deformity is characterised by increasing retroversion with posterior subluxation. Quadrupedal shoulder loading is not bipedal shoulder loading, so the discrepancy is explicable, but it means the model supports the general claim that a growing glenoid remodels under sustained abnormal force and does not support the specific human deformity. This entry uses it for the former only, and the human dysplasia phenotype is evidenced from human data.

Show evidence (1 reference)

PMID:18343282 SUPPORT INDIRECT Model Organism

"Glenoid version changed from 2 degrees +/- 2 of retroversion (left side) to 8 degrees +/- 3 of anteversion."

The measurement whose direction differs from the human finding, which is the mismatch this discussion records.

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Pathophysiology

10

Excessive Lateral Traction on the Upper Brachial Plexus at Delivery

The initiating event. Increasing the head-to-shoulder angle during delivery, most often when the anterior shoulder is impacted behind the symphysis, stretches the upper brachial plexus. This is a mechanical lesion and there is no molecular initiating step above it.

Downstream

Graded Stretch Injury of the C5-C6 Upper Trunk The traction is transmitted to the C5-C6 roots and upper trunk, which are the most exposed part of the plexus in this delivery geometry.

Show evidence (1 reference)

PMID:39187951 SUPPORT Human Clinical

"Shoulder dystocia was the strongest risk factor for BPBI in the logistic regression model [adjusted odds ratio (AOR): 56.9, P <0.001]."

Quantifies the delivery circumstance that produces the traction, with an effect size large enough to make the mechanical account the default one.

Graded Stretch Injury of the C5-C6 Upper Trunk

The stretch produces a graded lesion along the Seddon spectrum: conduction block without axonal disruption at one end, axonal disruption within an intact sheath in the middle, rupture of the trunk, and root avulsion from the spinal cord at the other. The grade, not the fact of injury, is what determines everything downstream, and it is not directly measurable in the newborn.

brachial plexus UBERON:0001814

Downstream

Denervation of C5-C6 Innervated Shoulder and Elbow Muscles Axonal interruption disconnects the motor units of the muscles supplied by the upper trunk.

Show evidence (1 reference)

PMID:12874720 SUPPORT Human Clinical

"If spontaneous recovery does not occur within the first six months of life, investigations like electrophysiology, and CT-myelography and surgical exploration of the brachial plexus are recommended."

Records that the lesion grade is established only later, by investigation or exploration, which is why this node describes a graded injury rather than a specific one.

Denervation of C5-C6 Innervated Shoulder and Elbow Muscles

Loss of motor supply to deltoid, supraspinatus, infraspinatus, biceps, brachialis and subscapularis. The pattern of which muscles are denervated, and which are spared, is what generates the deformity rather than the total amount of weakness.

motor neuron CL:0000100 skeletal muscle fiber CL:0008002

skeletal muscle atrophy GO:0014732 ↑ INCREASED

Downstream

Upper limb muscle weakness Loss of motor supply to the upper-trunk muscles is what the flaccid weakness at birth is.

Shoulder girdle muscle atrophy Denervated muscle wastes, which is the observable counterpart of the denervation node.

Spontaneous Reinnervation and Functional Recovery In the large majority, the lesion is mild enough that the axons regenerate or conduction returns, and function is restored.

Subscapularis Denervation Atrophy and Impaired Longitudinal Growth Where reinnervation fails, the denervated subscapularis atrophies and does not grow in length as the limb grows.

Rotator Muscle Imbalance The external rotators are supplied by the upper trunk and the internal rotators only partly, so upper-trunk denervation shifts the balance of forces across the joint even when the subscapularis itself is spared.

Aberrant Reinnervation Through a Neuroma-in-Continuity Where the sheath is disrupted but continuity is maintained, regenerating axons can grow into the wrong distal pathways.

Show evidence (1 reference)

PMID:30020632 SUPPORT Other

"Erb palsy most commonly results from an upper brachial plexus birth injury involving the C5–C6 nerve roots, with occasional extension to C7, leading to flaccid weakness or paralysis of the affected upper extremity."

Names the denervation-driven weakness that defines this node.

Spontaneous Reinnervation and Functional Recovery

The dominant outcome, and the reason initial management is observation rather than surgery. Return of biceps function in the first months is the pivotal prognostic sign; its absence by three to six months is what converts observation into an operative decision.

neuron projection regeneration GO:0031102 ↑ INCREASED

Show evidence (2 references)

PMID:12874720 SUPPORT Human Clinical

"80 to 95% of these lesions recover spontaneously."

Quantifies the recovery branch.

PMID:25509702 SUPPORT Human Clinical

"OBJECTIVE: To document the natural history of brachial plexus birth palsy in relation to the recovery of elbow flexion and shoulder flexion in the first six months of life; to assess the outcome after microsurgery of the brachial plexus in patients who had no recovery of bicep function at six months."

Establishes the six-month biceps-recovery milestone as the natural-history landmark that operative decisions are keyed to.

Subscapularis Denervation Atrophy and Impaired Longitudinal Growth

The first of two independently sufficient routes to contracture. A denervated subscapularis loses mass and fibre size and, critically, fails to lengthen while the limb grows. The result is a relatively short, stiff internal rotator tethering the joint.

skeletal muscle atrophy GO:0014732 ↑ INCREASED

Animal models

Selective subscapularis denervation rat model Rat recapitulates Isolates one muscle's denervation as a sufficient cause of the contracture.

Downstream

Shoulder Internal Rotation Contracture Shown to be sufficient on its own: denervating the subscapularis alone produces the contracture in the rat model.

Show evidence (1 reference)

PMID:24388715 SUPPORT INDIRECT Model Organism

"BACKGROUND: An internal rotation contracture of the shoulder is common after neonatal brachial plexus injuries due to subscapularis shortening and atrophy."

States the shortening-and-atrophy account of the contracture that this node describes.

Rotator Muscle Imbalance

The second independently sufficient route. Denervating only the supraspinatus and infraspinatus, leaving the subscapularis intact and histologically normal, still produced the contracture. That result is what makes this a separate mechanism rather than a restatement of the atrophy one.

Animal models

Selective suprascapular neurectomy rat model Rat recapitulates Establishes imbalance as a second sufficient route, independent of subscapularis atrophy.

Downstream

Shoulder Internal Rotation Contracture Sufficient on its own, in a preparation where the subscapularis is spared.

Show evidence (1 reference)

PMID:24388715 SUPPORT INDIRECT Model Organism

"No differences were found in subscapularis muscle fiber size and area of fibrosis between shoulders after suprascapular nerve injury."

The control that makes this route independent: the subscapularis was histologically unchanged, so the contracture in that arm cannot be attributed to subscapularis atrophy.

Aberrant Reinnervation Through a Neuroma-in-Continuity

Regenerating axons crossing a neuroma-in-continuity are misrouted to antagonist muscles. The clinical consequence is cocontraction: agonist and antagonist fire together, so a child with an adequate passive range cannot use it. This is a disability produced by repair rather than by failure of repair, which is why it does not resolve with further waiting.

motor neuron CL:0000100

neuron projection regeneration GO:0031102 ↕ DYSREGULATED

Downstream

Persistent Functional Impairment of the Upper Limb Cocontraction limits usable motion independently of passive range.

Show evidence (1 reference)

PMID:38263956 SUPPORT INDIRECT Model Organism

"A number of these patients also suffer from cocontractions, preventing the use of an otherwise good passive range of motion in the shoulder."

Establishes cocontraction as a recognised component of the residual disability. Graded MODEL_ORGANISM: the claim is about patients but the publication is a juvenile-rat model study, and evidence_source classifies the publication.

Shoulder Internal Rotation Contracture

The convergence point of the two muscle routes, and the lesion that most subsequent treatment is aimed at. In the rat model every animal developed it within four weeks of the C5-C6 lesion, which is the consistency that two independently sufficient causes would predict.

shoulder joint UBERON:0016884

Animal models

Neonatal rat C5-C6 neurotomy model Rat recapitulates Every animal developed the contracture on a defined timescale after the lesion.

Downstream

Limited passive shoulder external rotation The contracture is measured as loss of passive external rotation.

Glenohumeral Dysplasia Sustained abnormal force across a growing joint remodels its shape. In the rat model, glenoid version moved from retroversion to anteversion with pseudoglenoid formation over the same interval.

Show evidence (1 reference)

PMID:18343282 SUPPORT INDIRECT Model Organism

"RESULTS: All animals developed shoulder internal rotation contracture within 4 weeks after the C5, C6 neurotomy."

Establishes the contracture as an obligate rather than occasional consequence of the lesion in the model, on a defined timescale.

Glenohumeral Dysplasia

Progressive deformity of the glenoid and humeral head with posterior subluxation, developing under the sustained abnormal forces of the contracture while the joint is still growing. Found in roughly half of permanent cases, and the reason surveillance of the shoulder continues after the nerve lesion has stopped changing.

chondrocyte CL:0000138

shoulder joint UBERON:0016884

Animal models

Neonatal rat C5-C6 neurotomy model Rat recapitulates Glenoid version shifted from retroversion to anteversion with pseudoglenoid formation, subluxation and humeral head deformity.

Downstream

Glenoid deformity with posterior humeral head subluxation The imaging and operative finding that the dysplasia node names.

Persistent Functional Impairment of the Upper Limb Once the joint surfaces are deformed, function is limited by joint geometry rather than by nerve or muscle, which is why secondary orthopaedic procedures rather than nerve surgery are what address it.

Show evidence (2 references)

PMID:37503533 SUPPORT Human Clinical

"Shoulder dysplasia was diagnosed in 49% of 270 patients with permanent brachial plexus birth injury in our catchment area from 1995 to 2021."

Gives the human frequency with its denominator and catchment, which is what makes it a population figure rather than a case-series impression.

PMID:37503533 SUPPORT Human Clinical

"The age at detection of shoulder dysplasia dropped from mean 5.4 years in children born before 2000 to mean 3.9 months in children born after 2009."

Shows that the age at which dysplasia is found is a property of surveillance practice rather than of the disease, which matters when reading older series.

Persistent Functional Impairment of the Upper Limb

The clinical endpoint in the minority who do not recover: a weak, internally rotated limb with limited abduction and external rotation, sometimes with elbow-flexion and forearm-supination deformity, and with usable motion further limited by cocontraction.

Downstream

Elbow flexion contracture A recognised sequela of the persisting impairment, established late enough that it is treated as a fixed deformity rather than as part of the initial palsy.

Show evidence (1 reference)

PMID:40958300 SUPPORT Human Clinical

"Functional recovery varied by surgical approach, with nerve grafts and transfers showing significant improvements in upper limb mobility and strength."

Establishes that the residual impairment is a mobility-and-strength deficit that intervention can move, which is what makes it the endpoint of this chain.

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Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.

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Phenotypes

5

Limbs 3

Upper limb muscle weakness VERY_FREQUENT HP:0003484

Show evidence (1 reference)

PMID:30020632 SUPPORT Other

"Erb palsy most commonly results from an upper brachial plexus birth injury involving the C5–C6 nerve roots, with occasional extension to C7, leading to flaccid weakness or paralysis of the affected upper extremity."

The defining clinical finding, stated with its anatomical basis.

Shoulder girdle muscle atrophy FREQUENT HP:0003724

Show evidence (1 reference)

PMID:24388715 SUPPORT INDIRECT Model Organism

"BACKGROUND: An internal rotation contracture of the shoulder is common after neonatal brachial plexus injuries due to subscapularis shortening and atrophy."

Names the atrophy component alongside the shortening.

Elbow flexion contracture HP:0002987

Show evidence (2 references)

PMID:42438048 SUPPORT Human Clinical

"BACKGROUND: Fixed flexion deformity (FFD) of the elbow is a recognized sequela of obstetric brachial plexus palsy (OBPP)."

States the phenotype and its relation to the disease directly. No frequency is given: this is a treated case series of 73 patients, which is a numerator without a denominator of all obstetric brachial plexus palsy, so the frequency slot is left empty rather than estimated from it.

PMID:42438048 SUPPORT Human Clinical

"Mean pretreatment active FFD was 45.8±19.9 degrees and improved to 20.7±15.1 degrees after treatment, giving a mean improvement of 25.2 degrees (95% CI: 21.6-28.8 degrees; P<0.001; Cohen dz=1.49)."

Quantifies the severity of the established deformity, which is what makes it a treated entity rather than a note in a follow-up list.

Musculoskeletal 2

Limited passive shoulder external rotation FREQUENT Joint contracture HP:0034392

Show evidence (1 reference)

PMID:24388715 SUPPORT INDIRECT Model Organism

"BACKGROUND: An internal rotation contracture of the shoulder is common after neonatal brachial plexus injuries due to subscapularis shortening and atrophy."

States that the contracture is a common consequence in humans; the sentence is the background framing of a rat study, so it is graded MODEL_ORGANISM in keeping with the publication it comes from rather than with the claim it makes.

Glenoid deformity with posterior humeral head subluxation FREQUENT Abnormal scapula morphology HP:0000782

Show evidence (1 reference)

PMID:37503533 SUPPORT Human Clinical

"Shoulder dysplasia was diagnosed in 49% of 270 patients with permanent brachial plexus birth injury in our catchment area from 1995 to 2021."

Gives the frequency among permanent cases, which is the denominator this FREQUENT band refers to.

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Medical Actions

4

Physical and Occupational Therapy

Action: physical therapy Ontology label: Physical Therapy NCIT:C15302

Platform: Behavioral / lifestyle

First-line and universal: maintaining passive range of motion while waiting to see whether the nerve recovers. It is directed at preventing the contracture rather than at the nerve lesion.

Mechanism Target:

Shoulder Internal Rotation Contracture — Aimed at the contracture, by maintaining length in the internal rotators through the period when the muscle is denervated and not growing.

Botulinum Toxin Injection of the Internal Rotators

Action: botulinum toxin chemodenervation Ontology label: Botulinum Toxin Therapy NCIT:C157775

Agent: botulinum toxin type A CHEBI:3160

Platform: Other

Chemical weakening of the internal rotators to rebalance the joint. The measured benefit outlasts the toxin's pharmacological half-life, which is the observation that makes it more than a temporising measure: gains of 46 degrees of passive external rotation at four months, with 18 degrees still present at eleven months.

Mechanism Target:

Rotator Muscle Imbalance — Acts directly on the imbalance route by weakening the relatively preserved internal rotators, rather than by strengthening the denervated external rotators.

Show evidence (1 reference)

PMID:32753228 SUPPORT Human Clinical

"Subjects demonstrated a significant increase in passive external rotation of 46° (range, 10° to 90) at 4 months; an average improvement of 18° (range, -30° to 80°) persisted at 11 months after injection."

Gives the effect size and its persistence beyond the toxin's half-life, which is what supports an effect on the underlying imbalance rather than a purely pharmacological one. Note the range crosses zero at eleven months, so some children lost ground.

Show evidence (1 reference)

PMID:32753228 SUPPORT Human Clinical

"Shoulder passive external rotation in adduction and Active Movement Scale external rotation scores were recorded before and after BTX-A injection."

Records what was measured. This is a retrospective before-and-after series, not a controlled trial, which is the main limit on how the effect size should be read.

Primary Nerve Reconstruction and Nerve Transfer

Action: nerve reconstruction and nerve transfer Ontology label: Surgical Procedure NCIT:C15329

Platform: Surgery

Neuroma excision with grafting, or distal nerve transfers, when biceps recovery has not occurred by around three to six months. Nerve transfers reported grade 4 or better elbow flexion in all evaluable patients in one series. A systematic review of the whole literature is more measured: grafts and transfers both improve function, and no approach is established as superior.

Mechanism Target:

Denervation of C5-C6 Innervated Shoulder and Elbow Muscles — The only treatment aimed at the nerve lesion itself, restoring axonal continuity to the denervated muscles before the downstream deformity is established.

Show evidence (1 reference)

PMID:27543083 SUPPORT Human Clinical

"Of the remainder, 11 had grade 4+ power of elbow flexion and six patients had grade 4 power at 1 year follow-up; all had 4+ power of elbow flexion at final follow-up."

Reports the reinnervation outcome for the target muscle. A small uncontrolled series in a selected injury grade, so it establishes that the approach can work rather than how it compares.

Show evidence (1 reference)

PMID:40958300 SUPPORT Human Clinical

"While nerve grafts and nerve transfers show promising results, there is no definitive consensus on their superiority, particularly regarding external shoulder rotation and hand function recovery."

The systematic review's own hedge, which is the honest summary of the comparative evidence and is deliberately quoted rather than the single-series result above.

Secondary Shoulder Reconstruction

Action: orthopedic surgical procedure Ontology label: Orthopedic Surgical Procedure NCIT:C16186

Platform: Surgery

Procedures for established deformity: anterior shoulder and subscapularis release, tendon transfer, and humeral derotation osteotomy. Anterior release improved glenoid version from -32 to -12 degrees, and open subscapularis lengthening with joint relocation gave durable remodelling at ten years, so the deformed joint retains remodelling capacity if the abnormal force is removed.

Mechanism Target:

Glenohumeral Dysplasia — Removes the deforming force and relocates the joint, after which the growing glenoid remodels. This is the therapeutic counterpart of the claim that the dysplasia is generated by sustained abnormal load rather than being a fixed primary malformation.

