Volumetric Muscle Loss

Traumatic Injury Pathograph 11 Show in embeddings browser Musculoskeletal Disease

Volumetric muscle loss (VML) is the traumatic or surgical loss of a large volume of skeletal muscle — frank ablation of muscle fibers together with the basal lamina, satellite cells, vasculature, and nerve of the defect — that exceeds the endogenous regenerative capacity of mammalian skeletal muscle. Rather than regenerating functional contractile tissue, the defect heals through an evolutionarily conserved wound-closure program that fills it with non-functional fibrotic scar, producing persistent strength deficits and disability. VML is common in civilian and military extremity trauma and often presents with a residual open wound. This entry models VML as an instance of the conserved fibrotic response specialized to skeletal muscle, and incorporates the spatial fibrosis-versus-myogenesis competition mechanism derived from the Wound Environment Agent-Based Model (WEABM) digital twin.

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7
Pathophys.
4
Phenotypes
2
Hypotheses
2
Gaps
11
Pathograph
7
Medical Actions
2
Trials
1
Deep Research
◈

Mechanistic Hypotheses

2
Canonical Evolutionarily-Conserved Fibrotic Wound-Closure Dominance
canonical_evolutionary_fibrotic_closure CANONICAL
The frank loss of muscle tissue in VML exceeds the regenerative capacity of skeletal muscle, so the defect is resolved by the evolutionarily conserved wound-healing imperative to rapidly close the wound. Inflammation and myofibroblast-driven collagen deposition fill the defect with fibrotic scar at the expense of de novo myofiber regeneration, yielding persistent functional deficits.
Pathograph links
Persistent Open-Wound Inflammatory Stimulus -> Myofibroblast Activation and Excessive Collagen Deposition DIRECT
Myofibroblast Activation and Excessive Collagen Deposition -> Excessive ECM Deposition DIRECT
Excessive ECM Deposition -> Fibrotic Scar Replacement and Persistent Functional Deficit DIRECT
Show evidence (2 references)
PMID:27825160 SUPPORT Other
"The frank loss of muscle tissue that defines VML injuries is beyond the robust reparative and regenerative capacities of mammalian skeletal muscle."
Establishes that VML exceeds endogenous regenerative capacity, the premise of the canonical fibrotic-closure model. Source is OTHER because this is a review synthesizing clinical and preclinical studies.
PMID:29030619 SUPPORT Model Organism
"VML injury incites an overwhelming inflammatory and fibrotic response that leads to expansive fibrous tissue deposition and chronic functional deficits, which ECM repair does not augment."
A porcine VML model demonstrates the dominant, treatment-resistant fibrotic response that defines the canonical mechanism.
Fibrosis-Myogenesis Spatial Competition for Myofibril-Edge Attachment Sites
fibrosis_myogenesis_spatial_competition EMERGING
A computationally derived mechanism (WEABM digital twin): fibrosis and myogenesis compete for a shared, spatially limited resource — the exposed edges of intact myofibrils where myoblasts must attach to nucleate fusion and differentiation. Collagen deposition that caps these myofibril ends precludes myoblast fusion, so the faster fibrotic program preempts regeneration. This reframes VML repair as a spatial control problem and predicts that promoting myogenesis alone is insufficient without simultaneously restraining fibrosis and closing the wound. Independent spatial-transcriptomics evidence (mouse and canine) supports the spatial premise: a pro-fibrotic program organized in space restricts muscle stem cell-mediated repair, and disrupting it increases regeneration while reducing fibrosis.
Pathograph links
Myofibroblast Activation and Excessive Collagen Deposition -> Fibrosis-Myogenesis Spatial Competition DIRECT
Impaired Satellite Cell-Mediated Myogenesis -> Fibrosis-Myogenesis Spatial Competition DIRECT
Fibrosis-Myogenesis Spatial Competition -> Fibrotic Scar Replacement and Persistent Functional Deficit DIRECT
Show evidence (2 references)
DOI:10.1101/2024.06.04.595972 SUPPORT Computational
"a competition between fibrosis and myogenesis due to spatial constraints on available edges of intact myofibrils to initiate the myoblast differentiation process"
The WEABM agent-based model identifies the spatial fibrosis-myogenesis competition as a fundamental emergent property of VML healing. Source is COMPUTATIONAL because the insight derives from in silico simulation.
DOI:10.1101/2022.06.03.494707 SUPPORT Model Organism
"This program was observed to restrict muscle stem cell mediated repair and targeting this circuit in a murine model resulted in increased regeneration and reductions in inflammation and fibrosis."
Spatial transcriptomics in mouse and canine VML provides independent in vivo evidence that the spatially organized pro-fibrotic program restricts stem-cell-mediated myogenesis, corroborating the WEABM competition hypothesis from experimental data.
?

Discussions and Knowledge Gaps

2
Volumetric muscle loss is an acquired traumatic/surgical entity that does not have a clean MONDO or OMIM disease term; should it be mapped to a broader muscle-injury concept, captured only as a phenotype, or recorded as a standalone curated entry without a disease_term until an appropriate ontology term exists?
KNOWLEDGE GAP OPEN gap_vml_no_mondo_term
Attached to
disease
dismech Disease entries normally carry a MONDO disease_term, but VML is an acquired injury phenotype rather than a classic nosological disease, so no suitable term was found at curation time. The entry is retained because VML has a coherent, well-described pathomechanism (conserved fibrotic response + fibrosis-myogenesis competition). Resolving the mapping would improve cross-referencing and classification.
Does the WEABM digital twin's in silico, canine-calibrated mechanism — in particular the fibrosis-myogenesis spatial competition and the multimodal adaptive control policy discovered by deep reinforcement learning — translate to human VML, and would the proposed sense-and-actuate device actually shift healing toward functional muscle in vivo?
KNOWLEDGE GAP OPEN gap_vml_weabm_translational_validity
Attached to
pathophysiology#Fibrosis-Myogenesis Spatial Competition mechanistic_hypotheses#fibrosis_myogenesis_spatial_competition
The competition mechanism and control strategy are emergent properties of an agent-based simulation calibrated to a canine VML model; they are leads, not validated human biology. The proposed multimodal device has not been built or tested. Confirming the mechanism and the control policy in vivo (and ultimately in humans) is required before the EMERGING hypothesis can be elevated.
Proposed experiments
Spatial fibrosis-myogenesis competition assay at the myofibril edge
in vivo regeneration assay
exp_vml_myofibril_edge_competition
In an animal VML model, use time-resolved histology/imaging to test whether collagen capping of exposed myofibril ends precludes subsequent myoblast fusion at those sites, and whether localized anti-fibrotic intervention increases the number of regeneration-competent myofibril edges.
Model systems
Rodent or porcine VML injury model
Standardized surgical VML defect with sequential sampling of the fibrotic and regenerative compartments at the defect margin.
OTHER
Closed-loop multimodal wound-control device trial
in vivo device intervention study
exp_vml_multimodal_control_device
Build and test a sense-and-actuate device implementing the WEABM-derived multimodal control (mediator modulation + engineered ECM wound closure + anti-fibrotic agent) in an animal VML model, measuring functional muscle recovery and scar fraction against standard care.
Model systems
Large-animal VML injury model
Clinically scaled VML defect permitting device placement, wound sensing, and longitudinal functional assessment.
OTHER
⚙