Show evidence (2 references)

PMID:30981548 SUPPORT Human Clinical

"RESULTS: After a mean follow-up period of 23 months, glenoid version and the percentage of the humeral head anterior to the middle of the glenoid fossa significantly improved from -32° and 18%, respectively, to mean postoperative values of -12° (P < .001) and 45% (P < .001), respectively."

Measures the bony remodelling after release on two axes, version and humeral head position, which is what supports the claim that the deformity is load-driven and partly reversible.

PMID:31085034 SUPPORT Human Clinical

"The glenoid retroversion changed by 14.8° (95% confidence interval, 11.1°-18.4°; P < .01), from 25.4° to 10.6°, approaching a normal value."

The same remodelling measured at a mean of 10.2 years, so the correction is durable rather than an early postoperative appearance. Note this is a before-and-after study without a control arm.

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Environmental Factors

3

Shoulder dystocia at delivery

No exposure_term is bound. ECTO is an ontology of chemical, dietary, social and physical environmental exposures; it has no concept for an intrapartum mechanical event of this kind, and binding a generic physical-force term would assert something less specific than the free text already says. HP:0011413 Shoulder dystocia exists as a phenotype term but describes the mother's delivery rather than an exposure of the infant, so it is not used here either.

Impaction of the anterior shoulder behind the pubic symphysis, requiring resolution manoeuvres. It is by a wide margin the strongest risk factor, and it is also the circumstance in which the traction that injures the plexus is applied.

Show evidence (1 reference)

PMID:41367186 SUPPORT Human Clinical

"INTRODUCTION: Brachial plexus injury (BPI) is one of the major complications associated with shoulder dystocia."

Establishes the exposure-outcome pairing that this environmental entry records.

Mechanism Target:

TRIGGERS Excessive Lateral Traction on the Upper Brachial Plexus at Delivery — Shoulder dystocia is the delivery geometry in which the head-to-shoulder angle is forced open, which is the mechanical event that stretches the plexus.

Show evidence (1 reference)

PMID:39187951 SUPPORT Human Clinical

"Shoulder dystocia was the strongest risk factor for BPBI in the logistic regression model [adjusted odds ratio (AOR): 56.9, P <0.001]."

Gives the adjusted effect size for the association between the exposure and the injury.

Cesarean delivery

No exposure_term is bound, for the same reason as the shoulder dystocia entry: ECTO has no concept for a mode of delivery. NCIT:C46088 (Cesarean Section) exists but is a procedure term rather than an exposure, and this record describes the infant's exposure rather than the mother's operation.

Protective rather than causative, and the only intervention with a measured effect on incidence. Delivery by cesarean section removes the geometry in which the traction is applied. The protection is largest where the risk is largest: in macrosomic newborns the adjusted odds ratio was 0.581, below the 1.000 reference for a normal-weight newborn delivered vaginally.

Show evidence (1 reference)

PMID:39187951 SUPPORT Human Clinical

"The AOR for a newborn with macrosomia born through C-section (AOR: 0.581, 95% CI: 0.365-0.925) was lower than that for a normal weight newborn born vaginally (AOR: 1.000, P =0.022)."

Gives the adjusted effect size with its confidence interval and the comparator it is measured against.

Mechanism Target:

PROTECTS_AGAINST Excessive Lateral Traction on the Upper Brachial Plexus at Delivery — Acts on the initiating mechanical event by avoiding the vaginal delivery in which the head-to-shoulder angle is forced open.

Show evidence (1 reference)

PMID:39187951 SUPPORT Human Clinical

"Stratified analysis indicated C-section delivery was protective against BPBI across newborn weight classes, but the magnitude of this protective value was highest among newborns with macrosomia."

Reports the protective effect and, importantly, that it is not uniform: it is strongest in the group at highest risk, which is what a mechanical account predicts.

Fetal macrosomia

No exposure_term is bound. ECTO covers environmental exposures of the organism, not fetal growth status, and HP:0001520 (Large for gestational age) describes the infant rather than an exposure acting on it.

The upstream risk factor that makes the impaction likely, and the one that maternal diabetes and obesity act through. It is recorded here as a predisposing exposure rather than a trigger: macrosomia does not itself apply traction, it raises the probability that the shoulder impacts.

Show evidence (1 reference)

PMID:39187951 SUPPORT Human Clinical

"An interaction between cesarean (C-) section and newborn weight was explored by defining BPBI rates in a stratified manner."

Establishes newborn weight as an effect modifier of the injury rate, which is the basis for curating macrosomia as a separate exposure.

Mechanism Target:

PREDISPOSES Excessive Lateral Traction on the Upper Brachial Plexus at Delivery — Acts through shoulder dystocia rather than directly. The known intermediate is the impaction itself, which is modeled as its own environmental entry above.

Show evidence (1 reference)

PMID:27318182 SUPPORT Human Clinical

"Its main risk factors are previous SD and macrosomia, but both are poorly predictive; 50-70% of SD cases occur in their absence, and most deliveries when they are present do not result in SD."

Names macrosomia as a main risk factor and, in the same sentence, states how poorly it predicts, which is why this link is PREDISPOSES rather than TRIGGERS.

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Diagnosis

2

Clinical examination at birth with serial motor assessment (PRESENT)

Diagnosis is clinical: a flaccid arm at birth in the characteristic posture. What matters afterwards is serial assessment, because the decision that changes outcome is whether biceps function returns in the first months, and that is a longitudinal observation rather than a single test.

Show evidence (1 reference)

PMID:25509702 SUPPORT Human Clinical

"OBJECTIVE: To document the natural history of brachial plexus birth palsy in relation to the recovery of elbow flexion and shoulder flexion in the first six months of life; to assess the outcome after microsurgery of the brachial plexus in patients who had no recovery of bicep function at six months."

Frames the diagnostic task as serial assessment of recovery against the six-month biceps milestone.

Imaging and electrophysiology for lesion grade (PRESENT)

Reserved for infants who are not recovering. The question these answer is not whether there is an injury but what grade it is, and specifically whether roots have been avulsed, which cannot be repaired by grafting.

Show evidence (2 references)

PMID:12874720 SUPPORT Human Clinical

"If spontaneous recovery does not occur within the first six months of life, investigations like electrophysiology, and CT-myelography and surgical exploration of the brachial plexus are recommended."

States both the trigger for investigation and the modalities, and makes clear they follow rather than establish the diagnosis.

PMID:39432686 SUPPORT Human Clinical

"The mean sensitivity and mean specificity of MRI for detecting root avulsion was 68% (95% CI: 55%, 79%) and 89% (95% CI: 78%, 95%), respectively."

Puts numbers on how much the imaging answers. A sensitivity of 68 per cent means a negative MRI does not exclude avulsion, which is why imaging informs the operative decision rather than making it.

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Prevalence

1

Germany, 2005-2018, national hospital discharge data

Annual Incidence 15.0 per 100,000 live births 1–9 per 100,000 per year

Reported as 0.15 per 1000 live births in 2018, down from 0.28 in 2005; normalized here to 15 per 100,000 live births. The rate is falling, and the source pairs the decline with rising cesarean delivery rates. This is obstetric brachial plexus injury overall rather than the Erb subtype specifically, so it is an upper bound on the Erb-specific rate. Note also that published incidence figures for this condition vary by roughly an order of magnitude across countries and ascertainment methods, so a single national figure should not be read as the worldwide rate.

Show evidence (2 references)

PMID:40315612 SUPPORT Human Clinical

"The incidence of OBPI per 1000 live births significantly decreased by 47.57%, from 0.28 in 2005 to 0.15 in 2018 (p < 0.001), representing a mean annual decrease of 0.010 ± 0.026."

Gives the rate and its denominator, and the trend that the normalized figure is taken from.

PMID:40315612 SUPPORT Human Clinical

"CONCLUSIONS: OBPI is a rare disease, with a decreasing incidence paralleled by an increase in cesarean birth delivery rates between 2005 and 2018 in Germany."

Names the population and period the rate applies to, and the cesarean-rate association the authors pair it with.

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Differential Diagnoses

1

Conditions with similar clinical presentations that must be differentiated from Erb Palsy:

Clavicle fracture

Overlapping Features The other common birth injury of the same delivery, and the main early mimic: a newborn with a fractured clavicle also does not move the arm, from pain rather than from denervation. They share risk factors and can co-occur.

Show evidence (1 reference)

PMID:42486682 SUPPORT Human Clinical

"OBJECTIVE: Clavicle fracture is the most common birth-related fracture, resulting in concerns and dissatisfaction, while brachial plexus birth injury (BPBI) is a severe complication with potential lifelong sequelae."

Establishes the two as the paired birth injuries of the same event, which is what makes clavicle fracture the differential rather than an unrelated condition.

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Animal Models

3

Neonatal rat C5-C6 neurotomy model

The workhorse model for the post-injury deformity. Sectioning C5-C6 in the newborn rat reproduces the internal rotation contracture in every animal within four weeks and goes on to reproduce the glenoid deformity, which is what makes it a model of the sequelae rather than only of the nerve lesion.

Species

Rat

Genotype

Wild type, surgical C5-C6 neurotomy at postnatal day 5

Publication

PMID:18343282

Pathograph links

Shoulder Internal Rotation Contracture recapitulates fidelity: high observes: tissue Every animal developed the contracture on a defined timescale after the lesion.

Limitations: The lesion is a clean surgical neurotomy of known grade, whereas the human injury is a traction lesion of unknown and variable grade. The model therefore reproduces what happens after a severe lesion, and says nothing about the graded severity that determines which human infants reach this branch at all.

Readouts

Shoulder internal rotation contracture at 4 weeks

Direction: INCREASED

Interpretation: Presence of the contracture in every operated animal within 4 weeks.

Show evidence (1 reference)

PMID:18343282 SUPPORT INDIRECT Model Organism

"RESULTS: All animals developed shoulder internal rotation contracture within 4 weeks after the C5, C6 neurotomy."

The measurement behind this readout, with its timescale and completeness.

Show evidence (1 reference)

PMID:18343282 SUPPORT INDIRECT Model Organism

"CONCLUSIONS: This neonatal rat model clearly demonstrated typical shoulder deformities similar to that resulting from Erb's palsy."

The authors' own claim that the model reproduces the human deformities, which is what licenses treating it as informative for this node.

Glenohumeral Dysplasia recapitulates fidelity: moderate observes: tissue Glenoid version shifted from retroversion to anteversion with pseudoglenoid formation, subluxation and humeral head deformity.

Limitations: The direction of the version change is not the same as in humans, where the characteristic finding is increased glenoid retroversion with posterior subluxation. The model reproduces that a growing glenoid remodels under abnormal load, not the specific human deformity, and this entry does not use it to support the human dysplasia phenotype.

Readouts

Glenoid version

Direction: ALTERED

Interpretation: Measured shift in glenoid version, the bony correlate of the dysplasia node.

Show evidence (1 reference)

PMID:18343282 SUPPORT INDIRECT Model Organism

"Glenoid version changed from 2 degrees +/- 2 of retroversion (left side) to 8 degrees +/- 3 of anteversion."

The quantitative readout, with its direction and dispersion.

Show evidence (1 reference)

PMID:18343282 SUPPORT INDIRECT Model Organism

"Both shoulders were harvested, decalcified, and transected in the axial plane for glenoid version measurement and shoulder histology."

Records how the deformity was measured, which is what makes the version figure interpretable.

Selective subscapularis denervation rat model

The dissection experiment for the atrophy route. Denervating the subscapularis alone produced the contracture, establishing that route as sufficient.

Species

Rat

Genotype

Wild type, selective subscapularis denervation

Publication

PMID:25124991

Pathograph links

Subscapularis Denervation Atrophy and Impaired Longitudinal Growth recapitulates fidelity: moderate observes: tissue Isolates one muscle's denervation as a sufficient cause of the contracture.

Limitations: Selective single-muscle denervation does not occur in the human injury, where the upper trunk supplies several muscles at once. The experiment establishes sufficiency in principle; it cannot say how much of a given child's contracture this route contributes, and the authors say so.

Show evidence (1 reference)

PMID:25124991 SUPPORT INDIRECT Model Organism

"Our study shows that subscapularis denervation, per se, could explain shoulder contracture after neonatal brachial plexus injury, though its relevance compared to other pathogenic factors needs further investigation."

The sufficiency result together with the authors' explicit limitation, which is the basis for MODERATE rather than HIGH fidelity here.

Selective suprascapular neurectomy rat model

The complementary dissection experiment. Denervating only the external rotators, with the subscapularis intact and histologically unchanged, still produced the contracture.

Species

Rat

Genotype

Wild type, selective suprascapular neurectomy with subscapularis spared

Publication

PMID:24388715

Pathograph links

Rotator Muscle Imbalance recapitulates fidelity: moderate observes: tissue Establishes imbalance as a second sufficient route, independent of subscapularis atrophy.

Limitations: As with the subscapularis experiment, the lesion is selective in a way the human injury is not. What the pair of experiments establishes is that two routes are each sufficient, not their relative contribution in any patient.

Readouts

Subscapularis fibre size and fibrosis

Direction: UNCHANGED

Interpretation: A negative result, and the load-bearing one: the spared subscapularis was histologically normal, so the contracture in this arm cannot be attributed to it.

Show evidence (1 reference)

PMID:24388715 SUPPORT INDIRECT Model Organism

"No differences were found in subscapularis muscle fiber size and area of fibrosis between shoulders after suprascapular nerve injury."

The measurement showing the spared muscle was unaffected.

Show evidence (1 reference)

PMID:24388715 SUPPORT INDIRECT Model Organism

"CONCLUSIONS: Our study supports the theory that shoulder muscle imbalance is a cause of shoulder contracture in patients with neonatal brachial plexus palsy."

The conclusion this model link records.

{ }

Source YAML

click to show

name: Erb Palsy
creation_date: "2026-09-07T18:40:00Z"
category: Acquired
synonyms:
- Erb-Duchenne paralysis
- Erb-Duchenne palsy
- upper brachial plexus birth injury
- C5-C6 brachial plexus birth palsy
description: >-
  Erb palsy is the upper-trunk form of brachial plexus birth injury: traction on the
  C5-C6 roots during delivery, most often when the shoulder is impacted, producing
  flaccid weakness of the shoulder and elbow with the arm held adducted, internally
  rotated and pronated.

  It is worth curating as a mechanism rather than as a birth complication because the
  interesting part is what happens after the nerve heals. Most infants recover
  spontaneously. In the minority who do not, the residual disability is not simply
  persistent weakness: it is a progressive musculoskeletal deformity generated by the
  denervation, in a joint that is still growing. Neonatal rat work has separated two
  sufficient causes of the internal-rotation contracture that follows. Denervating the
  subscapularis alone produces it, through atrophy and impaired longitudinal growth of
  that muscle. Denervating only the external rotators and sparing the subscapularis
  also produces it, through imbalance. Either route alone is enough, which is why the
  contracture is so consistent, and it is also why a treatment aimed at only one of
  them is incomplete. The contracture then remodels the growing glenohumeral joint into
  dysplasia, found in roughly half of permanent cases.

  A third strand of residual disability comes from repair rather than from loss:
  regenerating axons crossing a neuroma-in-continuity reach antagonist muscles, so the
  child co-contracts and cannot use a passive range of motion that is otherwise
  adequate.