Pathophysiology

7
Frank Muscle Loss and Destruction of the Regenerative Niche
Traumatic or surgical ablation removes a large volume of skeletal muscle including the myofibers, basal lamina, and resident satellite cells of the defect, together with its vascular and neural supply. Because adult mammalian muscle cannot perform de novo myofiber regeneration across such a defect, the loss of the satellite-cell/basal-lamina niche initiates a dysregulated wound-healing program rather than restoration of contractile tissue. The residual open wound exposes the defect to the environment.
skeletal muscle satellite cell CL:0000594 skeletal muscle fiber CL:0008002
wound healing GO:0042060 ↕ DYSREGULATED skeletal muscle tissue regeneration GO:0043403 ↓ DECREASED
skeletal muscle tissue UBERON:0001134
Downstream
Persistent Open-Wound Inflammatory Stimulus
Skeletal muscle atrophy Frank loss of contractile tissue and destruction of the satellite-cell regenerative niche reduce muscle mass at and around the defect.
Show evidence (2 references)
PMID:27825160 SUPPORT Other
"The frank loss of muscle tissue that defines VML injuries is beyond the robust reparative and regenerative capacities of mammalian skeletal muscle."
Defines the initiating frank tissue loss that exceeds regenerative capacity. Source is OTHER because this is a clinical/preclinical review.
PMID:29030619 SUPPORT Model Organism
"VML injury presents a defect region in which all native elements required for canonical skeletal muscle regeneration (e.g., basal lamina and satellite cells) are removed"
Documents removal of the satellite-cell/basal-lamina regenerative niche that disables canonical regeneration in a porcine VML study.
Persistent Open-Wound Inflammatory Stimulus
The open VML wound, exposed to the atmospheric/environmental interface, acts as an ongoing source of damage-associated molecular patterns that recruit early neutrophils and activate macrophages, sustaining a chronic inflammatory response. This persistent inflammatory stimulus biases the wound toward the pro-fibrotic repair program: macrophage-to-mesenchymal progenitor crosstalk shifts toward TGF-beta in fibrotic conditions and toward PDGF in regenerative conditions, so the polarization of this crosstalk helps set the fibrotic-versus-regenerative outcome. The WEABM digital twin identifies biologically "closing" the wound as necessary to remove this self-renewing inflammatory drive.
Canonical Evolutionarily-Conserved Fibrotic Wound-Closure Dominance
macrophage CL:0000235 neutrophil CL:0000775
inflammatory response GO:0006954 ↑ INCREASED
skeletal muscle tissue UBERON:0001134
Downstream
Myofibroblast Activation and Excessive Collagen Deposition Canonical Evolutionarily-Conserved Fibrotic Wound-Closure Dominance
Impaired Satellite Cell-Mediated Myogenesis
Show evidence (3 references)
DOI:10.1101/2024.06.04.595972 SUPPORT Computational
"the wound from atmospheric/environmental exposure, which represents an ongoing inflammatory stimulus that promotes fibrosis"
The WEABM identifies the open-wound interface as a persistent pro-fibrotic inflammatory stimulus. Source is COMPUTATIONAL (in silico).
PMID:29030619 SUPPORT Model Organism
"VML injury incites an overwhelming inflammatory and fibrotic response that leads to expansive fibrous tissue deposition and chronic functional deficits, which ECM repair does not augment."
Confirms an overwhelming inflammatory response coupled to fibrosis in a porcine VML model.
DOI:10.1097/SLA.0000000000005704 SUPPORT Model Organism
"Receptor/ligand analysis of macrophage-to-mesenchymal progenitor cell crosstalk showed enhanced transforming growth factor β in fibrotic conditions and enhanced platelet-derived growth factor signaling in regenerative conditions."
Mouse single-cell analysis across musculoskeletal injuries shows that macrophage-to-mesenchymal crosstalk polarizes toward TGF-beta (fibrotic) versus PDGF (regenerative), identifying the inflammatory crosstalk that biases VML outcome. Preclinical (MODEL_ORGANISM).
Myofibroblast Activation and Excessive Collagen Deposition
Pro-fibrotic signaling (notably TGF-beta) activates resident fibroblasts to transdifferentiate into myofibroblasts that proliferate and deposit excessive collagen within and around the defect. In skeletal muscle the collagen- depositing cells arise largely from fibro-adipogenic progenitors (FAPs); a macrophage-FAP crosstalk circuit — sustained, aberrant M2-like and hybrid macrophages co-localizing with FAPs in areas of collagen deposition — drives the pro-fibrotic program in critical-size VML defects. This is the central fibrotic effector arm specialized from the conserved module to skeletal muscle, and it is the target of the WEABM-proposed anti-fibrotic intervention aimed at the collagen-producing function of fibroblasts and myofibroblasts.
Canonical Evolutionarily-Conserved Fibrotic Wound-Closure Dominance Fibrosis-Myogenesis Spatial Competition for Myofibril-Edge Attachment Sites
fibro-adipogenic progenitor (FAP) CL:0000057 myofibroblast CL:0000186 macrophage CL:0000235
TGF-beta receptor signaling pathway GO:0007179 ↑ INCREASED collagen biosynthetic process GO:0032964 ↑ INCREASED
Downstream
Fibrosis-Myogenesis Spatial Competition Fibrosis-Myogenesis Spatial Competition for Myofibril-Edge Attachment Sites
Excessive ECM Deposition Canonical Evolutionarily-Conserved Fibrotic Wound-Closure Dominance
Show evidence (3 references)
PMID:27825160 SUPPORT Other
"The limited clinical data available highlighted proliferative fibrosis secondary to VML injury as a viable target to improve limb range of motion."
Identifies proliferative fibrosis as a salient, targetable manifestation of VML. Source is OTHER because this is a clinical/preclinical review.
DOI:10.1101/2024.06.04.595972 SUPPORT Computational
"the administration of an anti-fibrotic agent focused on the collagen-producing function of fibroblasts and myofibroblasts"
The WEABM nominates fibroblast/myofibroblast collagen production as the effector to suppress, confirming this node as the central fibrotic arm.
DOI:10.1038/s42003-023-04790-6 SUPPORT Model Organism
"the retained M2-like macrophages from critical VML injuries presented with aberrant cytokine production which may contribute to fibrogenesis, as indicated by their co-localization with fibroadipogenic progenitors (FAPs) in areas of collagen deposition within the defect"
Murine single-cell/pseudo-time analysis localizes the FAP-driven collagen deposition to retained, aberrant M2-like macrophages, identifying the macrophage-FAP circuit as the cellular driver of the fibrotic effector arm.
Excessive ECM Deposition
Activated, FAP-derived myofibroblasts deposit excessive collagen (types I and III) and other matrix proteins while matrix turnover is outpaced, filling the defect with disorganized fibrotic matrix instead of functional contractile tissue. This is the matrix-accumulation effector step specialized from the conserved module to skeletal muscle.
Canonical Evolutionarily-Conserved Fibrotic Wound-Closure Dominance
myofibroblast CL:0000186
extracellular matrix organization GO:0030198 ↑ INCREASED collagen fibril organization GO:0030199 ↑ INCREASED
Downstream
Fibrotic Scar Replacement and Persistent Functional Deficit Canonical Evolutionarily-Conserved Fibrotic Wound-Closure Dominance
Skeletal muscle fibrosis Excessive collagen/ECM deposition within and around the defect manifests as skeletal muscle fibrosis.
Show evidence (2 references)
PMID:29030619 SUPPORT Model Organism
"leads to expansive fibrous tissue deposition and chronic functional deficits"
A porcine VML model documents expansive fibrous matrix deposition as the effector that fills the defect, the matrix-accumulation step of this node.
PMID:27825160 SUPPORT Other
"proliferative fibrosis secondary to VML injury as a viable target to improve limb range of motion"
A clinical/preclinical review identifies proliferative fibrosis (excess matrix) as the targetable accumulation in VML. Source is OTHER (review).
Impaired Satellite Cell-Mediated Myogenesis
The regenerative arm of the response: surviving satellite cells at the defect margin activate, proliferate into myoblasts, and attempt to fuse at the exposed edges of intact myofibrils to form new contractile tissue. In VML this program is quantitatively overwhelmed — both because the satellite-cell niche was ablated and because the available myofibril-edge attachment sites are limited and progressively lost to fibrosis.
Fibrosis-Myogenesis Spatial Competition for Myofibril-Edge Attachment Sites
skeletal muscle satellite cell CL:0000594 myoblast CL:0000056
satellite cell activation involved in skeletal muscle regeneration GO:0014901 ↓ DECREASED myoblast fusion GO:0007520 ↓ DECREASED
Downstream
Fibrosis-Myogenesis Spatial Competition Fibrosis-Myogenesis Spatial Competition for Myofibril-Edge Attachment Sites
Show evidence (1 reference)
DOI:10.1101/2024.06.04.595972 SUPPORT Computational
"a competition between fibrosis and myogenesis due to spatial constraints on available edges of intact myofibrils to initiate the myoblast differentiation process"
The WEABM shows myoblast differentiation/fusion is rate-limited by available myofibril edges, defining the regenerative arm and its bottleneck. Source is COMPUTATIONAL.
Fibrosis-Myogenesis Spatial Competition
The pivotal disease-specific mechanism: myogenesis and fibrosis compete for a shared, spatially limited resource — the exposed edges of intact myofibrils at the defect margin where myoblasts must attach to nucleate fusion. When collagen deposition caps these edges before myoblast fusion occurs, further regeneration at that site is precluded and the fibrotic program wins. Because fibrosis is evolutionarily favored for rapid wound closure, the default trajectory is scar; the WEABM predicts that only multimodal, adaptive control that simultaneously restrains fibrosis, closes the wound, and promotes myogenesis can shift this balance toward functional muscle.
Fibrosis-Myogenesis Spatial Competition for Myofibril-Edge Attachment Sites
myoblast fusion GO:0007520 ↓ DECREASED
Downstream
Fibrotic Scar Replacement and Persistent Functional Deficit Fibrosis-Myogenesis Spatial Competition for Myofibril-Edge Attachment Sites
Show evidence (1 reference)
DOI:10.1101/2024.06.04.595972 SUPPORT Computational
"selective, multimodal and adaptive local mediator-level control can shift the trajectory of healing away from a highly evolutionarily beneficial imperative to close the wound via fibrosis"
The WEABM frames the outcome as a controllable competition whose default is fibrotic closure, supporting this node as the decisive branch point.
Fibrotic Scar Replacement and Persistent Functional Deficit
The lost muscle volume is ultimately replaced by non-functional fibrous scar that infiltrates and distorts the residual musculature. The result is a chronic strength deficit that is disproportionately worse than the initial frank loss of contractile tissue — reflecting fibrosis, intramuscular nerve damage, architectural perturbation, and impaired force transmission in the remaining muscle — producing limb dysfunction and disability.
skeletal muscle tissue UBERON:0001134
Downstream
Muscle weakness Replacement of contractile tissue by non-functional scar and impaired force transmission produces a persistent, disproportionate strength deficit.
Limitation of joint mobility Fibrotic scar contracture and loss of contractile tissue across the injured muscle restrict range of motion at the spanned joint.
Show evidence (2 references)
DOI:10.1101/2024.06.04.595972 SUPPORT Computational
"replacement of the lost muscle mass with non-functional scar"
States the defining end-state of VML healing — scar replacing functional muscle. Source is COMPUTATIONAL (model paper abstract framing).
PMID:27825160 SUPPORT Other
"percent VML strength deficits are significantly worse than can be explained by the initial frank loss of contractile machinery"
Documents that the functional deficit exceeds what frank tissue loss alone predicts, the clinical consequence of this node.
⬡

Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.
Pathograph: causal mechanism network for Volumetric Muscle Loss Interactive directed graph showing how pathophysiology mechanisms, phenotypes, genetic factors and variants, experimental models, environmental triggers, and treatments relate through causal and linked edges.
●

Phenotypes

4
Musculoskeletal 3
Muscle weakness Muscle weakness HP:0001324
Course: STABLE
Show evidence (1 reference)
PMID:27825160 SUPPORT Other
"percent VML strength deficits are significantly worse than can be explained by the initial frank loss of contractile machinery"
Supports persistent, disproportionate strength deficit as a defining phenotype of VML.
Skeletal muscle atrophy Skeletal muscle atrophy HP:0003202
Show evidence (1 reference)
PMID:27825160 SUPPORT Other
"The frank loss of muscle tissue that defines VML injuries is beyond the robust reparative and regenerative capacities of mammalian skeletal muscle."
Supports irreversible loss of muscle tissue/mass as a core feature of VML.
Limitation of joint mobility Limitation of joint mobility HP:0001376
Show evidence (1 reference)
DOI:10.1038/npjregenmed.2016.8 SUPPORT Human Clinical
"by 6 months after ECM implantation, patients showed an average improvement of 37.3% (P<0.05) in strength and 27.1% improvement in range-of-motion tasks (P<0.05)"
Documented range-of-motion deficits (and their partial improvement with treatment) in a human VML cohort support reduced joint mobility as a phenotype.
Other 1
Skeletal muscle fibrosis Skeletal muscle fibrosis HP:0030951
Show evidence (1 reference)
PMID:29030619 SUPPORT Model Organism
"leads to expansive fibrous tissue deposition and chronic functional deficits"
A porcine VML model documents expansive fibrous tissue replacing muscle, supporting skeletal muscle fibrosis as a defining phenotype.
💊

Medical Actions

7
Surgical Reconstruction
Action: surgical procedure MAXO:0000004
Reconstructive surgery for large muscle defects, including free functional muscle transfer and debridement, to restore bulk and function.
Decellularized ECM Scaffold Implantation
Action: surgical procedure MAXO:0000004
Implantation of acellular biological scaffolds (decellularized extracellular matrices) into the defect, typically combined with aggressive early physical therapy, to support host remodeling. Evidence is mixed: an open-label 13-patient human cohort reported modest strength and range-of-motion gains, whereas controlled animal studies show ECM repair does not reverse the dominant fibrotic response, and meta-analysis finds the overall regenerative benefit small.
Show evidence (3 references)
DOI:10.1038/npjregenmed.2016.8 SUPPORT Human Clinical
"by 6 months after ECM implantation, patients showed an average improvement of 37.3% (P<0.05) in strength and 27.1% improvement in range-of-motion tasks (P<0.05)"
A 13-patient human cohort study reports measurable strength and range-of-motion improvement after ECM bioscaffold implantation with physical therapy.
PMID:29030619 PARTIAL Model Organism
"VML injury incites an overwhelming inflammatory and fibrotic response that leads to expansive fibrous tissue deposition and chronic functional deficits, which ECM repair does not augment."
A porcine VML model shows ECM scaffold repair does not overcome the fibrotic response, tempering expectations for this treatment.
DOI:10.1089/ten.teb.2019.0207 PARTIAL Other
"an acellular biomaterial in combination with cellular components was the most effective treatment to improve functional capacity following VML injury to date"
A systematic review and meta-analysis of animal VML studies finds acellular biomaterials (especially with cells) the most effective class, though the overall benefit is small. Source is OTHER (meta-analysis of animal studies).
Physical Therapy and Rehabilitation
Action: physical therapy MAXO:0000011
Rehabilitation to preserve range of motion and maximize function of the remaining musculature after VML.
WEABM Digital-Twin-Directed Multimodal Wound Control (Investigational)
Action: therapeutic procedure Ontology label: Therapeutic Procedure NCIT:C49236
A computationally proposed (not yet clinically tested) cyber-physical device that integrates wound sensing with multimodal, adaptive delivery of mediators to mitigate inflammation and pro-fibrotic compensatory anti-inflammation, promote myogenesis, biologically close the wound with an engineered ECM, and administer an anti-fibrotic agent targeting fibroblast/myofibroblast collagen production.
Show evidence (1 reference)
DOI:10.1101/2024.06.04.595972 SUPPORT Computational
"the administration of an anti-fibrotic agent focused on the collagen-producing function of fibroblasts and myofibroblasts"
Describes one of the WEABM-derived design principles for the proposed multimodal control device. Source is COMPUTATIONAL; the device is investigational and not yet validated in vivo or in humans.
IL-10 Local Immunotherapy (Investigational)
Action: Pharmacotherapy NCIT:C15986
Agent: recombinant interleukin-10 NCIT:C1320
Preclinical immunotherapy delivering recombinant IL-10 locally at the VML repair site (delayed dosing). In a rat tibialis anterior model combined with minced-muscle repair, IL-10 improved contractile torque, muscle mass, and myofiber size, likely via regulatory T-cell recruitment. Not yet tested in humans.
Show evidence (1 reference)
DOI:10.1038/s41598-023-27981-x SUPPORT Model Organism
"significant improvements to TA contractile torque (82% of uninjured values & 170% of PBS values), TA mass, and myofiber size in response to IL-10 treatment were detected"
A rat VML model shows delayed local IL-10 immunotherapy improves contractile function and muscle mass. Preclinical (MODEL_ORGANISM).
Maresin 1 Pro-Resolving Lipid Mediator Therapy (Investigational)
Action: Pharmacotherapy NCIT:C15986
Agent: Maresin 1 CHEBI:138249
Preclinical immuno-regenerative therapy using Maresin 1, a specialized pro-resolving lipid mediator derived from docosahexaenoic acid, to counter the pro-inflammatory eicosanoid imbalance of non-healing VML. In a mouse VML model it reduced fibrosis and inflammatory infiltrate and improved strength recovery. Not yet tested in humans.
Show evidence (1 reference)
DOI:10.7554/eLife.86437 SUPPORT Model Organism
"Treatment of VML with a pro-resolving lipid mediator synthesized from docosahexaenoic acid, called Maresin 1, ameliorated fibrosis through reduction of neutrophils and macrophages and enhanced recovery of muscle strength."
A mouse VML model shows the pro-resolving mediator Maresin 1 reduces fibrosis and improves strength. Preclinical (MODEL_ORGANISM).
TGF-beta Receptor (TGFBR2) Inhibition (Investigational)
Action: Pharmacotherapy NCIT:C15986
Preclinical anti-fibrotic strategy targeting the macrophage-FAP pro-fibrotic circuit via TGFBR2 inhibition. In a murine VML model, disrupting this circuit increased muscle stem cell-mediated regeneration and reduced inflammation and fibrosis. Not yet tested in humans.
Show evidence (1 reference)
DOI:10.1101/2022.06.03.494707 SUPPORT Model Organism
"targeting this circuit in a murine model resulted in increased regeneration and reductions in inflammation and fibrosis"
Spatial-transcriptomics-guided disruption of the macrophage-FAP circuit (via TGFBR2 inhibition) improves regeneration in a murine VML model. Preclinical (MODEL_ORGANISM).
🔬

Clinical Trials

2
NCT01292876 COMPLETED
Musculotendinous Tissue Unit Repair and Reinforcement (MTURR) using decellularized ECM biologic scaffolds for severe skeletal muscle injury at the University of Pittsburgh (17 subjects); the trial from which the Dziki et al. 13-patient ECM cohort analysis was drawn.
Target Phenotypes: Muscle weakness HP:0001324 Limitation of joint mobility HP:0001376
Show evidence (1 reference)
clinicaltrials:NCT01292876 SUPPORT Human Clinical
"This study formally evaluated healing and return of function after an extracellular matrix device implantation in 17 male and female subjects"
The trial record describes the ECM-scaffold VML repair cohort underlying the Dziki et al. functional-outcome study.
NCT04051242 TERMINATED
Single-center University of Pittsburgh study of the XenMatrix AB surgical graft for restoration of function in volumetric muscle loss after soft tissue trauma; terminated (10 subjects enrolled).
Target Phenotypes: Muscle weakness HP:0001324
Show evidence (1 reference)
clinicaltrials:NCT04051242 SUPPORT Human Clinical
"in the restoration of function in the setting of volumetric muscle loss after soft tissue trauma"
The trial record confirms an ECM/xenograft surgical approach to functional restoration in VML; the study was terminated.
{ }