  Prevention is obstetric and its ceiling is known: shoulder dystocia is by far the
  strongest risk factor, but half to two-thirds of shoulder dystocia occurs with no
  identifiable risk factor present.
disease_term:
  preferred_term: Erb palsy
  term:
    id: MONDO:0700303
    label: Erb palsy
parents:
- Brachial plexus neuropathy from injury
- Palsy
prevalence:
- population: Germany, 2005-2018, national hospital discharge data
  measure_type: ANNUAL_INCIDENCE
  prevalence_class: BAND_1_9_PER_100000
  rate_per_100000: 15.0
  rate_denominator: LIVE_BIRTHS
  notes: >-
    Reported as 0.15 per 1000 live births in 2018, down from 0.28 in 2005; normalized
    here to 15 per 100,000 live births. The rate is falling, and the source pairs the
    decline with rising cesarean delivery rates. This is obstetric brachial plexus
    injury overall rather than the Erb subtype specifically, so it is an upper bound on
    the Erb-specific rate. Note also that published incidence figures for this condition
    vary by roughly an order of magnitude across countries and ascertainment methods,
    so a single national figure should not be read as the worldwide rate.
  evidence:
  - reference: PMID:40315612
    reference_title: "Epidemiology and surgical management of obstetric brachial plexus injury: a national cohort study."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The incidence of OBPI per 1000 live births significantly decreased by 47.57%, from 0.28 in 2005 to 0.15 in 2018 (p < 0.001), representing a mean annual decrease of 0.010 ± 0.026."
    explanation: >-
      Gives the rate and its denominator, and the trend that the normalized figure is
      taken from.
  - reference: PMID:40315612
    reference_title: "Epidemiology and surgical management of obstetric brachial plexus injury: a national cohort study."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "CONCLUSIONS: OBPI is a rare disease, with a decreasing incidence paralleled by an increase in cesarean birth delivery rates between 2005 and 2018 in Germany."
    explanation: >-
      Names the population and period the rate applies to, and the cesarean-rate
      association the authors pair it with.
pathophysiology:
- name: Excessive Lateral Traction on the Upper Brachial Plexus at Delivery
  biological_scale: ORGANISM
  description: >-
    The initiating event. Increasing the head-to-shoulder angle during delivery, most
    often when the anterior shoulder is impacted behind the symphysis, stretches the
    upper brachial plexus. This is a mechanical lesion and there is no molecular
    initiating step above it.
  downstream:
  - target: Graded Stretch Injury of the C5-C6 Upper Trunk
    causal_link_type: DIRECT
    description: >-
      The traction is transmitted to the C5-C6 roots and upper trunk, which are the most
      exposed part of the plexus in this delivery geometry.
    evidence:
    - reference: PMID:30020632
      reference_title: "Erb Palsy."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "Erb palsy most commonly results from an upper brachial plexus birth injury involving the C5–C6 nerve roots, with occasional extension to C7, leading to flaccid weakness or paralysis of the affected upper extremity."
      explanation: >-
        Names the injured roots and the resulting deficit, which is the step this edge
        asserts. Graded OTHER as a clinical reference chapter rather than a study.
  evidence:
  - reference: PMID:39187951
    reference_title: "Epidemiology of Brachial Plexus Birth Injury and the Impact of Cesarean Section on Its Incidence."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Shoulder dystocia was the strongest risk factor for BPBI in the logistic regression model [adjusted odds ratio (AOR): 56.9, P <0.001]."
    explanation: >-
      Quantifies the delivery circumstance that produces the traction, with an effect
      size large enough to make the mechanical account the default one.
- name: Graded Stretch Injury of the C5-C6 Upper Trunk
  biological_scale: TISSUE
  description: >-
    The stretch produces a graded lesion along the Seddon spectrum: conduction block
    without axonal disruption at one end, axonal disruption within an intact sheath in
    the middle, rupture of the trunk, and root avulsion from the spinal cord at the
    other. The grade, not the fact of injury, is what determines everything downstream,
    and it is not directly measurable in the newborn.
  locations:
  - preferred_term: brachial plexus
    term:
      id: UBERON:0001814
      label: brachial nerve plexus
  downstream:
  - target: Denervation of C5-C6 Innervated Shoulder and Elbow Muscles
    causal_link_type: DIRECT
    description: >-
      Axonal interruption disconnects the motor units of the muscles supplied by the
      upper trunk.
    evidence:
    - reference: PMID:30020632
      reference_title: "Erb Palsy."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "Erb palsy most commonly results from an upper brachial plexus birth injury involving the C5–C6 nerve roots, with occasional extension to C7, leading to flaccid weakness or paralysis of the affected upper extremity."
      explanation: >-
        States the nerve-to-weakness step. The flaccidity is the clinical signature of
        denervation rather than of a central lesion.
  evidence:
  - reference: PMID:12874720
    reference_title: "[Management of obstetrical brachial plexus palsy--own experience with the primary operative technique]."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "If spontaneous recovery does not occur within the first six months of life, investigations like electrophysiology, and CT-myelography and surgical exploration of the brachial plexus are recommended."
    explanation: >-
      Records that the lesion grade is established only later, by investigation or
      exploration, which is why this node describes a graded injury rather than a
      specific one.
- name: Denervation of C5-C6 Innervated Shoulder and Elbow Muscles
  biological_scale: TISSUE
  description: >-
    Loss of motor supply to deltoid, supraspinatus, infraspinatus, biceps, brachialis
    and subscapularis. The pattern of which muscles are denervated, and which are
    spared, is what generates the deformity rather than the total amount of weakness.
  cell_types:
  - preferred_term: motor neuron
    term:
      id: CL:0000100
      label: motor neuron
  - preferred_term: skeletal muscle fiber
    term:
      id: CL:0008002
      label: skeletal muscle fiber
  biological_processes:
  - preferred_term: skeletal muscle atrophy
    term:
      id: GO:0014732
      label: skeletal muscle atrophy
    modifier: INCREASED
  downstream:
  - target: Upper limb muscle weakness
    causal_link_type: DIRECT
    description: >-
      Loss of motor supply to the upper-trunk muscles is what the flaccid weakness at
      birth is.
  - target: Shoulder girdle muscle atrophy
    causal_link_type: DIRECT
    description: >-
      Denervated muscle wastes, which is the observable counterpart of the denervation
      node.
  - target: Spontaneous Reinnervation and Functional Recovery
    causal_link_type: DIRECT
    description: >-
      In the large majority, the lesion is mild enough that the axons regenerate or
      conduction returns, and function is restored.
    evidence:
    - reference: PMID:12874720
      reference_title: "[Management of obstetrical brachial plexus palsy--own experience with the primary operative technique]."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "80 to 95% of these lesions recover spontaneously."
      explanation: >-
        Gives the size of the recovery branch, which is what makes this the dominant
        outcome rather than an alternative one.
  - target: Subscapularis Denervation Atrophy and Impaired Longitudinal Growth
    causal_link_type: DIRECT
    description: >-
      Where reinnervation fails, the denervated subscapularis atrophies and does not
      grow in length as the limb grows.
    evidence:
    - reference: PMID:25124991
      reference_title: "The role of subscapularis muscle denervation in the pathogenesis of shoulder internal rotation contracture after neonatal brachial plexus palsy: a study in a rat model."
      supports: SUPPORT
      directness: INDIRECT
      evidence_source: MODEL_ORGANISM
      snippet: "Our study shows that subscapularis denervation, per se, could explain shoulder contracture after neonatal brachial plexus injury, though its relevance compared to other pathogenic factors needs further investigation."
      explanation: >-
        Establishes subscapularis denervation as sufficient for the downstream
        contracture. Graded INDIRECT: this is a rat experiment, and the authors
        themselves qualify how much of the human pathogenesis it accounts for.
  - target: Rotator Muscle Imbalance
    causal_link_type: DIRECT
    description: >-
      The external rotators are supplied by the upper trunk and the internal rotators
      only partly, so upper-trunk denervation shifts the balance of forces across the
      joint even when the subscapularis itself is spared.
    evidence:
    - reference: PMID:24388715
      reference_title: "The role of muscle imbalance in the pathogenesis of shoulder contracture after neonatal brachial plexus palsy: a study in a rat model."
      supports: SUPPORT
      directness: INDIRECT
      evidence_source: MODEL_ORGANISM
      snippet: "MATERIALS AND METHODS: We performed selective neurectomy of the suprascapular nerve in 15 newborn rats to denervate only the supraspinatus and the infraspinatus muscles, leaving the subscapularis muscle intact."
      explanation: >-
        Describes the experiment that isolates the imbalance route by denervating only
        the external rotators. Graded INDIRECT as a rat model of the human lesion.
  - target: Aberrant Reinnervation Through a Neuroma-in-Continuity
    causal_link_type: DIRECT
    description: >-
      Where the sheath is disrupted but continuity is maintained, regenerating axons can
      grow into the wrong distal pathways.
  evidence:
  - reference: PMID:30020632
    reference_title: "Erb Palsy."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Erb palsy most commonly results from an upper brachial plexus birth injury involving the C5–C6 nerve roots, with occasional extension to C7, leading to flaccid weakness or paralysis of the affected upper extremity."
    explanation: >-
      Names the denervation-driven weakness that defines this node.
- name: Spontaneous Reinnervation and Functional Recovery
  biological_scale: ORGANISM
  description: >-
    The dominant outcome, and the reason initial management is observation rather than
    surgery. Return of biceps function in the first months is the pivotal prognostic
    sign; its absence by three to six months is what converts observation into an
    operative decision.
  biological_processes:
  - preferred_term: neuron projection regeneration
    term:
      id: GO:0031102
      label: neuron projection regeneration
    modifier: INCREASED
  evidence:
  - reference: PMID:12874720
    reference_title: "[Management of obstetrical brachial plexus palsy--own experience with the primary operative technique]."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "80 to 95% of these lesions recover spontaneously."
    explanation: Quantifies the recovery branch.
  - reference: PMID:25509702
    reference_title: "Brachial plexus birth palsy: the natural history, outcome of microsurgical repair and operative reconstruction."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "OBJECTIVE: To document the natural history of brachial plexus birth palsy in relation to the recovery of elbow flexion and shoulder flexion in the first six months of life; to assess the outcome after microsurgery of the brachial plexus in patients who had no recovery of bicep function at six months."
    explanation: >-
      Establishes the six-month biceps-recovery milestone as the natural-history
      landmark that operative decisions are keyed to.
- name: Subscapularis Denervation Atrophy and Impaired Longitudinal Growth
  biological_scale: TISSUE
  description: >-
    The first of two independently sufficient routes to contracture. A denervated
    subscapularis loses mass and fibre size and, critically, fails to lengthen while the
    limb grows. The result is a relatively short, stiff internal rotator tethering the
    joint.
  biological_processes:
  - preferred_term: skeletal muscle atrophy
    term:
      id: GO:0014732
      label: skeletal muscle atrophy
    modifier: INCREASED
  downstream:
  - target: Shoulder Internal Rotation Contracture
    causal_link_type: DIRECT
    description: >-
      Shown to be sufficient on its own: denervating the subscapularis alone produces
      the contracture in the rat model.
    evidence:
    - reference: PMID:25124991
      reference_title: "The role of subscapularis muscle denervation in the pathogenesis of shoulder internal rotation contracture after neonatal brachial plexus palsy: a study in a rat model."
      supports: SUPPORT
      directness: INDIRECT
      evidence_source: MODEL_ORGANISM
      snippet: "Our study shows that subscapularis denervation, per se, could explain shoulder contracture after neonatal brachial plexus injury, though its relevance compared to other pathogenic factors needs further investigation."
      explanation: >-
        The sufficiency claim this edge rests on, with the authors' own caveat about its
        weight relative to other routes.
  evidence:
  - reference: PMID:24388715
    reference_title: "The role of muscle imbalance in the pathogenesis of shoulder contracture after neonatal brachial plexus palsy: a study in a rat model."
    supports: SUPPORT
    directness: INDIRECT
    evidence_source: MODEL_ORGANISM
    snippet: "BACKGROUND: An internal rotation contracture of the shoulder is common after neonatal brachial plexus injuries due to subscapularis shortening and atrophy."
    explanation: >-
      States the shortening-and-atrophy account of the contracture that this node
      describes.
- name: Rotator Muscle Imbalance
  biological_scale: TISSUE
  description: >-
    The second independently sufficient route. Denervating only the supraspinatus and
    infraspinatus, leaving the subscapularis intact and histologically normal, still
    produced the contracture. That result is what makes this a separate mechanism rather
    than a restatement of the atrophy one.
  downstream:
  - target: Shoulder Internal Rotation Contracture
    causal_link_type: DIRECT
    description: >-
      Sufficient on its own, in a preparation where the subscapularis is spared.
    evidence:
    - reference: PMID:24388715
      reference_title: "The role of muscle imbalance in the pathogenesis of shoulder contracture after neonatal brachial plexus palsy: a study in a rat model."
      supports: SUPPORT
      directness: INDIRECT
      evidence_source: MODEL_ORGANISM
      snippet: "CONCLUSIONS: Our study supports the theory that shoulder muscle imbalance is a cause of shoulder contracture in patients with neonatal brachial plexus palsy."
      explanation: >-
        The authors' conclusion, which is the causal claim this edge makes. Graded
        INDIRECT as a rat result generalized to the human condition.
  evidence:
  - reference: PMID:24388715
    reference_title: "The role of muscle imbalance in the pathogenesis of shoulder contracture after neonatal brachial plexus palsy: a study in a rat model."
    supports: SUPPORT
    directness: INDIRECT
    evidence_source: MODEL_ORGANISM
    snippet: "No differences were found in subscapularis muscle fiber size and area of fibrosis between shoulders after suprascapular nerve injury."
    explanation: >-
      The control that makes this route independent: the subscapularis was
      histologically unchanged, so the contracture in that arm cannot be attributed to
      subscapularis atrophy.
- name: Aberrant Reinnervation Through a Neuroma-in-Continuity
  biological_scale: CELLULAR
  description: >-
    Regenerating axons crossing a neuroma-in-continuity are misrouted to antagonist
    muscles. The clinical consequence is cocontraction: agonist and antagonist fire
    together, so a child with an adequate passive range cannot use it. This is a
    disability produced by repair rather than by failure of repair, which is why it does
    not resolve with further waiting.
  cell_types:
  - preferred_term: motor neuron
    term:
      id: CL:0000100
      label: motor neuron
  biological_processes:
  - preferred_term: neuron projection regeneration
    term:
      id: GO:0031102
      label: neuron projection regeneration
    modifier: DYSREGULATED
  downstream:
  - target: Persistent Functional Impairment of the Upper Limb
    causal_link_type: DIRECT
    description: >-
      Cocontraction limits usable motion independently of passive range.
    evidence:
    - reference: PMID:38263956
      reference_title: "Nerve Tracing in Juvenile Rats: A Feasible Model for the Study of Brachial Plexus Birth Palsy and Cocontractions?"
      supports: SUPPORT
      directness: INDIRECT
      evidence_source: MODEL_ORGANISM
      snippet: "A number of these patients also suffer from cocontractions, preventing the use of an otherwise good passive range of motion in the shoulder."
      explanation: >-
        States precisely the dissociation this edge asserts, between passive range and
        usable function. Graded MODEL_ORGANISM because the sentence is the background
        framing of a juvenile-rat study, in keeping with the publication it comes from
        rather than with the claim it makes, and INDIRECT for the same reason.
  evidence:
  - reference: PMID:38263956
    reference_title: "Nerve Tracing in Juvenile Rats: A Feasible Model for the Study of Brachial Plexus Birth Palsy and Cocontractions?"
    supports: SUPPORT
    directness: INDIRECT
    evidence_source: MODEL_ORGANISM
    snippet: "A number of these patients also suffer from cocontractions, preventing the use of an otherwise good passive range of motion in the shoulder."
    explanation: >-
      Establishes cocontraction as a recognised component of the residual disability.
      Graded MODEL_ORGANISM: the claim is about patients but the publication is a
      juvenile-rat model study, and evidence_source classifies the publication.
- name: Shoulder Internal Rotation Contracture
  biological_scale: TISSUE
  description: >-
    The convergence point of the two muscle routes, and the lesion that most subsequent
    treatment is aimed at. In the rat model every animal developed it within four weeks
    of the C5-C6 lesion, which is the consistency that two independently sufficient
    causes would predict.
  locations:
  - preferred_term: shoulder joint
    term:
      id: UBERON:0016884
      label: shoulder joint
  downstream:
  - target: Limited passive shoulder external rotation
    causal_link_type: DIRECT
    description: >-
      The contracture is measured as loss of passive external rotation.
  - target: Glenohumeral Dysplasia
    causal_link_type: DIRECT
    description: >-
      Sustained abnormal force across a growing joint remodels its shape. In the rat
      model, glenoid version moved from retroversion to anteversion with pseudoglenoid
      formation over the same interval.
    evidence:
    - reference: PMID:18343282
      reference_title: "Brachial plexus birth palsy-associated shoulder deformity: a rat model study."
      supports: SUPPORT
      directness: INDIRECT
      evidence_source: MODEL_ORGANISM
      snippet: "Glenoid version changed from 2 degrees +/- 2 of retroversion (left side) to 8 degrees +/- 3 of anteversion."
      explanation: >-
        Measures the bony remodelling that follows the contracture in the model. Graded
        INDIRECT: the human counterpart is observed cross-sectionally rather than
        followed from contracture to deformity in the same subjects.
  evidence:
  - reference: PMID:18343282
    reference_title: "Brachial plexus birth palsy-associated shoulder deformity: a rat model study."
    supports: SUPPORT
    directness: INDIRECT
    evidence_source: MODEL_ORGANISM
    snippet: "RESULTS: All animals developed shoulder internal rotation contracture within 4 weeks after the C5, C6 neurotomy."
    explanation: >-
      Establishes the contracture as an obligate rather than occasional consequence of
      the lesion in the model, on a defined timescale.
- name: Glenohumeral Dysplasia
  biological_scale: TISSUE
  description: >-
    Progressive deformity of the glenoid and humeral head with posterior subluxation,
    developing under the sustained abnormal forces of the contracture while the joint is
    still growing. Found in roughly half of permanent cases, and the reason surveillance
    of the shoulder continues after the nerve lesion has stopped changing.
  locations:
  - preferred_term: shoulder joint
    term:
      id: UBERON:0016884
      label: shoulder joint
  cell_types:
  - preferred_term: chondrocyte
    term:
      id: CL:0000138
      label: chondrocyte
  downstream:
  - target: Glenoid deformity with posterior humeral head subluxation
    causal_link_type: DIRECT
    description: >-
      The imaging and operative finding that the dysplasia node names.
  - target: Persistent Functional Impairment of the Upper Limb
    causal_link_type: DIRECT
    description: >-
      Once the joint surfaces are deformed, function is limited by joint geometry rather
      than by nerve or muscle, which is why secondary orthopaedic procedures rather than
      nerve surgery are what address it.
  evidence:
  - reference: PMID:37503533
    reference_title: "Permanent Brachial Plexus Birth Injury: Helsinki Shoulder Protocol."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Shoulder dysplasia was diagnosed in 49% of 270 patients with permanent brachial plexus birth injury in our catchment area from 1995 to 2021."
    explanation: >-
      Gives the human frequency with its denominator and catchment, which is what makes
      it a population figure rather than a case-series impression.
  - reference: PMID:37503533
    reference_title: "Permanent Brachial Plexus Birth Injury: Helsinki Shoulder Protocol."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The age at detection of shoulder dysplasia dropped from mean 5.4 years in children born before 2000 to mean 3.9 months in children born after 2009."
    explanation: >-
      Shows that the age at which dysplasia is found is a property of surveillance
      practice rather than of the disease, which matters when reading older series.
- name: Persistent Functional Impairment of the Upper Limb
  biological_scale: ORGANISM
  description: >-
    The clinical endpoint in the minority who do not recover: a weak, internally rotated
    limb with limited abduction and external rotation, sometimes with elbow-flexion and
    forearm-supination deformity, and with usable motion further limited by
    cocontraction.
  downstream:
  - target: Elbow flexion contracture
    causal_link_type: DIRECT
    description: >-
      A recognised sequela of the persisting impairment, established late enough that it
      is treated as a fixed deformity rather than as part of the initial palsy.
  evidence:
  - reference: PMID:40958300
    reference_title: "Long-term outcomes and effectiveness of interventions in neonatal brachial plexus palsy: A systematic review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Functional recovery varied by surgical approach, with nerve grafts and transfers showing significant improvements in upper limb mobility and strength."
    explanation: >-
      Establishes that the residual impairment is a mobility-and-strength deficit that
      intervention can move, which is what makes it the endpoint of this chain.
phenotypes:
- category: Neurologic
  name: Upper limb muscle weakness
  description: >-
    Flaccid weakness of the shoulder and elbow on the affected side, present from birth.
    The classic posture is adduction, internal rotation and pronation with the wrist
    flexed.
  phenotype_term:
    preferred_term: Upper limb muscle weakness
    term:
      id: HP:0003484
      label: Upper limb muscle weakness
  frequency: VERY_FREQUENT
  evidence:
  - reference: PMID:30020632
    reference_title: "Erb Palsy."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Erb palsy most commonly results from an upper brachial plexus birth injury involving the C5–C6 nerve roots, with occasional extension to C7, leading to flaccid weakness or paralysis of the affected upper extremity."
    explanation: The defining clinical finding, stated with its anatomical basis.
- category: Musculoskeletal
  name: Limited passive shoulder external rotation
  description: >-
    The measured clinical sign of the contracture: fixed loss of passive external
    rotation, developing over the first months to years in the non-recovering group. It
    is named separately from the Shoulder Internal Rotation Contracture pathophysiology
    node, which is the mechanism, because the flat pathograph namespace would otherwise
    merge the two into one node.
  phenotype_term:
    preferred_term: Limitation of passive shoulder external rotation
    term:
      id: HP:0034392
      label: Joint contracture
  frequency: FREQUENT
  evidence:
  - reference: PMID:24388715
    reference_title: "The role of muscle imbalance in the pathogenesis of shoulder contracture after neonatal brachial plexus palsy: a study in a rat model."
    supports: SUPPORT
    directness: INDIRECT
    evidence_source: MODEL_ORGANISM
    snippet: "BACKGROUND: An internal rotation contracture of the shoulder is common after neonatal brachial plexus injuries due to subscapularis shortening and atrophy."
    explanation: >-
      States that the contracture is a common consequence in humans; the sentence is the
      background framing of a rat study, so it is graded MODEL_ORGANISM in keeping with
      the publication it comes from rather than with the claim it makes.
- category: Musculoskeletal
  name: Glenoid deformity with posterior humeral head subluxation
  description: >-
    The structural finding, in approximately half of permanent cases. Bound to the
    scapular morphology term because HPO has no glenohumeral dysplasia concept; the
    specific finding is kept in preferred_term. Named separately from the Glenohumeral
    Dysplasia pathophysiology node for the same namespace reason as the contracture
    above.
  phenotype_term:
    preferred_term: Glenohumeral dysplasia
    term:
      id: HP:0000782
      label: Abnormal scapula morphology
  frequency: FREQUENT
  evidence:
  - reference: PMID:37503533
    reference_title: "Permanent Brachial Plexus Birth Injury: Helsinki Shoulder Protocol."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Shoulder dysplasia was diagnosed in 49% of 270 patients with permanent brachial plexus birth injury in our catchment area from 1995 to 2021."
    explanation: >-
      Gives the frequency among permanent cases, which is the denominator this
      FREQUENT band refers to.
- category: Musculoskeletal
  name: Shoulder girdle muscle atrophy
  description: >-
    Wasting of the denervated shoulder girdle muscles, most consequentially the
    subscapularis, whose loss of bulk and length drives the contracture.
  phenotype_term:
    preferred_term: Shoulder girdle muscle atrophy
    term:
      id: HP:0003724
      label: Shoulder girdle muscle atrophy
  frequency: FREQUENT
  evidence:
  - reference: PMID:24388715
    reference_title: "The role of muscle imbalance in the pathogenesis of shoulder contracture after neonatal brachial plexus palsy: a study in a rat model."
    supports: SUPPORT
    directness: INDIRECT
    evidence_source: MODEL_ORGANISM
    snippet: "BACKGROUND: An internal rotation contracture of the shoulder is common after neonatal brachial plexus injuries due to subscapularis shortening and atrophy."
    explanation: Names the atrophy component alongside the shortening.
- category: Musculoskeletal
  name: Elbow flexion contracture
  description: >-
    A recognised late sequela, presenting as a fixed flexion deformity that persists
    despite physiotherapy and splinting and is then treated by serial casting or hinged
    bracing. In the largest reported series the mean deformity at treatment was 45.8
    degrees at a mean age of 12.2 years, so this is a deformity of later childhood
    rather than part of the neonatal presentation.
  phenotype_term:
    preferred_term: Fixed flexion deformity of the elbow
    term:
      id: HP:0002987
      label: Elbow flexion contracture
  evidence:
  - reference: PMID:42438048
    reference_title: "Serial Casting and Hinged Elbow Bracing in the Treatment of Fixed Flexion Deformity of the Elbow Following Obstetric Brachial Plexus Palsy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "BACKGROUND: Fixed flexion deformity (FFD) of the elbow is a recognized sequela of obstetric brachial plexus palsy (OBPP)."
    explanation: >-
      States the phenotype and its relation to the disease directly. No frequency is
      given: this is a treated case series of 73 patients, which is a numerator without
      a denominator of all obstetric brachial plexus palsy, so the frequency slot is
      left empty rather than estimated from it.
  - reference: PMID:42438048
    reference_title: "Serial Casting and Hinged Elbow Bracing in the Treatment of Fixed Flexion Deformity of the Elbow Following Obstetric Brachial Plexus Palsy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Mean pretreatment active FFD was 45.8±19.9 degrees and improved to 20.7±15.1 degrees after treatment, giving a mean improvement of 25.2 degrees (95% CI: 21.6-28.8 degrees; P<0.001; Cohen dz=1.49)."
    explanation: >-
      Quantifies the severity of the established deformity, which is what makes it a
      treated entity rather than a note in a follow-up list.
environmental:
- name: Shoulder dystocia at delivery
  description: >-
    Impaction of the anterior shoulder behind the pubic symphysis, requiring resolution
    manoeuvres. It is by a wide margin the strongest risk factor, and it is also the
    circumstance in which the traction that injures the plexus is applied.
  influences_mechanisms:
  - target: Excessive Lateral Traction on the Upper Brachial Plexus at Delivery
    environmental_effect: TRIGGERS
    causal_link_type: DIRECT
    description: >-
      Shoulder dystocia is the delivery geometry in which the head-to-shoulder angle is
      forced open, which is the mechanical event that stretches the plexus.
    evidence:
    - reference: PMID:39187951
      reference_title: "Epidemiology of Brachial Plexus Birth Injury and the Impact of Cesarean Section on Its Incidence."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Shoulder dystocia was the strongest risk factor for BPBI in the logistic regression model [adjusted odds ratio (AOR): 56.9, P <0.001]."
      explanation: >-
        Gives the adjusted effect size for the association between the exposure and the
        injury.
  evidence:
  - reference: PMID:41367186
    reference_title: "Risk factors for shoulder dystocia-related brachial plexus injuries: A case-control study."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "INTRODUCTION: Brachial plexus injury (BPI) is one of the major complications associated with shoulder dystocia."
    explanation: >-
      Establishes the exposure-outcome pairing that this environmental entry records.
  notes: >-
    No exposure_term is bound. ECTO is an ontology of chemical, dietary, social and
    physical environmental exposures; it has no concept for an intrapartum mechanical
    event of this kind, and binding a generic physical-force term would assert something
    less specific than the free text already says. HP:0011413 Shoulder dystocia exists as
    a phenotype term but describes the mother's delivery rather than an exposure of the
    infant, so it is not used here either.
- name: Cesarean delivery
  description: >-
    Protective rather than causative, and the only intervention with a measured effect on
    incidence. Delivery by cesarean section removes the geometry in which the traction is
    applied. The protection is largest where the risk is largest: in macrosomic newborns
    the adjusted odds ratio was 0.581, below the 1.000 reference for a normal-weight
    newborn delivered vaginally.
  influences_mechanisms:
  - target: Excessive Lateral Traction on the Upper Brachial Plexus at Delivery
    environmental_effect: PROTECTS_AGAINST
    causal_link_type: DIRECT
    description: >-
      Acts on the initiating mechanical event by avoiding the vaginal delivery in which
      the head-to-shoulder angle is forced open.
    evidence:
    - reference: PMID:39187951
      reference_title: "Epidemiology of Brachial Plexus Birth Injury and the Impact of Cesarean Section on Its Incidence."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Stratified analysis indicated C-section delivery was protective against BPBI across newborn weight classes, but the magnitude of this protective value was highest among newborns with macrosomia."
      explanation: >-
        Reports the protective effect and, importantly, that it is not uniform: it is
        strongest in the group at highest risk, which is what a mechanical account
        predicts.
  evidence:
  - reference: PMID:39187951
    reference_title: "Epidemiology of Brachial Plexus Birth Injury and the Impact of Cesarean Section on Its Incidence."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The AOR for a newborn with macrosomia born through C-section (AOR: 0.581, 95% CI: 0.365-0.925) was lower than that for a normal weight newborn born vaginally (AOR: 1.000, P =0.022)."
    explanation: >-
      Gives the adjusted effect size with its confidence interval and the comparator it
      is measured against.
  notes: >-
    No exposure_term is bound, for the same reason as the shoulder dystocia entry: ECTO
    has no concept for a mode of delivery. NCIT:C46088 (Cesarean Section) exists but is a
    procedure term rather than an exposure, and this record describes the infant's
    exposure rather than the mother's operation.
- name: Fetal macrosomia
  description: >-
    The upstream risk factor that makes the impaction likely, and the one that maternal
    diabetes and obesity act through. It is recorded here as a predisposing exposure
    rather than a trigger: macrosomia does not itself apply traction, it raises the
    probability that the shoulder impacts.
  influences_mechanisms:
  - target: Excessive Lateral Traction on the Upper Brachial Plexus at Delivery
    environmental_effect: PREDISPOSES
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    description: >-
      Acts through shoulder dystocia rather than directly. The known intermediate is the
      impaction itself, which is modeled as its own environmental entry above.
    evidence:
    - reference: PMID:27318182
      reference_title: "Shoulder dystocia: guidelines for clinical practice from the French College of Gynecologists and Obstetricians (CNGOF)."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Its main risk factors are previous SD and macrosomia, but both are poorly predictive; 50-70% of SD cases occur in their absence, and most deliveries when they are present do not result in SD."
      explanation: >-
        Names macrosomia as a main risk factor and, in the same sentence, states how
        poorly it predicts, which is why this link is PREDISPOSES rather than TRIGGERS.
  evidence:
  - reference: PMID:39187951
    reference_title: "Epidemiology of Brachial Plexus Birth Injury and the Impact of Cesarean Section on Its Incidence."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "An interaction between cesarean (C-) section and newborn weight was explored by defining BPBI rates in a stratified manner."
    explanation: >-
      Establishes newborn weight as an effect modifier of the injury rate, which is the
      basis for curating macrosomia as a separate exposure.
  notes: >-
    No exposure_term is bound. ECTO covers environmental exposures of the organism, not
    fetal growth status, and HP:0001520 (Large for gestational age) describes the infant
    rather than an exposure acting on it.
animal_models:
- name: Neonatal rat C5-C6 neurotomy model
  species: Rat
  genotype: Wild type, surgical C5-C6 neurotomy at postnatal day 5
  publication: PMID:18343282
  description: >-
    The workhorse model for the post-injury deformity. Sectioning C5-C6 in the newborn
    rat reproduces the internal rotation contracture in every animal within four weeks
    and goes on to reproduce the glenoid deformity, which is what makes it a model of
    the sequelae rather than only of the nerve lesion.
  modeled_mechanisms:
  - target: Shoulder Internal Rotation Contracture
    relationship: RECAPITULATES
    fidelity: HIGH
    model_scale: TISSUE
    description: >-
      Every animal developed the contracture on a defined timescale after the lesion.
    limitations: >-
      The lesion is a clean surgical neurotomy of known grade, whereas the human injury
      is a traction lesion of unknown and variable grade. The model therefore reproduces
      what happens after a severe lesion, and says nothing about the graded severity
      that determines which human infants reach this branch at all.
    readouts:
    - name: Shoulder internal rotation contracture at 4 weeks
      target: Shoulder Internal Rotation Contracture
      direction: INCREASED
      interpretation: Presence of the contracture in every operated animal within 4 weeks.
      evidence:
      - reference: PMID:18343282
        reference_title: "Brachial plexus birth palsy-associated shoulder deformity: a rat model study."
        supports: SUPPORT
        directness: INDIRECT
        evidence_source: MODEL_ORGANISM
        snippet: "RESULTS: All animals developed shoulder internal rotation contracture within 4 weeks after the C5, C6 neurotomy."
        explanation: The measurement behind this readout, with its timescale and completeness.
    evidence:
    - reference: PMID:18343282
      reference_title: "Brachial plexus birth palsy-associated shoulder deformity: a rat model study."
      supports: SUPPORT
      directness: INDIRECT
      evidence_source: MODEL_ORGANISM
      snippet: "CONCLUSIONS: This neonatal rat model clearly demonstrated typical shoulder deformities similar to that resulting from Erb's palsy."
      explanation: >-
        The authors' own claim that the model reproduces the human deformities, which is
        what licenses treating it as informative for this node.
  - target: Glenohumeral Dysplasia
    relationship: RECAPITULATES
    fidelity: MODERATE
    model_scale: TISSUE
    description: >-
      Glenoid version shifted from retroversion to anteversion with pseudoglenoid
      formation, subluxation and humeral head deformity.
    limitations: >-
      The direction of the version change is not the same as in humans, where the
      characteristic finding is increased glenoid retroversion with posterior
      subluxation. The model reproduces that a growing glenoid remodels under abnormal
      load, not the specific human deformity, and this entry does not use it to support
      the human dysplasia phenotype.
    readouts:
    - name: Glenoid version
      target: Glenohumeral Dysplasia
      direction: ALTERED
      interpretation: >-
        Measured shift in glenoid version, the bony correlate of the dysplasia node.
      evidence:
      - reference: PMID:18343282
        reference_title: "Brachial plexus birth palsy-associated shoulder deformity: a rat model study."
        supports: SUPPORT
        directness: INDIRECT
        evidence_source: MODEL_ORGANISM
        snippet: "Glenoid version changed from 2 degrees +/- 2 of retroversion (left side) to 8 degrees +/- 3 of anteversion."
        explanation: The quantitative readout, with its direction and dispersion.
    evidence:
    - reference: PMID:18343282
      reference_title: "Brachial plexus birth palsy-associated shoulder deformity: a rat model study."
      supports: SUPPORT
      directness: INDIRECT
      evidence_source: MODEL_ORGANISM
      snippet: "Both shoulders were harvested, decalcified, and transected in the axial plane for glenoid version measurement and shoulder histology."
      explanation: >-
        Records how the deformity was measured, which is what makes the version figure
        interpretable.
- name: Selective subscapularis denervation rat model
  species: Rat
  genotype: Wild type, selective subscapularis denervation
  publication: PMID:25124991
  description: >-
    The dissection experiment for the atrophy route. Denervating the subscapularis alone
    produced the contracture, establishing that route as sufficient.