Source YAML

click to show 
name: Volumetric Muscle Loss
creation_date: "2026-06-12T00:00:00Z"
category: Traumatic Injury
parents:
- Musculoskeletal Disease
description: >-
  Volumetric muscle loss (VML) is the traumatic or surgical loss of a large
  volume of skeletal muscle — frank ablation of muscle fibers together with the
  basal lamina, satellite cells, vasculature, and nerve of the defect — that
  exceeds the endogenous regenerative capacity of mammalian skeletal muscle.
  Rather than regenerating functional contractile tissue, the defect heals
  through an evolutionarily conserved wound-closure program that fills it with
  non-functional fibrotic scar, producing persistent strength deficits and
  disability. VML is common in civilian and military extremity trauma and often
  presents with a residual open wound. This entry models VML as an instance of
  the conserved fibrotic response specialized to skeletal muscle, and
  incorporates the spatial fibrosis-versus-myogenesis competition mechanism
  derived from the Wound Environment Agent-Based Model (WEABM) digital twin.
synonyms:
- VML
- volumetric muscle loss injury
notes: >-
  No MONDO/OMIM disease term currently maps cleanly to volumetric muscle loss as
  an acquired traumatic entity, so disease_term is intentionally omitted (see the
  curation-gap discussion). VML conforms to the fibrotic_response module:
  pathophysiology nodes substitute skeletal-muscle-specific cell types
  (satellite cell, myoblast, skeletal muscle fiber) for the generic module
  cell types while preserving the conserved injury -> inflammation ->
  mesenchymal/myofibroblast activation -> excessive ECM -> organ dysfunction
  causal chain. The disease-specific addition is the spatial competition between
  fibrosis and myogenesis for the limited exposed edges of intact myofibrils
  required to nucleate myoblast fusion.

mechanistic_hypotheses:
- hypothesis_group_id: canonical_evolutionary_fibrotic_closure
  hypothesis_label: Canonical Evolutionarily-Conserved Fibrotic Wound-Closure Dominance
  status: CANONICAL
  description: >-
    The frank loss of muscle tissue in VML exceeds the regenerative capacity of
    skeletal muscle, so the defect is resolved by the evolutionarily conserved
    wound-healing imperative to rapidly close the wound. Inflammation and
    myofibroblast-driven collagen deposition fill the defect with fibrotic scar
    at the expense of de novo myofiber regeneration, yielding persistent
    functional deficits.
  evidence:
  - reference: PMID:27825160
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      The frank loss of muscle tissue that defines VML injuries is beyond the
      robust reparative and regenerative capacities of mammalian skeletal muscle.
    explanation: >-
      Establishes that VML exceeds endogenous regenerative capacity, the premise
      of the canonical fibrotic-closure model. Source is OTHER because this is a
      review synthesizing clinical and preclinical studies.
  - reference: PMID:29030619
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      VML injury incites an overwhelming inflammatory and fibrotic response that
      leads to expansive fibrous tissue deposition and chronic functional
      deficits, which ECM repair does not augment.
    explanation: >-
      A porcine VML model demonstrates the dominant, treatment-resistant fibrotic
      response that defines the canonical mechanism.
- hypothesis_group_id: fibrosis_myogenesis_spatial_competition
  hypothesis_label: Fibrosis-Myogenesis Spatial Competition for Myofibril-Edge Attachment Sites
  status: EMERGING
  description: >-
    A computationally derived mechanism (WEABM digital twin): fibrosis and
    myogenesis compete for a shared, spatially limited resource — the exposed
    edges of intact myofibrils where myoblasts must attach to nucleate fusion and
    differentiation. Collagen deposition that caps these myofibril ends precludes
    myoblast fusion, so the faster fibrotic program preempts regeneration. This
    reframes VML repair as a spatial control problem and predicts that promoting
    myogenesis alone is insufficient without simultaneously restraining fibrosis
    and closing the wound. Independent spatial-transcriptomics evidence (mouse
    and canine) supports the spatial premise: a pro-fibrotic program organized in
    space restricts muscle stem cell-mediated repair, and disrupting it increases
    regeneration while reducing fibrosis.
  evidence:
  - reference: DOI:10.1101/2024.06.04.595972
    supports: SUPPORT
    evidence_source: COMPUTATIONAL
    snippet: >-
      a competition between fibrosis and myogenesis due to spatial constraints on
      available edges of intact myofibrils to initiate the myoblast
      differentiation process
    explanation: >-
      The WEABM agent-based model identifies the spatial fibrosis-myogenesis
      competition as a fundamental emergent property of VML healing. Source is
      COMPUTATIONAL because the insight derives from in silico simulation.
  - reference: DOI:10.1101/2022.06.03.494707
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      This program was observed to restrict muscle stem cell mediated repair and
      targeting this circuit in a murine model resulted in increased regeneration
      and reductions in inflammation and fibrosis.
    explanation: >-
      Spatial transcriptomics in mouse and canine VML provides independent in
      vivo evidence that the spatially organized pro-fibrotic program restricts
      stem-cell-mediated myogenesis, corroborating the WEABM competition
      hypothesis from experimental data.

pathophysiology:
- name: Frank Muscle Loss and Destruction of the Regenerative Niche
  description: >-
    Traumatic or surgical ablation removes a large volume of skeletal muscle
    including the myofibers, basal lamina, and resident satellite cells of the
    defect, together with its vascular and neural supply. Because adult mammalian
    muscle cannot perform de novo myofiber regeneration across such a defect, the
    loss of the satellite-cell/basal-lamina niche initiates a dysregulated
    wound-healing program rather than restoration of contractile tissue. The
    residual open wound exposes the defect to the environment.
  conforms_to: "fibrotic_response#Tissue Injury"
  role: trigger
  cell_types:
  - preferred_term: skeletal muscle satellite cell
    term:
      id: CL:0000594
      label: skeletal muscle satellite cell
  - preferred_term: skeletal muscle fiber
    term:
      id: CL:0008002
      label: skeletal muscle fiber
  locations:
  - preferred_term: skeletal muscle tissue
    term:
      id: UBERON:0001134
      label: skeletal muscle tissue
  biological_processes:
  - preferred_term: wound healing
    term:
      id: GO:0042060
      label: wound healing
    modifier: DYSREGULATED
  - preferred_term: skeletal muscle tissue regeneration
    term:
      id: GO:0043403
      label: skeletal muscle tissue regeneration
    modifier: DECREASED
  evidence:
  - reference: PMID:27825160
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      The frank loss of muscle tissue that defines VML injuries is beyond the
      robust reparative and regenerative capacities of mammalian skeletal muscle.
    explanation: >-
      Defines the initiating frank tissue loss that exceeds regenerative
      capacity. Source is OTHER because this is a clinical/preclinical review.
  - reference: PMID:29030619
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      VML injury presents a defect region in which all native elements required
      for canonical skeletal muscle regeneration (e.g., basal lamina and
      satellite cells) are removed
    explanation: >-
      Documents removal of the satellite-cell/basal-lamina regenerative niche
      that disables canonical regeneration in a porcine VML study.
  downstream:
  - target: Persistent Open-Wound Inflammatory Stimulus
    causal_link_type: DIRECT
  - target: Skeletal muscle atrophy
    description: >-
      Frank loss of contractile tissue and destruction of the satellite-cell
      regenerative niche reduce muscle mass at and around the defect.
    causal_link_type: DIRECT

- name: Persistent Open-Wound Inflammatory Stimulus
  description: >-
    The open VML wound, exposed to the atmospheric/environmental interface, acts
    as an ongoing source of damage-associated molecular patterns that recruit
    early neutrophils and activate macrophages, sustaining a chronic
    inflammatory response. This persistent inflammatory stimulus biases the
    wound toward the pro-fibrotic repair program: macrophage-to-mesenchymal
    progenitor crosstalk shifts toward TGF-beta in fibrotic conditions and
    toward PDGF in regenerative conditions, so the polarization of this crosstalk
    helps set the fibrotic-versus-regenerative outcome. The WEABM digital twin
    identifies biologically "closing" the wound as necessary to remove this
    self-renewing inflammatory drive.
  conforms_to: "fibrotic_response#Inflammatory Recruitment and Amplification"
  role: amplifier
  cell_types:
  - preferred_term: macrophage
    term:
      id: CL:0000235
      label: macrophage
  - preferred_term: neutrophil
    term:
      id: CL:0000775
      label: neutrophil
  locations:
  - preferred_term: skeletal muscle tissue
    term:
      id: UBERON:0001134
      label: skeletal muscle tissue
  biological_processes:
  - preferred_term: inflammatory response
    term:
      id: GO:0006954
      label: inflammatory response
    modifier: INCREASED
  evidence:
  - reference: DOI:10.1101/2024.06.04.595972
    supports: SUPPORT
    evidence_source: COMPUTATIONAL
    snippet: >-
      the wound from atmospheric/environmental exposure, which represents an
      ongoing inflammatory stimulus that promotes fibrosis
    explanation: >-
      The WEABM identifies the open-wound interface as a persistent
      pro-fibrotic inflammatory stimulus. Source is COMPUTATIONAL (in silico).
  - reference: PMID:29030619
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      VML injury incites an overwhelming inflammatory and fibrotic response that
      leads to expansive fibrous tissue deposition and chronic functional
      deficits, which ECM repair does not augment.
    explanation: >-
      Confirms an overwhelming inflammatory response coupled to fibrosis in a
      porcine VML model.
  - reference: DOI:10.1097/SLA.0000000000005704
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Receptor/ligand analysis of macrophage-to-mesenchymal progenitor cell
      crosstalk showed enhanced transforming growth factor β in fibrotic
      conditions and enhanced platelet-derived growth factor signaling in
      regenerative conditions.
    explanation: >-
      Mouse single-cell analysis across musculoskeletal injuries shows that
      macrophage-to-mesenchymal crosstalk polarizes toward TGF-beta (fibrotic)
      versus PDGF (regenerative), identifying the inflammatory crosstalk that
      biases VML outcome. Preclinical (MODEL_ORGANISM).
  downstream:
  - target: Myofibroblast Activation and Excessive Collagen Deposition
    causal_link_type: DIRECT
    hypothesis_groups:
    - canonical_evolutionary_fibrotic_closure
  - target: Impaired Satellite Cell-Mediated Myogenesis
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES

- name: Myofibroblast Activation and Excessive Collagen Deposition
  description: >-
    Pro-fibrotic signaling (notably TGF-beta) activates resident fibroblasts to
    transdifferentiate into myofibroblasts that proliferate and deposit excessive
    collagen within and around the defect. In skeletal muscle the collagen-
    depositing cells arise largely from fibro-adipogenic progenitors (FAPs); a
    macrophage-FAP crosstalk circuit — sustained, aberrant M2-like and hybrid
    macrophages co-localizing with FAPs in areas of collagen deposition — drives
    the pro-fibrotic program in critical-size VML defects. This is the central
    fibrotic effector arm specialized from the conserved module to skeletal
    muscle, and it is the target of the WEABM-proposed anti-fibrotic intervention
    aimed at the collagen-producing function of fibroblasts and myofibroblasts.
  conforms_to: "fibrotic_response#Mesenchymal Cell Activation"
  role: central_effector
  cell_types:
  - preferred_term: fibro-adipogenic progenitor (FAP)
    term:
      id: CL:0000057
      label: fibroblast
  - preferred_term: myofibroblast
    term:
      id: CL:0000186
      label: myofibroblast cell
  - preferred_term: macrophage
    term:
      id: CL:0000235
      label: macrophage
  biological_processes:
  - preferred_term: TGF-beta receptor signaling pathway
    term:
      id: GO:0007179
      label: transforming growth factor beta receptor signaling pathway
    modifier: INCREASED
  - preferred_term: collagen biosynthetic process
    term:
      id: GO:0032964
      label: collagen biosynthetic process
    modifier: INCREASED
  evidence:
  - reference: PMID:27825160
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      The limited clinical data available highlighted proliferative fibrosis
      secondary to VML injury as a viable target to improve limb range of motion.
    explanation: >-
      Identifies proliferative fibrosis as a salient, targetable manifestation of
      VML. Source is OTHER because this is a clinical/preclinical review.
  - reference: DOI:10.1101/2024.06.04.595972
    supports: SUPPORT
    evidence_source: COMPUTATIONAL
    snippet: >-
      the administration of an anti-fibrotic agent focused on the
      collagen-producing function of fibroblasts and myofibroblasts
    explanation: >-
      The WEABM nominates fibroblast/myofibroblast collagen production as the
      effector to suppress, confirming this node as the central fibrotic arm.
  - reference: DOI:10.1038/s42003-023-04790-6
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      the retained M2-like macrophages from critical VML injuries presented with
      aberrant cytokine production which may contribute to fibrogenesis, as
      indicated by their co-localization with fibroadipogenic progenitors (FAPs)
      in areas of collagen deposition within the defect
    explanation: >-
      Murine single-cell/pseudo-time analysis localizes the FAP-driven collagen
      deposition to retained, aberrant M2-like macrophages, identifying the
      macrophage-FAP circuit as the cellular driver of the fibrotic effector arm.
  downstream:
  - target: Fibrosis-Myogenesis Spatial Competition
    causal_link_type: DIRECT
    hypothesis_groups:
    - fibrosis_myogenesis_spatial_competition
  - target: Excessive ECM Deposition
    causal_link_type: DIRECT
    hypothesis_groups:
    - canonical_evolutionary_fibrotic_closure

- name: Excessive ECM Deposition
  description: >-
    Activated, FAP-derived myofibroblasts deposit excessive collagen (types I and
    III) and other matrix proteins while matrix turnover is outpaced, filling the
    defect with disorganized fibrotic matrix instead of functional contractile
    tissue. This is the matrix-accumulation effector step specialized from the
    conserved module to skeletal muscle.
  conforms_to: "fibrotic_response#Excessive ECM Deposition"
  role: effector
  cell_types:
  - preferred_term: myofibroblast
    term:
      id: CL:0000186
      label: myofibroblast cell
  biological_processes:
  - preferred_term: extracellular matrix organization
    term:
      id: GO:0030198
      label: extracellular matrix organization
    modifier: INCREASED
  - preferred_term: collagen fibril organization
    term:
      id: GO:0030199
      label: collagen fibril organization
    modifier: INCREASED
  evidence:
  - reference: PMID:29030619
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      leads to expansive fibrous tissue deposition and chronic functional
      deficits
    explanation: >-
      A porcine VML model documents expansive fibrous matrix deposition as the
      effector that fills the defect, the matrix-accumulation step of this node.
  - reference: PMID:27825160
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      proliferative fibrosis secondary to VML injury as a viable target to
      improve limb range of motion
    explanation: >-
      A clinical/preclinical review identifies proliferative fibrosis (excess
      matrix) as the targetable accumulation in VML. Source is OTHER (review).
  downstream:
  - target: Fibrotic Scar Replacement and Persistent Functional Deficit
    causal_link_type: DIRECT
    hypothesis_groups:
    - canonical_evolutionary_fibrotic_closure
  - target: Skeletal muscle fibrosis
    description: >-
      Excessive collagen/ECM deposition within and around the defect manifests
      as skeletal muscle fibrosis.
    causal_link_type: DIRECT

- name: Impaired Satellite Cell-Mediated Myogenesis
  description: >-
    The regenerative arm of the response: surviving satellite cells at the defect
    margin activate, proliferate into myoblasts, and attempt to fuse at the
    exposed edges of intact myofibrils to form new contractile tissue. In VML
    this program is quantitatively overwhelmed — both because the satellite-cell
    niche was ablated and because the available myofibril-edge attachment sites
    are limited and progressively lost to fibrosis.
  role: effector
  cell_types:
  - preferred_term: skeletal muscle satellite cell
    term:
      id: CL:0000594
      label: skeletal muscle satellite cell
  - preferred_term: myoblast
    term:
      id: CL:0000056
      label: myoblast
  biological_processes:
  - preferred_term: satellite cell activation involved in skeletal muscle regeneration
    term:
      id: GO:0014901
      label: satellite cell activation involved in skeletal muscle regeneration
    modifier: DECREASED
  - preferred_term: myoblast fusion
    term:
      id: GO:0007520
      label: myoblast fusion
    modifier: DECREASED
  evidence:
  - reference: DOI:10.1101/2024.06.04.595972
    supports: SUPPORT
    evidence_source: COMPUTATIONAL
    snippet: >-
      a competition between fibrosis and myogenesis due to spatial constraints on
      available edges of intact myofibrils to initiate the myoblast
      differentiation process
    explanation: >-
      The WEABM shows myoblast differentiation/fusion is rate-limited by
      available myofibril edges, defining the regenerative arm and its
      bottleneck. Source is COMPUTATIONAL.
  downstream:
  - target: Fibrosis-Myogenesis Spatial Competition
    causal_link_type: DIRECT
    hypothesis_groups:
    - fibrosis_myogenesis_spatial_competition