  modeled_mechanisms:
  - target: Subscapularis Denervation Atrophy and Impaired Longitudinal Growth
    relationship: RECAPITULATES
    fidelity: MODERATE
    model_scale: TISSUE
    description: >-
      Isolates one muscle's denervation as a sufficient cause of the contracture.
    limitations: >-
      Selective single-muscle denervation does not occur in the human injury, where the
      upper trunk supplies several muscles at once. The experiment establishes
      sufficiency in principle; it cannot say how much of a given child's contracture
      this route contributes, and the authors say so.
    evidence:
    - reference: PMID:25124991
      reference_title: "The role of subscapularis muscle denervation in the pathogenesis of shoulder internal rotation contracture after neonatal brachial plexus palsy: a study in a rat model."
      supports: SUPPORT
      directness: INDIRECT
      evidence_source: MODEL_ORGANISM
      snippet: "Our study shows that subscapularis denervation, per se, could explain shoulder contracture after neonatal brachial plexus injury, though its relevance compared to other pathogenic factors needs further investigation."
      explanation: >-
        The sufficiency result together with the authors' explicit limitation, which is
        the basis for MODERATE rather than HIGH fidelity here.
- name: Selective suprascapular neurectomy rat model
  species: Rat
  genotype: Wild type, selective suprascapular neurectomy with subscapularis spared
  publication: PMID:24388715
  description: >-
    The complementary dissection experiment. Denervating only the external rotators,
    with the subscapularis intact and histologically unchanged, still produced the
    contracture.
  modeled_mechanisms:
  - target: Rotator Muscle Imbalance
    relationship: RECAPITULATES
    fidelity: MODERATE
    model_scale: TISSUE
    description: >-
      Establishes imbalance as a second sufficient route, independent of subscapularis
      atrophy.
    limitations: >-
      As with the subscapularis experiment, the lesion is selective in a way the human
      injury is not. What the pair of experiments establishes is that two routes are each
      sufficient, not their relative contribution in any patient.
    readouts:
    - name: Subscapularis fibre size and fibrosis
      target: Rotator Muscle Imbalance
      direction: UNCHANGED
      interpretation: >-
        A negative result, and the load-bearing one: the spared subscapularis was
        histologically normal, so the contracture in this arm cannot be attributed to it.
      evidence:
      - reference: PMID:24388715
        reference_title: "The role of muscle imbalance in the pathogenesis of shoulder contracture after neonatal brachial plexus palsy: a study in a rat model."
        supports: SUPPORT
        directness: INDIRECT
        evidence_source: MODEL_ORGANISM
        snippet: "No differences were found in subscapularis muscle fiber size and area of fibrosis between shoulders after suprascapular nerve injury."
        explanation: The measurement showing the spared muscle was unaffected.
    evidence:
    - reference: PMID:24388715
      reference_title: "The role of muscle imbalance in the pathogenesis of shoulder contracture after neonatal brachial plexus palsy: a study in a rat model."
      supports: SUPPORT
      directness: INDIRECT
      evidence_source: MODEL_ORGANISM
      snippet: "CONCLUSIONS: Our study supports the theory that shoulder muscle imbalance is a cause of shoulder contracture in patients with neonatal brachial plexus palsy."
      explanation: The conclusion this model link records.
treatments:
- name: Physical and Occupational Therapy
  description: >-
    First-line and universal: maintaining passive range of motion while waiting to see
    whether the nerve recovers. It is directed at preventing the contracture rather than
    at the nerve lesion.
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: physical therapy
    term:
      id: NCIT:C15302
      label: Physical Therapy
  target_mechanisms:
  - target: Shoulder Internal Rotation Contracture
    description: >-
      Aimed at the contracture, by maintaining length in the internal rotators through
      the period when the muscle is denervated and not growing.
- name: Botulinum Toxin Injection of the Internal Rotators
  description: >-
    Chemical weakening of the internal rotators to rebalance the joint. The measured
    benefit outlasts the toxin's pharmacological half-life, which is the observation that
    makes it more than a temporising measure: gains of 46 degrees of passive external
    rotation at four months, with 18 degrees still present at eleven months.
  therapeutic_modality: OTHER
  treatment_term:
    preferred_term: botulinum toxin chemodenervation
    term:
      id: NCIT:C157775
      label: Botulinum Toxin Therapy
    therapeutic_agent:
    - preferred_term: botulinum toxin type A
      term:
        id: CHEBI:3160
        label: Botulinum toxin type A
  target_mechanisms:
  - target: Rotator Muscle Imbalance
    description: >-
      Acts directly on the imbalance route by weakening the relatively preserved internal
      rotators, rather than by strengthening the denervated external rotators.
    evidence:
    - reference: PMID:32753228
      reference_title: "Outcomes of Botulinum Toxin Injection for Shoulder Internal Rotation Contractures in Infants with Brachial Plexus Birth Injury."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Subjects demonstrated a significant increase in passive external rotation of 46° (range, 10° to 90) at 4 months; an average improvement of 18° (range, -30° to 80°) persisted at 11 months after injection."
      explanation: >-
        Gives the effect size and its persistence beyond the toxin's half-life, which is
        what supports an effect on the underlying imbalance rather than a purely
        pharmacological one. Note the range crosses zero at eleven months, so some
        children lost ground.
  evidence:
  - reference: PMID:32753228
    reference_title: "Outcomes of Botulinum Toxin Injection for Shoulder Internal Rotation Contractures in Infants with Brachial Plexus Birth Injury."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Shoulder passive external rotation in adduction and Active Movement Scale external rotation scores were recorded before and after BTX-A injection."
    explanation: >-
      Records what was measured. This is a retrospective before-and-after series, not a
      controlled trial, which is the main limit on how the effect size should be read.
- name: Primary Nerve Reconstruction and Nerve Transfer
  description: >-
    Neuroma excision with grafting, or distal nerve transfers, when biceps recovery has
    not occurred by around three to six months. Nerve transfers reported grade 4 or
    better elbow flexion in all evaluable patients in one series. A systematic review of
    the whole literature is more measured: grafts and transfers both improve function,
    and no approach is established as superior.
  therapeutic_modality: SURGERY
  treatment_term:
    preferred_term: nerve reconstruction and nerve transfer
    term:
      id: NCIT:C15329
      label: Surgical Procedure
  target_mechanisms:
  - target: Denervation of C5-C6 Innervated Shoulder and Elbow Muscles
    description: >-
      The only treatment aimed at the nerve lesion itself, restoring axonal continuity to
      the denervated muscles before the downstream deformity is established.
    evidence:
    - reference: PMID:27543083
      reference_title: "Distal transfers as a primary treatment in obstetric brachial plexus palsy: a series of 20 cases."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Of the remainder, 11 had grade 4+ power of elbow flexion and six patients had grade 4 power at 1\u2009year follow-up; all had 4+ power of elbow flexion at final follow-up."
      explanation: >-
        Reports the reinnervation outcome for the target muscle. A small uncontrolled
        series in a selected injury grade, so it establishes that the approach can work
        rather than how it compares.
  evidence:
  - reference: PMID:40958300
    reference_title: "Long-term outcomes and effectiveness of interventions in neonatal brachial plexus palsy: A systematic review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "While nerve grafts and nerve transfers show promising results, there is no definitive consensus on their superiority, particularly regarding external shoulder rotation and hand function recovery."
    explanation: >-
      The systematic review's own hedge, which is the honest summary of the comparative
      evidence and is deliberately quoted rather than the single-series result above.
- name: Secondary Shoulder Reconstruction
  description: >-
    Procedures for established deformity: anterior shoulder and subscapularis release,
    tendon transfer, and humeral derotation osteotomy. Anterior release improved glenoid
    version from -32 to -12 degrees, and open subscapularis lengthening with joint
    relocation gave durable remodelling at ten years, so the deformed joint retains
    remodelling capacity if the abnormal force is removed.
  therapeutic_modality: SURGERY
  treatment_term:
    preferred_term: orthopedic surgical procedure
    term:
      id: NCIT:C16186
      label: Orthopedic Surgical Procedure
  target_mechanisms:
  - target: Glenohumeral Dysplasia
    description: >-
      Removes the deforming force and relocates the joint, after which the growing
      glenoid remodels. This is the therapeutic counterpart of the claim that the
      dysplasia is generated by sustained abnormal load rather than being a fixed primary
      malformation.
    evidence:
    - reference: PMID:30981548
      reference_title: "Isolated open anterior shoulder release in brachial plexus birth palsy."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "RESULTS: After a mean follow-up period of 23 months, glenoid version and the percentage of the humeral head anterior to the middle of the glenoid fossa significantly improved from -32° and 18%, respectively, to mean postoperative values of -12° (P < .001) and 45% (P < .001), respectively."
      explanation: >-
        Measures the bony remodelling after release on two axes, version and humeral head
        position, which is what supports the claim that the deformity is load-driven and
        partly reversible.
    - reference: PMID:31085034
      reference_title: "Development of the glenohumeral joint after subscapular release and open relocation in children with brachial plexus birth palsy: long-term results in 61 patients."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "The glenoid retroversion changed by 14.8° (95% confidence interval, 11.1°-18.4°; P < .01), from 25.4° to 10.6°, approaching a normal value."
      explanation: >-
        The same remodelling measured at a mean of 10.2 years, so the correction is
        durable rather than an early postoperative appearance. Note this is a
        before-and-after study without a control arm.
diagnosis:
- name: Clinical examination at birth with serial motor assessment
  description: >-
    Diagnosis is clinical: a flaccid arm at birth in the characteristic posture. What
    matters afterwards is serial assessment, because the decision that changes outcome is
    whether biceps function returns in the first months, and that is a longitudinal
    observation rather than a single test.
  presence: PRESENT
  evidence:
  - reference: PMID:25509702
    reference_title: "Brachial plexus birth palsy: the natural history, outcome of microsurgical repair and operative reconstruction."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "OBJECTIVE: To document the natural history of brachial plexus birth palsy in relation to the recovery of elbow flexion and shoulder flexion in the first six months of life; to assess the outcome after microsurgery of the brachial plexus in patients who had no recovery of bicep function at six months."
    explanation: >-
      Frames the diagnostic task as serial assessment of recovery against the six-month
      biceps milestone.
- name: Imaging and electrophysiology for lesion grade
  description: >-
    Reserved for infants who are not recovering. The question these answer is not whether
    there is an injury but what grade it is, and specifically whether roots have been
    avulsed, which cannot be repaired by grafting.
  presence: PRESENT
  evidence:
  - reference: PMID:12874720
    reference_title: "[Management of obstetrical brachial plexus palsy--own experience with the primary operative technique]."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "If spontaneous recovery does not occur within the first six months of life, investigations like electrophysiology, and CT-myelography and surgical exploration of the brachial plexus are recommended."
    explanation: >-
      States both the trigger for investigation and the modalities, and makes clear they
      follow rather than establish the diagnosis.
  - reference: PMID:39432686
    reference_title: "Diagnostic accuracy of MRI for detecting nerve injury in brachial plexus birth injury."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The mean sensitivity and mean specificity of MRI for detecting root avulsion was 68% (95% CI: 55%, 79%) and 89% (95% CI: 78%, 95%), respectively."
    explanation: >-
      Puts numbers on how much the imaging answers. A sensitivity of 68 per cent means a
      negative MRI does not exclude avulsion, which is why imaging informs the operative
      decision rather than making it.
differential_diagnoses:
- name: Clavicle fracture
  description: >-
    The other common birth injury of the same delivery, and the main early mimic: a
    newborn with a fractured clavicle also does not move the arm, from pain rather than
    from denervation. They share risk factors and can co-occur.
  evidence:
  - reference: PMID:42486682
    reference_title: "Risk and protective factors for birth-related clavicle fracture and brachial plexus birth injury: a national cohort study."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "OBJECTIVE: Clavicle fracture is the most common birth-related fracture, resulting in concerns and dissatisfaction, while brachial plexus birth injury (BPBI) is a severe complication with potential lifelong sequelae."
    explanation: >-
      Establishes the two as the paired birth injuries of the same event, which is what
      makes clavicle fracture the differential rather than an unrelated condition.
discussions:
- discussion_id: erb_two_sufficient_contracture_routes
  kind: KNOWLEDGE_GAP
  attaches_to:
  - pathophysiology#Subscapularis Denervation Atrophy and Impaired Longitudinal Growth
  - pathophysiology#Rotator Muscle Imbalance
  prompt: >-
    Denervation atrophy and rotator imbalance are each sufficient to produce the
    contracture in the rat. What is their relative contribution in a given child?
  rationale: >-
    Two selective-denervation experiments each produce the contracture on their own, and
    neither was designed to weigh them against the other. That is not an academic
    question, because the treatments act on different routes: botulinum toxin weakens the
    intact internal rotators and so targets imbalance, while therapy aimed at maintaining
    subscapularis length targets the atrophy route. Which one dominates in a particular
    child would predict which treatment helps them, and nothing measures it. One of the
    two papers raises the point itself.
  evidence:
  - reference: PMID:25124991
    reference_title: "The role of subscapularis muscle denervation in the pathogenesis of shoulder internal rotation contracture after neonatal brachial plexus palsy: a study in a rat model."
    supports: SUPPORT
    directness: INDIRECT
    evidence_source: MODEL_ORGANISM
    snippet: "Our study shows that subscapularis denervation, per se, could explain shoulder contracture after neonatal brachial plexus injury, though its relevance compared to other pathogenic factors needs further investigation."
    explanation: >-
      The authors state the open question directly: sufficiency is established, relative
      weight is not.
- discussion_id: erb_prevention_ceiling
  kind: KNOWLEDGE_GAP
  attaches_to:
  - environmental#Shoulder dystocia at delivery
  prompt: >-
    How much of the residual injury burden is preventable at all, given that most shoulder
    dystocia occurs without identifiable risk factors?
  rationale: >-
    Prevention here is obstetric, and it works: twelve years of multi-professional
    shoulder-dystocia simulation training was followed by a fall in brachial plexus injury
    from 7.4% to 1.3% of shoulder dystocia deliveries. But that is training in how to
    manage the event, not in how to avoid it. Risk-factor-based prevention has a hard
    ceiling, because half to two-thirds of shoulder dystocia happens in women with none of
    the recognised risk factors. Distinguishing the two kinds of prevention matters for
    what a service should invest in, and the literature does not separate their
    contributions.
  evidence:
  - reference: PMID:27318182
    reference_title: "Shoulder dystocia: guidelines for clinical practice from the French College of Gynecologists and Obstetricians (CNGOF)."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Its main risk factors are previous SD and macrosomia, but both are poorly predictive; 50-70% of SD cases occur in their absence, and most deliveries when they are present do not result in SD."
    explanation: >-
      States the ceiling on risk-factor-based prediction in both directions, poor
      sensitivity and poor specificity.
  - reference: PMID:25688719
    reference_title: "Prevention of brachial plexus injury-12 years of shoulder dystocia training: an interrupted time-series study."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "MAIN OUTCOMES: Neonatal morbidity (brachial plexus injury, humeral fracture, clavicular fracture, 5-minute Apgar score <7) and documented management of shoulder dystocia (resolution manoeuvres performed, traction applied, head-to-body delivery interval)."
    explanation: >-
      Records what the training study measured. It is an interrupted time series rather
      than a trial, so the fall in injury is a before-and-after association in one unit.
- discussion_id: erb_rat_glenoid_direction_mismatch
  kind: HUMAN_MODEL_MISMATCH
  attaches_to:
  - pathophysiology#Glenohumeral Dysplasia
  - animal_models#Neonatal rat C5-C6 neurotomy model
  prompt: >-
    Does the rat glenoid deformity model the human one, given that the version change goes
    in the opposite direction?
  rationale: >-
    The rat model reproduces the contracture faithfully and is the main evidence that the
    dysplasia is load-driven rather than primary. But its glenoid moves from retroversion
    to anteversion, whereas the human deformity is characterised by increasing retroversion
    with posterior subluxation. Quadrupedal shoulder loading is not bipedal shoulder
    loading, so the discrepancy is explicable, but it means the model supports the general
    claim that a growing glenoid remodels under sustained abnormal force and does not
    support the specific human deformity. This entry uses it for the former only, and the
    human dysplasia phenotype is evidenced from human data.
  evidence:
  - reference: PMID:18343282
    reference_title: "Brachial plexus birth palsy-associated shoulder deformity: a rat model study."
    supports: SUPPORT
    directness: INDIRECT
    evidence_source: MODEL_ORGANISM
    snippet: "Glenoid version changed from 2 degrees +/- 2 of retroversion (left side) to 8 degrees +/- 3 of anteversion."
    explanation: >-
      The measurement whose direction differs from the human finding, which is the
      mismatch this discussion records.
references:
- reference: PMID:30020632
  title: "Erb Palsy."
- reference: PMID:18343282
  title: "Brachial plexus birth palsy-associated shoulder deformity: a rat model study."
- reference: PMID:37503533
  title: "Permanent Brachial Plexus Birth Injury: Helsinki Shoulder Protocol."
notes: >-
  Not Neuralgic_Amyotrophy, which is the idiopathic or immune-mediated brachial
  plexopathy and is curated separately. Not the lower-trunk Klumpke form either, which is
  a distinct entity and is deliberately excluded from this entry rather than folded in.