- name: Fibrosis-Myogenesis Spatial Competition
  description: >-
    The pivotal disease-specific mechanism: myogenesis and fibrosis compete for a
    shared, spatially limited resource — the exposed edges of intact myofibrils
    at the defect margin where myoblasts must attach to nucleate fusion. When
    collagen deposition caps these edges before myoblast fusion occurs, further
    regeneration at that site is precluded and the fibrotic program wins. Because
    fibrosis is evolutionarily favored for rapid wound closure, the default
    trajectory is scar; the WEABM predicts that only multimodal, adaptive control
    that simultaneously restrains fibrosis, closes the wound, and promotes
    myogenesis can shift this balance toward functional muscle.
  role: central_effector
  biological_processes:
  - preferred_term: myoblast fusion
    term:
      id: GO:0007520
      label: myoblast fusion
    modifier: DECREASED
  evidence:
  - reference: DOI:10.1101/2024.06.04.595972
    supports: SUPPORT
    evidence_source: COMPUTATIONAL
    snippet: >-
      selective, multimodal and adaptive local mediator-level control can shift
      the trajectory of healing away from a highly evolutionarily beneficial
      imperative to close the wound via fibrosis
    explanation: >-
      The WEABM frames the outcome as a controllable competition whose default is
      fibrotic closure, supporting this node as the decisive branch point.
  downstream:
  - target: Fibrotic Scar Replacement and Persistent Functional Deficit
    causal_link_type: DIRECT
    hypothesis_groups:
    - fibrosis_myogenesis_spatial_competition

- name: Fibrotic Scar Replacement and Persistent Functional Deficit
  description: >-
    The lost muscle volume is ultimately replaced by non-functional fibrous scar
    that infiltrates and distorts the residual musculature. The result is a
    chronic strength deficit that is disproportionately worse than the initial
    frank loss of contractile tissue — reflecting fibrosis, intramuscular nerve
    damage, architectural perturbation, and impaired force transmission in the
    remaining muscle — producing limb dysfunction and disability.
  conforms_to: "fibrotic_response#Architectural Distortion and Organ Dysfunction"
  role: consequence
  locations:
  - preferred_term: skeletal muscle tissue
    term:
      id: UBERON:0001134
      label: skeletal muscle tissue
  evidence:
  - reference: DOI:10.1101/2024.06.04.595972
    supports: SUPPORT
    evidence_source: COMPUTATIONAL
    snippet: >-
      replacement of the lost muscle mass with non-functional scar
    explanation: >-
      States the defining end-state of VML healing — scar replacing functional
      muscle. Source is COMPUTATIONAL (model paper abstract framing).
  - reference: PMID:27825160
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      percent VML strength deficits are significantly worse than can be explained
      by the initial frank loss of contractile machinery
    explanation: >-
      Documents that the functional deficit exceeds what frank tissue loss alone
      predicts, the clinical consequence of this node.
  downstream:
  - target: Muscle weakness
    description: >-
      Replacement of contractile tissue by non-functional scar and impaired force
      transmission produces a persistent, disproportionate strength deficit.
    causal_link_type: DIRECT
  - target: Limitation of joint mobility
    description: >-
      Fibrotic scar contracture and loss of contractile tissue across the injured
      muscle restrict range of motion at the spanned joint.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - Fibrotic scar contracture limiting muscle excursion

phenotypes:
- name: Muscle weakness
  description: >-
    Persistent loss of muscle strength in the affected limb after VML, worse than
    predicted by the volume of tissue lost.
  phenotype_term:
    preferred_term: Muscle weakness
    term:
      id: HP:0001324
      label: Muscle weakness
    clinical_course: STABLE
  evidence:
  - reference: PMID:27825160
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      percent VML strength deficits are significantly worse than can be explained
      by the initial frank loss of contractile machinery
    explanation: >-
      Supports persistent, disproportionate strength deficit as a defining
      phenotype of VML.
- name: Skeletal muscle atrophy
  description: >-
    Loss of muscle mass at and around the defect, compounded by replacement of
    contractile tissue with fibrotic scar.
  phenotype_term:
    preferred_term: Skeletal muscle atrophy
    term:
      id: HP:0003202
      label: Skeletal muscle atrophy
  evidence:
  - reference: PMID:27825160
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      The frank loss of muscle tissue that defines VML injuries is beyond the
      robust reparative and regenerative capacities of mammalian skeletal muscle.
    explanation: >-
      Supports irreversible loss of muscle tissue/mass as a core feature of VML.
- name: Limitation of joint mobility
  description: >-
    Reduced range of motion across the joint spanned by the injured muscle, due to
    loss of contractile tissue and fibrotic scar contracture; partially reversible
    with treatment.
  phenotype_term:
    preferred_term: Limitation of joint mobility
    term:
      id: HP:0001376
      label: Limitation of joint mobility
  evidence:
  - reference: DOI:10.1038/npjregenmed.2016.8
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      by 6 months after ECM implantation, patients showed an average improvement
      of 37.3% (P<0.05) in strength and 27.1% improvement in range-of-motion
      tasks (P<0.05)
    explanation: >-
      Documented range-of-motion deficits (and their partial improvement with
      treatment) in a human VML cohort support reduced joint mobility as a
      phenotype.
- name: Skeletal muscle fibrosis
  description: >-
    Replacement of contractile muscle by fibrous connective tissue within and
    around the defect — the defining pathological outcome of critical VML.
  phenotype_term:
    preferred_term: Skeletal muscle fibrosis
    term:
      id: HP:0030951
      label: Skeletal muscle fibrosis
  evidence:
  - reference: PMID:29030619
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      leads to expansive fibrous tissue deposition and chronic functional
      deficits
    explanation: >-
      A porcine VML model documents expansive fibrous tissue replacing muscle,
      supporting skeletal muscle fibrosis as a defining phenotype.

treatments:
- name: Surgical Reconstruction
  description: >-
    Reconstructive surgery for large muscle defects, including free functional
    muscle transfer and debridement, to restore bulk and function.
  treatment_term:
    preferred_term: surgical procedure
    term:
      id: MAXO:0000004
      label: surgical procedure
- name: Decellularized ECM Scaffold Implantation
  description: >-
    Implantation of acellular biological scaffolds (decellularized extracellular
    matrices) into the defect, typically combined with aggressive early physical
    therapy, to support host remodeling. Evidence is mixed: an open-label 13-patient
    human cohort reported modest strength and range-of-motion gains, whereas
    controlled animal studies show ECM repair does not reverse the dominant
    fibrotic response, and meta-analysis finds the overall regenerative benefit
    small.
  treatment_term:
    preferred_term: surgical procedure
    term:
      id: MAXO:0000004
      label: surgical procedure
  evidence:
  - reference: DOI:10.1038/npjregenmed.2016.8
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      by 6 months after ECM implantation, patients showed an average improvement
      of 37.3% (P<0.05) in strength and 27.1% improvement in range-of-motion
      tasks (P<0.05)
    explanation: >-
      A 13-patient human cohort study reports measurable strength and
      range-of-motion improvement after ECM bioscaffold implantation with
      physical therapy.
  - reference: PMID:29030619
    supports: PARTIAL
    evidence_source: MODEL_ORGANISM
    snippet: >-
      VML injury incites an overwhelming inflammatory and fibrotic response that
      leads to expansive fibrous tissue deposition and chronic functional
      deficits, which ECM repair does not augment.
    explanation: >-
      A porcine VML model shows ECM scaffold repair does not overcome the
      fibrotic response, tempering expectations for this treatment.
  - reference: DOI:10.1089/ten.teb.2019.0207
    supports: PARTIAL
    evidence_source: OTHER
    snippet: >-
      an acellular biomaterial in combination with cellular components was the
      most effective treatment to improve functional capacity following VML
      injury to date
    explanation: >-
      A systematic review and meta-analysis of animal VML studies finds acellular
      biomaterials (especially with cells) the most effective class, though the
      overall benefit is small. Source is OTHER (meta-analysis of animal studies).
- name: Physical Therapy and Rehabilitation
  description: >-
    Rehabilitation to preserve range of motion and maximize function of the
    remaining musculature after VML.
  treatment_term:
    preferred_term: physical therapy
    term:
      id: MAXO:0000011
      label: physical therapy
- name: WEABM Digital-Twin-Directed Multimodal Wound Control (Investigational)
  description: >-
    A computationally proposed (not yet clinically tested) cyber-physical device
    that integrates wound sensing with multimodal, adaptive delivery of mediators
    to mitigate inflammation and pro-fibrotic compensatory anti-inflammation,
    promote myogenesis, biologically close the wound with an engineered ECM, and
    administer an anti-fibrotic agent targeting fibroblast/myofibroblast collagen
    production.
  treatment_term:
    preferred_term: therapeutic procedure
    term:
      id: NCIT:C49236
      label: Therapeutic Procedure
  evidence:
  - reference: DOI:10.1101/2024.06.04.595972
    supports: SUPPORT
    evidence_source: COMPUTATIONAL
    snippet: >-
      the administration of an anti-fibrotic agent focused on the
      collagen-producing function of fibroblasts and myofibroblasts
    explanation: >-
      Describes one of the WEABM-derived design principles for the proposed
      multimodal control device. Source is COMPUTATIONAL; the device is
      investigational and not yet validated in vivo or in humans.
- name: IL-10 Local Immunotherapy (Investigational)
  description: >-
    Preclinical immunotherapy delivering recombinant IL-10 locally at the VML
    repair site (delayed dosing). In a rat tibialis anterior model combined with
    minced-muscle repair, IL-10 improved contractile torque, muscle mass, and
    myofiber size, likely via regulatory T-cell recruitment. Not yet tested in
    humans.
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: recombinant interleukin-10
      term:
        id: NCIT:C1320
        label: Recombinant Interleukin 10
  evidence:
  - reference: DOI:10.1038/s41598-023-27981-x
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      significant improvements to TA contractile torque (82% of uninjured values
      & 170% of PBS values), TA mass, and myofiber size in response to IL-10
      treatment were detected
    explanation: >-
      A rat VML model shows delayed local IL-10 immunotherapy improves
      contractile function and muscle mass. Preclinical (MODEL_ORGANISM).
- name: Maresin 1 Pro-Resolving Lipid Mediator Therapy (Investigational)
  description: >-
    Preclinical immuno-regenerative therapy using Maresin 1, a specialized
    pro-resolving lipid mediator derived from docosahexaenoic acid, to counter
    the pro-inflammatory eicosanoid imbalance of non-healing VML. In a mouse VML
    model it reduced fibrosis and inflammatory infiltrate and improved strength
    recovery. Not yet tested in humans.
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: Maresin 1
      term:
        id: CHEBI:138249
        label: (7R,14S)-dihydroxy-(4Z,8E,10E,12Z,16Z,19Z)-docosahexaenoic acid
  evidence:
  - reference: DOI:10.7554/eLife.86437
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Treatment of VML with a pro-resolving lipid mediator synthesized from
      docosahexaenoic acid, called Maresin 1, ameliorated fibrosis through
      reduction of neutrophils and macrophages and enhanced recovery of muscle
      strength.
    explanation: >-
      A mouse VML model shows the pro-resolving mediator Maresin 1 reduces
      fibrosis and improves strength. Preclinical (MODEL_ORGANISM).
- name: TGF-beta Receptor (TGFBR2) Inhibition (Investigational)
  description: >-
    Preclinical anti-fibrotic strategy targeting the macrophage-FAP pro-fibrotic
    circuit via TGFBR2 inhibition. In a murine VML model, disrupting this circuit
    increased muscle stem cell-mediated regeneration and reduced inflammation and
    fibrosis. Not yet tested in humans.
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
  evidence:
  - reference: DOI:10.1101/2022.06.03.494707
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      targeting this circuit in a murine model resulted in increased regeneration
      and reductions in inflammation and fibrosis
    explanation: >-
      Spatial-transcriptomics-guided disruption of the macrophage-FAP circuit
      (via TGFBR2 inhibition) improves regeneration in a murine VML model.
      Preclinical (MODEL_ORGANISM).