  Evidence-grading note. The contracture routes, the aberrant reinnervation and the
  glenoid remodelling rest on neonatal rat work. Every evidence item drawn from those
  publications carries evidence_source MODEL_ORGANISM with directness INDIRECT, including
  the ones whose quoted sentence is about humans: evidence_source classifies the
  publication, not the claim. The human endpoints, the dysplasia frequency, the incidence
  and the treatment outcomes are evidenced from clinical series. The distinction is
  deliberate, because this is a condition where the mechanism is animal work and the
  outcomes are clinical series, and collapsing the two would overstate what is known
  about the human pathogenesis.

  Research consumption, stated rather than left to be inferred. The openscientist report
  fetched 46 references into the cache; this entry cites 20. The uncited remainder is
  mostly surgical-technique and outcome series for procedures the entry already models at
  the level of the mechanism they act on (tendon transfer variants, arthroscopic release
  variants, neurotization techniques), which would add operative detail without adding
  mechanism. Two phenotypes the report proposed are deliberately not curated because no
  cached source states them: an absent or reduced Moro reflex on the affected side, and
  upper limb undergrowth. Both are real and well known clinically; neither is quotable
  from anything in this PR, so they are recorded here rather than asserted.

  The openscientist deep-research report committed alongside this entry offered
  HP:0031843 as "Shoulder contracture". That code is Abnormally slow thought process. It
  was caught by the report's own term-validation section and never bound. The report's
  reference validation was clean, 40 of 40 verified with 9 of 9 quotes valid, and its
  causal chain is the backbone of the pathophysiology section here, but every snippet in
  this entry was taken from the cached reference text directly rather than from the
  report.

  No datasets block. This is an acquired mechanical injury with no molecular profiling
  literature; searching the term returns unrelated work.

📚

References & Deep Research

References

3

PMID:30020632

Erb Palsy.

No top-level findings curated for this source.

PMID:18343282

Brachial plexus birth palsy-associated shoulder deformity: a rat model study.

No top-level findings curated for this source.

PMID:37503533

Permanent Brachial Plexus Birth Injury: Helsinki Shoulder Protocol.

No top-level findings curated for this source.

Deep Research

1

Deep research results are used as seeds for research; they do not undergo the same validation as the main records and may contain errors. How we use deep research.

Evaluations and curation notes (2)

Record notes

Not Neuralgic_Amyotrophy, which is the idiopathic or immune-mediated brachial plexopathy and is curated separately. Not the lower-trunk Klumpke form either, which is a distinct entity and is deliberately excluded from this entry rather than folded in. Evidence-grading note. The contracture routes, the aberrant reinnervation and the glenoid remodelling rest on neonatal rat work. Every evidence item drawn from those publications carries evidence_source MODEL_ORGANISM with directness INDIRECT, including the ones whose quoted sentence is about humans: evidence_source classifies the publication, not the claim. The human endpoints, the dysplasia frequency, the incidence and the treatment outcomes are evidenced from clinical series. The distinction is deliberate, because this is a condition where the mechanism is animal work and the outcomes are clinical series, and collapsing the two would overstate what is known about the human pathogenesis. Research consumption, stated rather than left to be inferred. The openscientist report fetched 46 references into the cache; this entry cites 20. The uncited remainder is mostly surgical-technique and outcome series for procedures the entry already models at the level of the mechanism they act on (tendon transfer variants, arthroscopic release variants, neurotization techniques), which would add operative detail without adding mechanism. Two phenotypes the report proposed are deliberately not curated because no cached source states them: an absent or reduced Moro reflex on the affected side, and upper limb undergrowth. Both are real and well known clinically; neither is quotable from anything in this PR, so they are recorded here rather than asserted. The openscientist deep-research report committed alongside this entry offered HP:0031843 as "Shoulder contracture". That code is Abnormally slow thought process. It was caught by the report's own term-validation section and never bound. The report's reference validation was clean, 40 of 40 verified with 9 of 9 quotes valid, and its causal chain is the backbone of the pathophysiology section here, but every snippet in this entry was taken from the cached reference text directly rather than from the report. No datasets block. This is an acquired mechanical injury with no molecular profiling literature; searching the term returns unrelated work.

Create: Erb Palsy (upper brachial plexus birth injury) · 2026-09-07T17:55:47Z · View source

De novo curation of MONDO:0700303 (Erb palsy), an acquired mechanical injury rather than a Mendelian disorder. Pathophysiology is a causal chain from intrapartum traction through graded stretch injury of the C5-C6 upper trunk and denervation, branching into spontaneous recovery (the dominant outcome) and, in the minority, two independently sufficient routes to internal rotation contracture (subscapularis denervation atrophy, and rotator imbalance) plus aberrant reinnervation through a neuroma-in-continuity, converging on contracture and then glenohumeral dysplasia. 50 evidence snippets, all exact-quote verified. Evidence grading is the point of interest here: the contracture mechanism rests on neonatal rat work and those edges carry evidence_source MODEL_ORGANISM with directness INDIRECT throughout, while the human endpoints and treatment outcomes are evidenced from clinical series. Three rat models curated with modeled_mechanisms, per-link fidelity and limitations, including a HUMAN_MODEL_MISMATCH for the glenoid version change, which goes in the opposite direction to the human deformity. Deep research: one openscientist run, committed, 40/40 citations verified and 9/9 quotes valid; its causal chain is the backbone of the pathophysiology section. Its term validation caught that the report offered HP:0031843 for shoulder contracture, which is Abnormally slow thought process; that term was never bound. A separate error the report and I shared, UBERON:0001812 for brachial plexus, was caught by just validate-terms: that code is palpebral conjunctiva, and the correct term is UBERON:0001814 brachial nerve plexus. 27 reference_title values were corrected against the cache after the reference validator flagged them. Validated with just validate, check-entity-refs, check-causal-targets, check-duplicate-keys, check-enum-values, check-qualifier-terms, check-environmental-evidence and the four snippet gates, all passing.

OpenScientist ▸

Erb Palsy — Comprehensive Disease Characterization Report

openscientist-autonomous 39 citations 2026-09-07T17:28:35.805162

Erb Palsy — Comprehensive Disease Characterization Report

Disease: Erb Palsy (Erb–Duchenne Palsy) MONDO ID: MONDO:0700303 · ICD-10: P14.0 · Category: Acquired (non-genetic birth injury)

Summary

Erb palsy is an acquired, non-genetic mechanical traction/stretch injury of the upper brachial plexus (nerve roots C5–C6, sometimes extending to C7) sustained during birth. It is the single most common subtype of obstetric brachial plexus injury (OBPI), accounting for roughly two-thirds of all cases (66.6% in a German national cohort). Reported incidence ranges from ~0.15–1.5 per 1000 live births using administrative data, rising to ~14.5 per 1000 under active prospective surveillance, reflecting that many mild neuropraxic injuries at birth go under-recorded. The strongest single risk factor is shoulder dystocia (adjusted odds ratio ~57), with fetal macrosomia, maternal diabetes, and maternal obesity as major contributors; cesarean delivery is protective, most strongly in macrosomic infants.

Clinically the newborn presents with a flaccid, adducted, internally rotated arm with an extended, pronated forearm — the classic "waiter's-tip" posture. Diagnosis is clinical (Narakas classification), supported by MRI (modest sensitivity ~68% for root avulsion) and electrophysiology. The natural history is favorable: 80–95% of infants recover spontaneously, with recovery of biceps (elbow flexion) function by ~3 months being the pivotal prognostic milestone. In the ~5–20% with persistent injury, denervation of the shoulder muscles (particularly the subscapularis) plus muscle imbalance drives a shoulder internal-rotation contracture and secondary glenohumeral dysplasia (seen in ~49% of permanent cases), the chief long-term morbidity.

Management follows a staged, time-sensitive ladder: physiotherapy/occupational therapy first-line to maintain range of motion; botulinum toxin A to counter early contracture; microsurgical nerve reconstruction (nerve grafting after neuroma excision) or distal nerve transfers when biceps recovery is absent by ~3–6 months; and secondary orthopedic procedures (soft-tissue releases, tendon transfers, humeral derotation osteotomy, radioulnar synostosis) for residual deformity. Prevention is fundamentally obstetric: multi-professional shoulder-dystocia simulation training and maternal glycemic control measurably reduce brachial plexus injury at birth, though 50–70% of shoulder dystocia occurs without identifiable risk factors, limiting predictive prevention. Because Erb palsy is a mechanical acquired injury, there is no causal gene, no OMIM Mendelian entry, no ClinVar variant, and no heritable transmission — sections of this template addressing genetics, epigenetics, and inheritance are largely not applicable, and this is documented explicitly below.

Key Findings

Finding 1 — Erb palsy is the most common OBPI subtype; incidence ~0.9–1.5 per 1000 live births

Erb palsy is the dominant clinical presentation among obstetric brachial plexus injuries. In a German national cohort (2005–2018; n = 2,069 infants hospitalized with OBPI in the first year of life), Erb palsy (ICD-10 P14.0) was the most frequent subtype at 66.60%, and overall OBPI incidence declined by 47.57%, from 0.28 per 1000 births in 2005 to 0.15 in 2018 (p < 0.001) — a trend attributed to improved obstetric practice and rising cesarean rates (PMID: 40315612). The US Kids' Inpatient Database found brachial plexus birth injury (BPBI) rates steady at ~0.9–1.1 per 1000 live births between 2006 and 2019 (PMID: 39187951). A 2021–2024 prospective surveillance study using real-time reporting found a substantially higher incidence of 14.5 per 1000 live births at birth, dropping to 3.6 per 1000 for injuries persisting beyond 2 months — demonstrating that administrative datasets undercount mild, transient neuropraxias (PMID: 41616322).

"Erb palsy was the most frequent OBPI subtype (66.60%)." — PMID: 40315612

Finding 2 — Shoulder dystocia is the strongest risk factor; cesarean delivery is protective

The mechanical origin of Erb palsy is reflected in its risk-factor profile. In a US Kids' Inpatient Database logistic-regression analysis, shoulder dystocia was the strongest predictor of BPBI (adjusted OR 56.9, p < 0.001), and cesarean delivery was protective across all newborn weight classes, with the greatest protection in macrosomic infants (macrosomic + C-section AOR 0.581, 95% CI 0.365–0.925) (PMID: 39187951). A prospective shoulder-dystocia cohort found that neonatal BPI at 48 hours was associated with maternal BMI > 30 kg/m² (OR 7.91, 95% CI 1.3–47.7), shoulder dystocia lasting > 120 s (OR 14.4, 95% CI 1.7–121.8), and operative delivery (OR 6.8, 95% CI 1.2–37.6) (PMID: 39411814). Earlier US data (KID 1997–2012) similarly identified shoulder dystocia, fetal macrosomia, and gestational diabetes as the highest-risk factors, with a protective effect of multiple birth mates (PMID: 31856038). Additionally, resolution of shoulder dystocia requiring ≥3 maneuvers doubled the neonatal composite adverse outcome risk and specifically raised brachial plexus palsy risk (aIRR 2.58, 95% CI 1.45–4.60) (PMID: 40239714).

"Shoulder dystocia was the strongest risk factor for BPBI in the logistic regression model [adjusted odds ratio (AOR): 56.9, P <0.001]." — PMID: 39187951

Risk / protective factor	Effect size	Source
Shoulder dystocia	AOR 56.9 (p<0.001)	PMID 39187951
Shoulder dystocia > 120 s	OR 14.4 (95% CI 1.7–121.8)	PMID 39411814
Maternal BMI > 30 kg/m²	OR 7.91 (95% CI 1.3–47.7)	PMID 39411814
Operative (assisted vaginal) delivery	OR 6.8 (95% CI 1.2–37.6)	PMID 39411814
≥3 maneuvers to resolve dystocia	aIRR 2.58 (95% CI 1.45–4.60)	PMID 40239714
Cesarean delivery (macrosomic)	AOR 0.581 (95% CI 0.365–0.925) — protective	PMID 39187951

Finding 3 — Most cases recover spontaneously; surgery is indicated when biceps recovery is absent by 3–6 months

The natural history of Erb palsy is favorable. Multiple series report 80–95% spontaneous recovery (PMID: 12874720). A natural-history cohort documented spontaneous recovery in 59 of 81 patients (73%), with a functional biceps typically achieved by 10 months (PMID: 25509702). A prospective OBPI cohort reported recovery in 24 of 28 infants (85.7%) and permanent injury in 4 of 28 (14.3%); notably, all permanent cases had shoulder dystocia (p = 0.007) (PMID: 40843939). The classic surgical criterion, associated with Tassin and Gilbert, holds that infants with no recovery of biceps function by 3 months should undergo microsurgical exploration/repair without delay (PMID: 8838992). This is nuanced by decision-analytic modeling favoring delayed repair at 12 months for quality-of-life optimization, since early surgery may be overly aggressive for infants who would recover spontaneously (PMID: 24483255).

"80 to 95% of these lesions recover spontaneously." — PMID: 12874720 "babies who have no recovery of the biceps function by three months of age should be operated without delay." — PMID: 8838992

Finding 4 — Diagnosis is clinical (Narakas classification); MRI has modest sensitivity for avulsion; glenohumeral dysplasia is a major sequela

Diagnosis rests on clinical examination and the Narakas classification (grade I: C5–C6; grade II: C5–C7; grade III: C5–T1; grade IV: C5–T1 with Horner syndrome). A meta-analysis of 8 studies (116 children) found MRI had a mean sensitivity of 68% (95% CI 55–79%) and specificity of 89% (95% CI 78–95%) for detecting root avulsion versus surgical exploration, with pseudomeningocele an unreliable marker (PMID: 39432686); a 3T single-center series reported concordant accuracy (68% overall, 67% sensitivity, 92% specificity) (PMID: 41451467). Clinical classification does not map perfectly onto anatomical injury: among Narakas 1 patients, only 23% had isolated C5–C6 injury, while 55% had additional C7/C8/T1 involvement on MRI, and C6 was the most commonly injured/avulsed root (PMID: 40828115). Shoulder dysplasia was diagnosed in 49% of 270 patients with permanent BPBI, underscoring glenohumeral dysplasia as the principal long-term structural sequela (PMID: 37503533).

"The mean sensitivity and mean specificity of MRI for detecting root avulsion was 68% (95% CI: 55%, 79%) and 89% (95% CI: 78%, 95%), respectively." — PMID: 39432686

Finding 5 — Shoulder internal-rotation contracture arises from denervation-induced impaired subscapularis growth and muscle imbalance (rat models)

The mechanism of the contracture that defines chronic Erb palsy has been dissected in neonatal rat models of brachial plexus injury (NBPI). After C5–C6 neurotomy/crush at postnatal day 5, all animals developed internal-rotation contracture within 4 weeks, with external-rotation loss progressing from 52° to 82° over 1–4 months, and glenoid version shifting from 2° retroversion to 8° anteversion with pseudoglenoid formation, subluxation, and glenoid/humeral head deformity — recapitulating human glenohumeral dysplasia (PMID: 18343282). Two complementary mechanisms were isolated: (a) denervation — selective subscapularis denervation alone caused 58° external-rotation loss and 69% muscle mass loss with reduced fiber size (PMID: 25124991); and (b) muscle imbalance — suprascapular neurectomy sparing the subscapularis also produced contracture (66° ER loss) by unbalancing internal vs. external rotators (PMID: 24388715). Cocontractions (simultaneous firing of antagonist muscles) are attributed to aberrant reinnervation through a neuroma-in-continuity, where regenerating axons reach the wrong target muscles (PMID: 38263956). Glenoid deformity severity correlates with measurable gait/limb-function impairment in these models (PMID: 29244216).

"subscapularis denervation, per se, could explain shoulder contracture after neonatal brachial plexus injury" — PMID: 25124991

Finding 6 — Prevention is primarily obstetric: shoulder-dystocia simulation training and glycemic control reduce injury

Because Erb palsy is mechanically caused at delivery, prevention targets obstetric practice. An interrupted time-series study over 12 years in Bristol found that after introducing multi-professional shoulder-dystocia simulation training, the use of at least one resolution maneuver rose from 46.3% to 99.8%, and brachial plexus injury at birth fell from 7.4% (24/324) pre-training to 1.3% (7/562) in late training (p < 0.01) (PMID: 25688719). French CNGOF guidelines establish that gestational-diabetes care reduces macrosomia and shoulder-dystocia risk (LE1, Grade A), that physical activity plus dietary measures in obese women reduce macrosomia (Grade A), and set estimated-fetal-weight thresholds for cesarean delivery (PMID: 27318182). Importantly, 50–70% of shoulder-dystocia cases occur without identifiable risk factors, capping the achievable benefit of risk-based prevention (PMID: 27318182).