clinical_trials:
- name: NCT01292876
  status: COMPLETED
  description: >-
    Musculotendinous Tissue Unit Repair and Reinforcement (MTURR) using
    decellularized ECM biologic scaffolds for severe skeletal muscle injury at
    the University of Pittsburgh (17 subjects); the trial from which the Dziki
    et al. 13-patient ECM cohort analysis was drawn.
  target_phenotypes:
  - preferred_term: Muscle weakness
    term:
      id: HP:0001324
      label: Muscle weakness
  - preferred_term: Limitation of joint mobility
    term:
      id: HP:0001376
      label: Limitation of joint mobility
  evidence:
  - reference: clinicaltrials:NCT01292876
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      This study formally evaluated healing and return of function after an
      extracellular matrix device implantation in 17 male and female subjects
    explanation: >-
      The trial record describes the ECM-scaffold VML repair cohort underlying
      the Dziki et al. functional-outcome study.
- name: NCT04051242
  status: TERMINATED
  description: >-
    Single-center University of Pittsburgh study of the XenMatrix AB surgical
    graft for restoration of function in volumetric muscle loss after soft
    tissue trauma; terminated (10 subjects enrolled).
  target_phenotypes:
  - preferred_term: Muscle weakness
    term:
      id: HP:0001324
      label: Muscle weakness
  evidence:
  - reference: clinicaltrials:NCT04051242
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      in the restoration of function in the setting of volumetric muscle loss
      after soft tissue trauma
    explanation: >-
      The trial record confirms an ECM/xenograft surgical approach to functional
      restoration in VML; the study was terminated.

discussions:
- discussion_id: gap_vml_no_mondo_term
  prompt: >-
    Volumetric muscle loss is an acquired traumatic/surgical entity that does not
    have a clean MONDO or OMIM disease term; should it be mapped to a broader
    muscle-injury concept, captured only as a phenotype, or recorded as a
    standalone curated entry without a disease_term until an appropriate ontology
    term exists?
  kind: KNOWLEDGE_GAP
  status: OPEN
  attaches_to:
  - disease
  rationale: >-
    dismech Disease entries normally carry a MONDO disease_term, but VML is an
    acquired injury phenotype rather than a classic nosological disease, so no
    suitable term was found at curation time. The entry is retained because VML
    has a coherent, well-described pathomechanism (conserved fibrotic response +
    fibrosis-myogenesis competition). Resolving the mapping would improve
    cross-referencing and classification.
- discussion_id: gap_vml_weabm_translational_validity
  prompt: >-
    Does the WEABM digital twin's in silico, canine-calibrated mechanism — in
    particular the fibrosis-myogenesis spatial competition and the multimodal
    adaptive control policy discovered by deep reinforcement learning — translate
    to human VML, and would the proposed sense-and-actuate device actually shift
    healing toward functional muscle in vivo?
  kind: KNOWLEDGE_GAP
  status: OPEN
  attaches_to:
  - pathophysiology#Fibrosis-Myogenesis Spatial Competition
  - mechanistic_hypotheses#fibrosis_myogenesis_spatial_competition
  rationale: >-
    The competition mechanism and control strategy are emergent properties of an
    agent-based simulation calibrated to a canine VML model; they are leads, not
    validated human biology. The proposed multimodal device has not been built or
    tested. Confirming the mechanism and the control policy in vivo (and
    ultimately in humans) is required before the EMERGING hypothesis can be
    elevated.
  proposed_experiments:
  - experiment_id: exp_vml_myofibril_edge_competition
    name: Spatial fibrosis-myogenesis competition assay at the myofibril edge
    description: >-
      In an animal VML model, use time-resolved histology/imaging to test whether
      collagen capping of exposed myofibril ends precludes subsequent myoblast
      fusion at those sites, and whether localized anti-fibrotic intervention
      increases the number of regeneration-competent myofibril edges.
    experiment_type:
      preferred_term: in vivo regeneration assay
    model_systems:
    - name: Rodent or porcine VML injury model
      description: >-
        Standardized surgical VML defect with sequential sampling of the
        fibrotic and regenerative compartments at the defect margin.
      experimental_model_type: OTHER
  - experiment_id: exp_vml_multimodal_control_device
    name: Closed-loop multimodal wound-control device trial
    description: >-
      Build and test a sense-and-actuate device implementing the WEABM-derived
      multimodal control (mediator modulation + engineered ECM wound closure +
      anti-fibrotic agent) in an animal VML model, measuring functional muscle
      recovery and scar fraction against standard care.
    experiment_type:
      preferred_term: in vivo device intervention study
    model_systems:
    - name: Large-animal VML injury model
      description: >-
        Clinically scaled VML defect permitting device placement, wound sensing,
        and longitudinal functional assessment.
      experimental_model_type: OTHER
📚

References & Deep Research

Deep Research

1
Falcon ▸
1. Disease Information
Edison Scientific Literature 34 citations 2026-06-12T23:13:40.477597

1. Disease Information

1.1 Concise overview (current understanding)

Volumetric muscle loss (VML) is most commonly defined clinically as “the traumatic or surgical loss of skeletal muscle with resultant functional impairment.” (grogan2011volumetricmuscleloss pages 1-3, greising2019therapeuticapproachesfor pages 6-8). A key distinguishing feature is that VML represents tissue loss beyond typical skeletal muscle regenerative capacity, producing chronic functional deficits and disability (greising2019therapeuticapproachesfor pages 3-5, gahlawat2024tissueengineered3d pages 1-3).

Operational definitions vary across publications and settings: - A biomaterials paper describes VML as “a loss of over ~10% of muscle mass that results in functional impairment.” (Patel 2019; publication date Apr 2019; https://doi.org/10.1088/1748-605x/ab0b06) (patel2019alignednanofibersof pages 1-5). - A 2024 review cites a frequently used translational threshold: “When the loss of skeletal muscle exceeds 20%, the innate capacity for repair and regeneration is permanently compromised.” (Gahlawat 2024; publication date Jul 2024; https://doi.org/10.1007/s10439-024-03541-w) (gahlawat2024tissueengineered3d pages 1-3). - A ClinicalTrials.gov protocol (NCT04051242; 2020 posting) required both: structural deficit ≥20% of muscle-group mass and functional deficit ≥25% versus contralateral limb (NCT04051242 chunk 2).

1.2 Synonyms / alternative names

The dominant term in the retrieved literature is “volumetric muscle loss” / “VML.” Many sources also frame it as critical-sized skeletal muscle defect or critical VML versus subcritical defects that can regenerate (e.g., size-threshold models) (hymel2023identifyingdysregulatedimmune pages 1-2, chowdary2023macrophagemediatedpdgfactivation pages 1-3).