"50-70% of SD cases occur in their absence, and most deliveries when they are present do not result in SD" — PMID: 27318182

Finding 7 — Treatment follows a staged ladder: physiotherapy → botulinum toxin → nerve reconstruction/transfers → secondary orthopedic procedures

Conservative therapy (physiotherapy/occupational therapy) is first-line to maintain passive range of motion and prevent contractures. Botulinum toxin A injected into the internal rotators improves passive external rotation (~46° gain at 4 months) and can defer or avoid tendon transfer in some children (PMID: 32753228). Primary microsurgery — nerve grafting after neuroma excision, plus neurotization — is indicated when biceps recovery is absent by ~3–6 months. Distal nerve transfers as primary treatment in Narakas I injuries (spinal accessory → suprascapular nerve, plus Oberlin ulnar-fascicle → biceps) achieved ≥grade 4 elbow flexion in all 17 evaluable patients (mean Mallet 15) (PMID: 27543083); a structured pediatric rehabilitation protocol (DAFRA) after SAN–SSN transfer achieved full external rotation against gravity in 71.4% (PMID: 41500917). Secondary orthopedic procedures address residual deformity: subscapularis/anterior shoulder release improved glenoid version from −32° to −12° (PMID: 30981548); open subscapularis lengthening with joint relocation gave durable glenohumeral remodeling at 10-year follow-up (PMID: 31085034); latissimus dorsi/teres major tendon transfers, humeral derotation osteotomy, and radioulnar synostosis for supination deformity round out the toolkit (PMID: 42568170). A systematic review of 965 patients confirmed that nerve grafts and transfers produce significant long-term gains in shoulder, elbow, and wrist function, though no single approach is universally superior (PMID: 40958300).

"Botulinum toxin A injections result in improvement in IRC due to BPBI, which is sustained beyond the expected half-life of 3 months." — PMID: 32753228

Finding 8 — Integrated synthesis: Erb palsy as an acquired, non-genetic C5–C6 birth traction injury

Synthesizing across all disease-characterization domains: Erb palsy is (1) the most common OBPI subtype (66.6%; PMID: 40315612), incidence ~0.9–1.5/1000 (PMID: 39187951); (2) caused by mechanical stretch/overstretching of C5–C6/upper trunk during delivery, with shoulder dystocia the strongest risk factor (AOR 56.9) and cesarean protective (PMID: 39187951); (3) without any genetic or infectious cause (no OMIM/ClinVar gene); (4) 80–95% spontaneously recovering, with biceps recovery by 3 months pivotal (PMID: 12874720, PMID: 8838992); (5) producing secondary internal-rotation contracture and glenohumeral dysplasia (49% of permanent cases) via denervation and muscle imbalance (PMID: 25124991, PMID: 24388715, PMID: 37503533); (6) treated by a staged ladder (PMID: 32753228, PMID: 27543083, PMID: 40958300); and (7) prevented obstetrically (PMID: 27318182, PMID: 25688719). ICD-10 P14.0; MONDO:0700303.

"overstretching of one or more cervical and thoracic nerve roots (C5-T1)" — PMID: 41588374

Full Report by Section

1. Disease Information

Overview. Erb palsy (Erb–Duchenne palsy) is a paralysis of the upper arm and shoulder caused by injury to the upper trunk of the brachial plexus (C5–C6, sometimes C7), most commonly sustained during birth through lateral traction on the neck/head as the shoulder is delivered. It is the most common form of obstetric brachial plexus injury.

Key identifiers. - MONDO: MONDO:0700303 - ICD-10: P14.0 (Erb paralysis due to birth injury) - ICD-11: structural birth injury of brachial plexus (injury of brachial plexus codes) - MeSH: "Brachial Plexus Neuropathies" / "Neonatal Brachial Plexus Palsy"; historically indexed under "Paralysis, Obstetric" - OMIM: Not applicable — Erb palsy is an acquired mechanical injury, not a Mendelian disorder; there is no OMIM entry with a causal gene. - Orphanet: Not a rare-disease genetic entry; obstetric brachial plexus palsy is captured as an acquired peripartum condition.

Synonyms / alternative names: Erb–Duchenne palsy; Erb's palsy; Duchenne–Erb paralysis; obstetric/obstetrical brachial plexus palsy or injury (OBPP/OBPI); brachial plexus birth injury (BPBI); neonatal brachial plexus palsy (NBPP); upper brachial plexus palsy; "waiter's-tip" deformity (describing posture, not a formal synonym).

Information source type. Evidence derives from aggregated disease-level resources (national inpatient/administrative databases, prospective surveillance cohorts, natural-history and surgical case series, and animal models), supplemented by individual-patient clinical follow-up cohorts. It is not a variant/EHR-genomic entity.

2. Etiology

Primary cause — mechanical. Erb palsy is caused by traction/stretch (and, in severe cases, rupture or avulsion) of the C5–C6 nerve roots and upper trunk during delivery, typically when the fetal head and neck are laterally displaced away from the shoulder. It is not genetic, infectious, toxic, or metabolic in origin.

Risk factors (all environmental/obstetric — no genetic risk loci apply): - Shoulder dystocia — strongest factor, AOR 56.9 (PMID: 39187951); prolonged (>120 s) dystocia OR 14.4 (PMID: 39411814); ≥3 resolution maneuvers aIRR 2.58 (PMID: 40239714). - Fetal macrosomia and large-for-gestational-age infants (PMID: 31856038). - Maternal diabetes / gestational diabetes (PMID: 31856038, PMID: 27318182). - Maternal obesity (BMI > 30, OR 7.91) (PMID: 39411814). - Operative (assisted) vaginal delivery (forceps/vacuum), OR 6.8 (PMID: 39411814). - Anatomical predisposition — a prefixed brachial plexus and the neonate's high head:body ratio and weak neck musculature increase susceptibility to traction (PMID: 33904192). - Socioeconomic deprivation has been associated with OBPP incidence (PMID: 37694876).

Protective factors. - Cesarean delivery — protective across weight classes, strongest in macrosomia (AOR 0.581) (PMID: 39187951). - Maternal glycemic control and weight management reduce macrosomia and thereby dystocia risk (PMID: 27318182). - No genetic protective variants apply.

Gene–environment interactions: Not applicable — there is no established genetic contribution to Erb palsy risk.

3. Phenotypes

The core phenotype is a flaccid, adducted, internally rotated arm with an extended, pronated forearm and flexed wrist — the "waiter's-tip" posture — present at birth (neonatal onset). Grip is typically preserved (C8–T1 spared) in classic upper-trunk Erb palsy, distinguishing it from total plexus palsy.

Phenotype	Type	HPO suggestion	Onset	Severity/progression	Frequency
Upper limb paralysis/weakness (shoulder abduction, external rotation, elbow flexion)	Clinical sign	HP:0003484 (Upper limb muscle weakness)	Neonatal/congenital	Variable; mostly improving	~100% at presentation
"Waiter's-tip" posture (arm adducted, internally rotated, forearm pronated)	Physical manifestation	HP:0011461 (neonatal-onset, approximate)	Neonatal	Variable	Characteristic
Absent/reduced Moro reflex on affected side	Clinical sign	HP:0001319 (approximate)	Neonatal	—	Common
Shoulder internal-rotation contracture	Physical manifestation	HP:0031843 (Shoulder contracture, approximate)	Develops over months in persistent cases	Progressive if untreated	Major in persistent cases
Glenohumeral dysplasia/joint deformity	Clinical sign (imaging)	HP:0006633 (Glenoid dysplasia, approximate)	Infancy–childhood	Progressive	~49% of permanent cases (PMID 37503533)
Limb-length/muscle atrophy of affected arm	Physical manifestation	HP:0009824 (Upper limb undergrowth)	Childhood	Slowly progressive	Persistent cases
Elbow flexion contracture / forearm supination deformity	Physical manifestation	HP:0001377 (Limited elbow extension)	Childhood	Progressive	Subset

Quality-of-life impact. Persistent Erb palsy impairs bimanual activities of daily living, dressing, and self-care; residual weakness, contracture, cosmetic asymmetry, and limb-length discrepancy affect function and psychosocial well-being. Formal QoL instrument data (EQ-5D/SF-36/PROMIS) specific to Erb palsy are sparse; functional outcomes are typically measured with the Mallet score and the Active Movement Scale (AMS) rather than generic QoL tools (PMID: 41500917, PMID: 40958300).

4. Genetic / Molecular Information

Not applicable. Erb palsy is an acquired mechanical birth injury. There is: - No causal gene (no OMIM Mendelian entry). - No pathogenic variants (no ClinVar/HGMD entries; no ACMG classification applies). - No allele frequencies, no somatic/germline distinction. - No modifier genes established. (The only "genetic-adjacent" susceptibility is anatomical variation such as a prefixed brachial plexus, which is not a molecular genetic trait; PMID: 33904192.) - No disease-specific epigenetic changes or chromosomal abnormalities.

This absence is itself an informative characterization: knowledge-base fields for causal genes, variants, inheritance, and epigenetics should be marked "not applicable — acquired non-genetic injury."

5. Environmental Information

The relevant "environmental" factors are peripartum mechanical and maternal-metabolic rather than toxic/infectious: - Mechanical: lateral neck traction during delivery, shoulder dystocia, instrumented delivery. - Maternal-metabolic: diabetes/gestational diabetes and obesity (via macrosomia). - Lifestyle: maternal physical activity and dietary control reduce risk indirectly by reducing macrosomia (PMID: 27318182). - Infectious agents: Not applicable — no pathogen causes or triggers Erb palsy. - Toxins/radiation/pollution/occupational exposure: Not applicable.

6. Mechanism / Pathophysiology

Ordered causal chain (initiating lesion → clinical manifestation):

During delivery (frequently complicated by shoulder dystocia/macrosomia), excessive lateral traction increasing the head-to-shoulder angle stretches the upper brachial plexus → results in overstretching of the C5–C6 (± C7) roots and upper trunk (PMID: 41588374, PMID: 39187951).
Stretch leads to a graded nerve injury — neuropraxia (conduction block), axonotmesis (axon disruption with intact sheath), neurotmesis (rupture), or, most severe, root avulsion from the spinal cord.
The nerve lesion results in partial or complete denervation of upper-limb muscles supplied by C5–C6: deltoid, supraspinatus, infraspinatus, biceps, brachialis, and subscapularis. (GO: muscle denervation; cell types: CL:0000100 motor neuron, CL:0008002 skeletal muscle fiber.)
Branch A — spontaneous recovery (80–95%): neuropraxic/mild axonotmetic fibers remyelinate/regenerate, restoring biceps and shoulder function, typically with biceps recovery by ~3 months (PMID: 12874720, PMID: 8838992).
Branch B — persistent injury (~5–20%): severe axonotmesis, rupture, or avulsion leads to incomplete/aberrant reinnervation.
5a. Denervation atrophy of the subscapularis and impaired muscle growth during a period of rapid skeletal growth results in a relatively short, stiff internal rotator → shoulder internal-rotation contracture (PMID: 25124991).
5b. Muscle imbalance between (relatively preserved) internal rotators and (weak, denervated) external rotators contributes to the same contracture even when the subscapularis is spared (PMID: 24388715).
5c. Aberrant reinnervation through a neuroma-in-continuity misroutes regenerating axons to antagonist muscles → cocontractions (e.g., simultaneous biceps/triceps firing), limiting usable motion (PMID: 38263956).
Sustained contracture and abnormal muscle forces across the growing glenohumeral joint result in posterior humeral-head subluxation, glenoid retroversion/pseudoglenoid formation, and glenohumeral dysplasia — demonstrated in rat NBPI models (glenoid version shifting from retroversion toward anteversion) and observed in ~49% of human permanent cases (PMID: 18343282, PMID: 37503533).
The combination manifests clinically as a weak, internally rotated, functionally impaired upper limb with limited abduction/external rotation, and secondary elbow-flexion and forearm-supination deformities in some (PMID: 42568170).

Upstream vs. downstream. Upstream: the mechanical nerve lesion and denervation. Downstream: muscle atrophy/growth impairment, muscle imbalance, aberrant reinnervation → contracture → bony glenohumeral dysplasia. Steps 5a–5c are demonstrated primarily in rat models (inference to humans is strong but model-based); the human structural endpoint (dysplasia) is well documented clinically.

Molecular/cellular processes involved: peripheral nerve axonal injury and Wallerian degeneration/regeneration; muscle denervation atrophy (reduced fiber cross-sectional area, ~69% mass loss in denervated subscapularis; PMID: 25124991); impaired skeletal-muscle longitudinal growth; endochondral/joint remodeling of the glenoid. GO term suggestions: GO:0031102 (neuron projection regeneration); GO:0043403 (skeletal muscle tissue regeneration); GO:0014732 (skeletal muscle atrophy). CL suggestions: CL:0000100 (motor neuron), CL:0008002 (skeletal muscle fiber), CL:0000138 (chondrocyte, for glenoid remodeling). No canonical intracellular signaling cascade (Wnt/MAPK/mTOR/PI3K–AKT) is disease-defining; this is a structural/mechanical injury rather than a signaling disorder.

7. Anatomical Structures Affected

Organ/system level (primary): peripheral nervous system — the brachial plexus, upper trunk (C5–C6 roots). UBERON: UBERON:0001812 (brachial plexus); UBERON:0000010 (peripheral nervous system).
Secondary/complication level: shoulder girdle musculature and the glenohumeral joint (UBERON:0001470), with secondary bony deformity of the glenoid/scapula (UBERON:0006849 glenoid; UBERON:0006849/UBERON:0000976 humeral head). The musculoskeletal system is secondarily involved.
Tissue level: nervous tissue (peripheral nerve) primarily; skeletal muscle tissue (subscapularis, deltoid, biceps, infraspinatus/supraspinatus) and cartilage/bone secondarily.
Cell level: motor neurons/axons (CL:0000100), Schwann cells (CL:0002573), skeletal muscle fibers (CL:0008002), chondrocytes (CL:0000138).
Subcellular level: axonal cytoskeleton and myelin sheath; no organelle-specific defect. GO cellular component: axon (GO:0030424), myelin sheath (GO:0043209).
Localization / lateralization: unilateral in the overwhelming majority; affects the shoulder that was impacted during delivery. Bilateral involvement is rare (associated with breech delivery).

8. Temporal Development

Onset: congenital/neonatal — present at or immediately after birth; onset is acute (a single mechanical event).
Course branches:
Recovery branch: rapid improvement over weeks to months; biceps recovery by ~3 months is the key favorable prognostic sign; most recover by 10–12 months (PMID: 25509702).
Persistent branch: if recovery is incomplete, deformities (contracture, dysplasia) progress slowly through childhood as the limb grows.
Disease "stages" (functional/persistent cases): early denervation → developing contracture → established glenohumeral dysplasia → fixed bony deformity.
Duration: self-limited in the majority; chronic/lifelong impairment in persistent cases.
Remission: predominantly spontaneous; treatment-induced improvement via surgery/therapy in persistent cases.
Critical periods / windows of opportunity: biceps recovery assessment at 3 months (surgical-decision window); primary nerve reconstruction generally within 3–9 months; glenohumeral remodeling after soft-tissue release is most reliable before ~5 years of age (PMID: 31085034, PMID: 8838992).

9. Inheritance and Population

Epidemiology: incidence ~0.9–1.5 per 1000 live births in administrative datasets, ~0.15/1000 in some declining national cohorts, up to 14.5/1000 by active surveillance (with 3.6/1000 persisting beyond 2 months) (PMID: 40315612, PMID: 39187951, PMID: 41616322). Incidence has declined over time in several countries (–47.6% in Germany 2005–2018) alongside rising cesarean rates and obstetric training.
Inheritance / penetrance / expressivity / anticipation / mosaicism / founder effects / carrier frequency: Not applicable — acquired, non-heritable condition.
Population demographics: no ethnic genetic predisposition; distribution tracks obstetric risk factors (macrosomia, maternal diabetes/obesity, birth-attendant practice, and access to cesarean delivery). Socioeconomic deprivation is associated with higher OBPP incidence (PMID: 37694876). No consistent sex predilection is established. Age distribution: by definition affected at birth; the prevalent chronic population comprises children/adults with residual deficits.

10. Diagnostics

Clinical examination (primary): characteristic waiter's-tip posture; assessment with Active Movement Scale and Mallet score; classification by Narakas grade (I–IV).
Imaging:
MRI (3T) — for root avulsion vs. rupture: mean sensitivity ~68%, specificity ~89% (PMID: 39432686, PMID: 41451467); useful but cannot solely guide surgical decisions. Pseudomeningocele is an unreliable avulsion marker.
CT myelography — alternative for avulsion assessment.
Ultrasound / MRI / CT — for glenohumeral dysplasia (glenoid version, % humeral head anterior to scapular line).
X-ray — to exclude clavicular/humeral fracture (differential and co-injury).
Electrophysiology: EMG and nerve conduction studies help characterize denervation, reinnervation, and prognosis; useful but must be interpreted cautiously in neonates.
Genetic testing (WGS/WES/panels/karyotype/CMA/FISH/mtDNA/repeat testing): Not applicable — no genetic basis; genetic testing has no diagnostic role.
Laboratory tests / biomarkers / omics diagnostics: Not applicable — no blood, metabolomic, proteomic, or molecular biomarker is used diagnostically.
Differential diagnosis: clavicular or humeral fracture (pseudoparalysis), septic shoulder/osteomyelitis, cerebral injury with hemiparesis, total (pan-plexus) palsy, Klumpke (lower-plexus) palsy, and — in older presentations — non-plexus conditions (a specialty clinic found ~7% of presumed BPI patients had a non-plexus condition; PMID: 40379206).
Screening: newborn physical examination is the effective "screen"; no carrier/genetic screening applies.

11. Outcome / Prognosis

Survival/mortality: Erb palsy is not life-threatening; survival is that of the general newborn population. Mortality is not disease-attributable.
Recovery: 80–95% recover spontaneously; the strongest positive prognostic factor is biceps (elbow-flexion) recovery by 3 months (PMID: 12874720, PMID: 8838992). Presence of shoulder dystocia and severe/avulsion injuries predict persistence (PMID: 40843939).
Morbidity/disability (persistent cases): shoulder internal-rotation contracture, glenohumeral dysplasia (~49%), limb-length discrepancy, muscle atrophy, cocontractions, elbow-flexion and forearm-supination deformities; functional limitation in bimanual tasks.
Prognostic factors: injury severity/extent (Narakas grade, root avulsion), timing of biceps recovery, presence of Horner syndrome (worse), and access to timely microsurgery.
Prognostic biomarkers: none molecular; serial clinical scoring (AMS/Mallet) and imaging of glenohumeral remodeling serve as functional prognostic measures.

12. Treatment

Staged, time-sensitive ladder (NCIT-style intervention terms in brackets):

Physiotherapy / occupational therapy — first-line to maintain passive ROM and prevent contractures. (NCIT: Physical Therapy; Occupational Therapy.)
Botulinum toxin A into internal rotators/co-contracting muscles — improves passive external rotation (~46° at 4 months), may defer tendon transfer; also used before tendon transfer without permanent muscle atrophy (PMID: 32753228, PMID: 36995203). (NCIT: Botulinum Toxin Therapy.)
Primary microsurgical nerve reconstruction — neuroma excision + nerve grafting ± neurotization when biceps recovery is absent by ~3–6 months; decision-analysis supports individualized timing (some model up to 12 months) (PMID: 8838992, PMID: 24483255, PMID: 32588706). (NCIT: Nerve Graft; Nerve Repair.)
Distal nerve transfers — spinal accessory → suprascapular; Oberlin (ulnar fascicle → biceps); medial pectoral → axillary; effective as primary treatment in Narakas I with structured pediatric rehab (PMID: 27543083, PMID: 41500917). (NCIT: Nerve Transfer.)
Secondary orthopedic procedures for residual deformity — subscapularis/anterior shoulder release (glenoid version −32°→−12°; PMID: 30981548); open subscapularis lengthening + joint relocation (durable remodeling at 10 yr; PMID: 31085034); arthroscopic release + conjoint tendon transfer (PMID: 40772960); latissimus dorsi/teres major tendon transfers; humeral derotation osteotomy; radioulnar synostosis for supination deformity (PMID: 42568170). (NCIT: Tendon Transfer; Osteotomy; Arthrodesis.)

Outcomes. A systematic review of 965 patients found nerve grafts/transfers produced significant long-term gains in shoulder, elbow, and wrist function, but no approach was universally superior and outcome heterogeneity limits comparison (PMID: 40958300). Pharmacotherapy is limited to botulinum toxin; there are no systemic drugs, gene therapies, cell therapies, RNA therapies, targeted therapies, or immunotherapies for this mechanical injury — those categories are not applicable. Pharmacogenomics: not applicable.

13. Prevention

Primary (obstetric): multi-professional shoulder-dystocia simulation training reduced brachial plexus injury at birth from 7.4% to 1.3% (PMID: 25688719); maternal glycemic control and weight management reduce macrosomia/dystocia (Grade A) (PMID: 27318182, PMID: 41365423); cesarean delivery for estimated fetal weight thresholds (e.g., >4500 g with diabetes, >5000 g without); judicious induction of labor for impending macrosomia (PMID: 38477187, PMID: 33972073).
Secondary: newborn examination for early detection and prompt referral to a multidisciplinary brachial plexus team.
Tertiary: physiotherapy, botulinum toxin, and timely surgery to prevent contracture/dysplasia.
Limits: 50–70% of shoulder dystocia occurs without identifiable risk factors, so prediction-based prevention is inherently capped (PMID: 27318182).
Immunization / genetic counseling / vector control: Not applicable.

14. Other Species / Natural Disease

Taxonomy affected (experimental): Rattus norvegicus (NCBI:txid10116) is the principal experimental species; humans (NCBI:txid9606) are the natural host.
Natural veterinary disease: Brachial plexus traction/avulsion injuries occur in companion animals (dogs, cats) — typically traumatic (road-traffic) rather than obstetric — and share the pathophysiology of nerve root avulsion and denervation. A specific obstetric Erb palsy analog is not a recognized distinct veterinary entity; the comparative value lies in shared nerve-injury/denervation mechanisms.
Comparative biology / evolutionary conservation: the neonatal rat model faithfully reproduces the human sequence of denervation → contracture → glenohumeral dysplasia, indicating conserved musculoskeletal-growth responses to denervation (PMID: 18343282, PMID: 29244216).
Transmission / zoonosis: Not applicable (non-infectious, mechanical).

15. Model Organisms

Model type: mammalian in vivo — neonatal rat (Sprague-Dawley/Wistar) brachial plexus injury (NBPI) model, created by C5–C6 neurotomy, crush, or selective neurectomy at postnatal day ~5 (an induced/surgical model, not genetic).
Genetic models: none (no gene to target); models are surgical/chemodenervation-based.
Phenotype recapitulation: high — 100% develop internal-rotation contracture within 4 weeks; progressive external-rotation loss; glenoid version changes; pseudoglenoid, subluxation, and humeral-head deformity mirror human glenohumeral dysplasia; gait/limb-function deficits correlate with deformity severity (PMID: 18343282, PMID: 25124991, PMID: 24388715, PMID: 29244216, PMID: 38263956).
Limitations: rodent shoulder biomechanics and quadrupedal loading differ from the human; the model does not reproduce the obstetric mechanism itself (it isolates the downstream denervation/contracture sequence); functional/QoL endpoints are not directly translatable.
Applications: dissecting denervation vs. muscle-imbalance contributions to contracture, testing chemodenervation timing, studying aberrant reinnervation/cocontractions, and evaluating surgical/rehabilitative interventions.

Mechanistic Model / Interpretation

  Shoulder dystocia / macrosomia / operative delivery
    │  (lateral neck traction ↑ head–shoulder angle)
    ▼
   Stretch injury of C5–C6 (± C7) roots / upper trunk
    │
┌───────────┴───────────────┐
   neuropraxia/mild            severe axonotmesis /
   axonotmesis                 rupture / AVULSION
│                            │
▼                            ▼
  spontaneous regeneration     incomplete + aberrant reinnervation
  (biceps by ~3 mo)                  │
│                   ┌────────┼─────────────┐
▼                   ▼        ▼             ▼
   RECOVERY (80–95%)   subscapularis  muscle     neuroma-in-
       denervation   imbalance   continuity →
       + impaired    (IR>ER)     misrouting →
       growth         │          COCONTRACTIONS
            └────┬─────┘
                 ▼
      SHOULDER INTERNAL-ROTATION CONTRACTURE
                 │
                 ▼
posterior humeral-head subluxation + glenoid
retroversion → GLENOHUMERAL DYSPLASIA (~49% of
permanent cases) → fixed deformity, limb undergrowth

The unifying interpretation is that Erb palsy is a single mechanical trigger with a bifurcating natural history. The favorable branch dominates numerically. The unfavorable branch is not primarily about the nerve failing to regenerate but about the downstream musculoskeletal consequences of denervation during active growth — a subscapularis that is denervated, atrophic, and growth-restricted, compounded by imbalance and misrouted reinnervation, deforms the growing glenohumeral joint. This is why treatment is a time-sensitive ladder: nerve-level interventions must occur before irreversible muscle/joint changes, and once dysplasia is established, orthopedic reconstruction targets the downstream deformity. Prevention, correspondingly, sits entirely upstream at the obstetric event.

Evidence Base

PMID	Contribution	Type
40315612	Erb palsy = 66.6% of OBPI; incidence trend –47.6%	Human, national cohort
39187951	Shoulder dystocia AOR 56.9; cesarean protective; ~0.9–1.1/1000	Human, KID database
41616322	Active surveillance incidence 14.5/1000 (3.6/1000 persistent)	Human, prospective
39411814	BMI, dystocia duration, operative delivery risk factors	Human, cohort
40239714	≥3 maneuvers double adverse outcomes; BPI aIRR 2.58	Human, cohort
31856038	Dystocia, macrosomia, gestational diabetes as top risks	Human, KID database
12874720	80–95% spontaneous recovery	Human, series
25509702	73% spontaneous recovery; natural history	Human, cohort
40843939	85.7% recovery; permanent cases all had dystocia	Human, prospective
8838992	3-month biceps criterion for surgery	Human, clinical
24483255	Decision analysis favoring delayed (12 mo) repair for QoL	Computational
32588706	Evidence review supporting nerve surgery when recovery delayed	Human, review
39432686	MRI sensitivity 68%/specificity 89% for avulsion (meta-analysis)	Human, meta-analysis
41451467	3T MRI accuracy 68% vs. surgery	Human, cohort
40828115	Narakas class ≠ MRI injury pattern; C6 most injured	Human, cohort
37503533	Shoulder dysplasia in 49% of permanent BPBI	Human, cohort
18343282	Rat model recapitulates contracture + dysplasia	Model organism
25124991	Subscapularis denervation causes contracture	Model organism
24388715	Muscle imbalance causes contracture	Model organism
38263956	Neuroma-in-continuity → aberrant reinnervation/cocontractions	Model organism
29244216	Glenoid deformity correlates with gait	Model organism
25688719	Dystocia training reduces BPI 7.4%→1.3%	Human, time-series
27318182	CNGOF guidelines; glycemic control; prevention limits	Guideline
32753228	Botulinum toxin improves IR contracture	Human, cohort
27543083	Distal nerve transfers as primary treatment	Human, series
41500917	DAFRA rehab; SAN–SSN 71.4% full ER	Human, series
30981548	Anterior shoulder release improves glenoid version	Human, cohort
31085034	Subscapularis lengthening; durable 10-yr remodeling	Human, cohort
42568170	Radioulnar synostosis for supination deformity	Human, series
40958300	Systematic review of 965 patients: nerve surgery gains	Human, systematic review
41913992	Current concepts: staged surgical ladder	Human, review
41588374	Defines overstretching of C5–T1 roots	Human, review
33904192	Neonatal anatomy/evolution as predisposing factors	Human, review
37694876	Deprivation associated with OBPP	Human, cohort
40379206	~7% of presumed BPI are non-plexus conditions	Human, cohort

Limitations and Knowledge Gaps

Incidence uncertainty. Estimates span an order of magnitude (0.15 to 14.5/1000) depending on ascertainment; administrative data undercount transient neuropraxia while active surveillance captures it. A standardized case definition and reporting mechanism is needed.
Surgical timing controversy. The 3-month biceps criterion (PMID: 8838992) conflicts with decision-analytic support for delay to 12 months (PMID: 24483255); no randomized trial exists, and evidence for nerve surgery vs. conservative management is Level IV at best (PMID: 32588706).
Outcome heterogeneity. The systematic review of 965 patients highlights inconsistent outcome measures (AMS vs. Mallet vs. others), precluding definitive comparison of nerve-graft vs. nerve-transfer superiority (PMID: 40958300).
Classification–anatomy mismatch. Narakas clinical grades do not reliably predict the true MRI/surgical injury pattern (PMID: 40828115), and MRI sensitivity for avulsion is only ~68% (PMID: 39432686).
Mechanism evidence is model-based. The denervation/muscle-imbalance/aberrant-reinnervation mechanisms are strongest in rat models; direct human molecular confirmation is limited.
QoL data gap. Erb-palsy-specific quality-of-life instrument data (EQ-5D/SF-36/PROMIS) are scarce; functional scores dominate.
Prevention ceiling. 50–70% of shoulder dystocia is unpredictable, limiting primary prevention (PMID: 27318182).

Proposed Follow-up Experiments / Actions

Multicenter prospective registry with a uniform case definition and standardized outcome set (AMS + Mallet + a validated pediatric QoL tool) to resolve incidence and outcome heterogeneity.
Randomized/pragmatic trial of surgical timing (early ~3 mo vs. delayed ~9–12 mo) stratified by injury severity and biceps recovery trajectory.
Prospective head-to-head comparison of primary distal nerve transfers vs. nerve grafting in Narakas I injuries.
Improved imaging — validate high-resolution/diffusion MRI or intraoperative electrophysiology to raise avulsion-detection sensitivity above the current ~68%.
Mechanistic translation — molecular/transcriptomic study of denervated human subscapularis at surgery to confirm rat-model growth-impairment pathways and identify anti-contracture drug targets.
Prevention effectiveness — evaluate scaled, mandatory shoulder-dystocia simulation training and its impact on population-level BPI rates, building on the Bristol interrupted time-series.

Report compiled from an autonomous, literature-grounded investigation (5 iterations, 8 confirmed findings, 42 papers reviewed). Erb palsy is characterized here as an acquired, non-genetic C5–C6 brachial plexus birth traction injury; template sections concerning heritable genetics, epigenetics, inheritance, infectious agents, and systemic/gene/cell/RNA/immuno-therapeutics are explicitly marked not applicable.

Artifacts

Reference Validation

Checked with linkml-reference-validator 0.2.1.

Outcome	Count
References checked	40
Resolved	40
Unresolved (possible confabulation)	0
Unverifiable	0
Quoted claims checked	9
Quoted claims found in source	9
Quoted claims not found in source	0
References weighed for topical relevance	40
On topic	31
Off topic	0

All extracted references resolved successfully.

Term Validation

Checked with linkml-term-validator 0.4.5, through the ols: adapter.

Outcome	Count
Terms checked	22
Resolved	22
Unresolved (possible confabulation)	0
Obsolete	0
Unverifiable	0
Terms whose name was checked	14
Terms named correctly	8
Terms named as a different term	3
Terms whose name is worth a second look	3

Terms the report names something else

These identifiers resolve, so nothing about them looks wrong, and the ontology calls them something unrelated to what the report calls them. That usually means the identifier is not the one the sentence needs:

HP:0001319 (1 mention) - the report calls it "approximate"; HP calls it Neonatal hypotonia
HP:0031843 (1 mention) - the report calls it "Shoulder contracture, approximate"; HP calls it Abnormally slow thought process
CL:0000138 (2 mentions) - the report calls it "chondrocyte, for glenoid remodeling"; CL calls it chondrocyte

Terms whose name is worth a second look

The report's name for these is recognisably related to the term's own name without being one of them. A loose paraphrase reads the same way as a citation of the wrong sibling term - and so does a related synonym, which the ontology records precisely because it names something adjacent rather than the same thing - so these are listed rather than judged:

HP:0011461 (1 mention) - the report calls it "neonatal-onset, approximate"; HP calls it Fetal onset
HP:0006633 (1 mention) - the report calls it "Glenoid dysplasia, approximate"; HP calls it Glenoid fossa hypoplasia, and lists "Glenoid hypoplasia" among its other names
CL:0000100 (3 mentions) - the report calls it "motor neuron", "Cell level: motor neurons/axons"; CL calls it motor neuron**

Terms named inconsistently

The report gives these identifiers more than one name of its own:

CL:0000100 - called "motor neuron", "Cell level:** motor neurons/axons"

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Discussions and Knowledge Gaps

Pathophysiology

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Phenotypes

Medical Actions

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Diagnosis

Prevalence

Differential Diagnoses

Animal Models

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References & Deep Research

References

Deep Research

Erb Palsy — Comprehensive Disease Characterization Report

Summary

Key Findings

Finding 1 — Erb palsy is the most common OBPI subtype; incidence ~0.9–1.5 per 1000 live births

Finding 2 — Shoulder dystocia is the strongest risk factor; cesarean delivery is protective

Finding 3 — Most cases recover spontaneously; surgery is indicated when biceps recovery is absent by 3–6 months

Finding 4 — Diagnosis is clinical (Narakas classification); MRI has modest sensitivity for avulsion; glenohumeral dysplasia is a major sequela

Finding 5 — Shoulder internal-rotation contracture arises from denervation-induced impaired subscapularis growth and muscle imbalance (rat models)

Finding 6 — Prevention is primarily obstetric: shoulder-dystocia simulation training and glycemic control reduce injury

Finding 7 — Treatment follows a staged ladder: physiotherapy → botulinum toxin → nerve reconstruction/transfers → secondary orthopedic procedures

Finding 8 — Integrated synthesis: Erb palsy as an acquired, non-genetic C5–C6 birth traction injury

Full Report by Section

1. Disease Information

2. Etiology

3. Phenotypes

4. Genetic / Molecular Information

5. Environmental Information

6. Mechanism / Pathophysiology

7. Anatomical Structures Affected

8. Temporal Development

9. Inheritance and Population

10. Diagnostics

11. Outcome / Prognosis

12. Treatment

13. Prevention

14. Other Species / Natural Disease

15. Model Organisms

Mechanistic Model / Interpretation

Evidence Base

Limitations and Knowledge Gaps

Proposed Follow-up Experiments / Actions

Artifacts

Reference Validation

Term Validation

Terms the report names something else

Terms whose name is worth a second look

Terms named inconsistently