1.3 Data provenance

Most mechanistic knowledge is derived from aggregated preclinical models (murine/rat VML defects with defined sizes) and integrated -omics studies, with limited but important human cohort evidence for certain scaffold-based approaches (greising2019therapeuticapproachesfor pages 1-3, larouche2023spatiotemporalmappingof pages 1-3, dziki2016anacellularbiologic pages 1-2).

2. Etiology

2.1 Disease causal factors (primary causes)

VML arises from severe trauma (e.g., blast or crush injury) and/or surgical removal of skeletal muscle (e.g., resection after injury or oncologic surgery), producing large, abrupt loss of muscle tissue and architectural cues (gahlawat2024tissueengineered3d pages 1-3, grogan2011volumetricmuscleloss pages 1-3, greising2019therapeuticapproachesfor pages 3-5).

2.2 Risk factors

The key “risk factor” for VML is exposure to injury mechanisms that create large muscle voids (e.g., combat blast trauma, high-energy extremity injuries, complex open fractures with soft-tissue loss) (gahlawat2024tissueengineered3d pages 1-3, grogan2011volumetricmuscleloss pages 1-3).

  • Military context: VML is described as disproportionately common among military personnel and estimated to comprise ~50% of combat-related injuries in one 2024 review synthesis (Gahlawat 2024; Jul 2024; https://doi.org/10.1007/s10439-024-03541-w) (gahlawat2024tissueengineered3d pages 1-3).
  • Explosion-related extremity wounds: In OEF/OIF, extremity wounds were the majority of injuries, and “more than 75%” were due to explosions (Grogan & Hsu 2011; Feb 2011; https://doi.org/10.5435/00124635-201102001-00007) (grogan2011volumetricmuscleloss pages 1-3).

2.3 Protective factors / gene–environment interactions

No protective genetic variants or gene–environment interactions were identified in the retrieved VML-focused sources for this run. This aligns with VML being primarily a trauma phenotype rather than an inherited disease entity.

3. Phenotypes

3.1 Core phenotypes (symptoms/signs)

Commonly reported clinical and biological manifestations include: - Persistent muscle weakness / reduced force generation, chronic functional deficit (greising2019therapeuticapproachesfor pages 3-5, gahlawat2024tissueengineered3d pages 1-3). - Structural muscle void with replacement by fibrotic tissue / scar, impaired range of motion and task performance (dziki2016anacellularbiologic pages 1-2, larouche2023spatiotemporalmappingof pages 1-3). - Chronic inflammation and fibrosis, with regenerative failure (greising2019therapeuticapproachesfor pages 3-5, hymel2023identifyingdysregulatedimmune pages 1-2, larouche2023spatiotemporalmappingof pages 1-3).

3.2 Severity, progression, frequency

  • Onset pattern: Typically acute at injury/surgery.
  • Course: Often chronic deficits due to incomplete restoration of contractile tissue and persistent fibrosis (greising2019therapeuticapproachesfor pages 3-5, larouche2023spatiotemporalmappingof pages 1-3).
  • Severity thresholding: Animal and translational literature uses size/percent-loss thresholds (e.g., >~10%, >20%, or millimeter-scale defects) to define subcritical vs critical, nonhealing VML (patel2019alignednanofibersof pages 1-5, gahlawat2024tissueengineered3d pages 1-3, chowdary2023macrophagemediatedpdgfactivation pages 1-3).

3.3 Quality of life impact

VML is framed as causing long-term disability and loss of function, with significant impact in civilian and military trauma populations (patel2019alignednanofibersof pages 1-5, grogan2011volumetricmuscleloss pages 1-3).

3.4 Suggested HPO terms (examples)

(Recommendations based on phenotype descriptions in retrieved sources) - Muscle weakness: HP:0001324 - Abnormal muscle morphology (muscle tissue loss/atrophy): HP:0003202 (Muscular atrophy) - Decreased joint range of motion: HP:0001376 - Fibrosis (muscle): may map to broader fibrosis phenotypes such as HP:0002206 (Pulmonary fibrosis is organ-specific; HPO fibrosis terms vary by tissue—use tissue-specific fibrosis term if available).

4. Genetic / Molecular Information

4.1 Causal genes / variants

VML is not primarily a Mendelian genetic disease; no causal genes/variants were identified in the retrieved sources.

4.2 Molecular mediators implicated (not inherited “causal genes”)

Recent mechanistic studies emphasize signaling axes that shape regenerative vs fibrotic outcomes: - TGF-β signaling / TGFBR2: spatial transcriptomics + scRNA-seq indicated a pro-fibrotic program; pharmacologic inhibition of TGFBR2 increased MuSC infiltration into the defect and reduced inflammatory/fibrotic transcripts, improving regeneration (Larouche 2023; Jun 2023; https://doi.org/10.1101/2022.06.03.494707) (larouche2023spatiotemporalmappingof pages 1-3). - PDGF vs TGF-β as regenerative vs fibrotic correlates: single-cell analysis across injury models found enhanced TGF-β signaling in fibrotic conditions and enhanced PDGF signaling in regenerative conditions, with macrophage subtypes (fibrotic-like vs regenerative-like) better predicting outcome than classic M1/M2 polarization (Chowdary 2023; Sep 2023; https://doi.org/10.1097/SLA.0000000000005704) (chowdary2023macrophagemediatedpdgfactivation pages 1-3). - IL-10 signaling / Treg axis: delayed local IL-10 delivery after VML repair improved torque and increased ST2 (Treg receptor) expression at repair site (Huynh 2023; Feb 2023; https://doi.org/10.1038/s41598-023-27981-x) (huynh2023localil10delivery pages 1-2).

5. Environmental Information

VML is primarily driven by external injury mechanisms (blast, crush, complex open fractures, surgical resection). No toxin/radiation/pollution-specific environmental etiologies were identified in the retrieved VML-focused sources.

6. Mechanism / Pathophysiology

6.1 High-level causal chain

Trigger: acute traumatic/surgical excision of skeletal muscle → loss of myofibers, satellite cells, and native ECM scaffolding → altered immune dynamics and impaired structural guidance for regeneration → persistent inflammation and macrophage–mesenchymal progenitor crosstalk → excess collagen deposition/fibrosis and reduced vascular/nerve integration → chronic weakness and functional impairment (greising2019therapeuticapproachesfor pages 3-5, larouche2023spatiotemporalmappingof pages 1-3, hymel2023identifyingdysregulatedimmune pages 1-2).

A 2019 systematic review summarizes key mechanisms for failure of regeneration after VML: loss of resident satellite cells, loss of native extracellular matrix organization cues, and dysregulated/prolonged pro-inflammatory programs promoting fibrous tissue accumulation (greising2019therapeuticapproachesfor pages 3-5).

6.2 Immune dysregulation and fibrosis (2023–2024 advances)

Macrophage–FAP/MDC circuit and spatial restriction - In murine + canine VML, spatial transcriptomics integrated with scRNA-seq showed the defect zone enriched for inflammatory and collagen genes (e.g., Ctss/S100a8/S100a9 and Col1a1/Col1a2), while myogenic developmental genes were localized to a transition zone; MuSCs were largely confined to transition zone rather than infiltrating the defect, consistent with spatially restricted regeneration (larouche2023spatiotemporalmappingof pages 1-3). - A 2023 Communications Biology study found critical VML (3 mm) displayed sustained M2-like and CD206hiLy6Chi hybrid macrophages with aberrant cytokine production that co-localized with fibroadipogenic progenitors (FAPs) in collagen deposition regions; multiple T-cell subpopulations were elevated and the immune response failed to resolve into a pro-regenerative microenvironment within the first week (hymel2023identifyingdysregulatedimmune pages 1-2).

Defect-size thresholds and immune programs - Cross-study scRNA-seq analysis across musculoskeletal injuries identified that smaller VML defects regenerate while larger defects fibrose (size thresholds reported as <2 mm regenerative vs >3 mm fibrotic in that analysis framework) (chowdary2023macrophagemediatedpdgfactivation pages 1-3).

Lipid mediator imbalance and pro-resolving therapeutics - A 2023 eLife study profiled lipid mediators and found degenerative VML showed increased pro-inflammatory eicosanoids (e.g., LTB4, PGE2, PGF2α) with insufficient increases in pro-resolving mediators; replenishing Maresin 1 reduced neutrophils/macrophages, attenuated fibrosis, increased MuSC activation, and improved force recovery (Castor-Macias 2023; Dec 2023; https://doi.org/10.7554/eLife.86437) (castormacias2023maresin1repletion pages 9-11, castormacias2023maresin1repletion pages 2-5).

Immunotherapy: IL-10 - In a rat VML model repaired with minced muscle, delayed local recombinant IL-10 dosing from 7–14 days post-injury improved contractile outcomes at 56 days (torque 82% of uninjured; 170% of PBS controls) and induced IL-10 signaling and lymphocyte pathway signatures at 14 days (huynh2023localil10delivery pages 1-2).

6.3 Suggested GO biological process terms (examples)

  • Muscle tissue regeneration (GO:0055001)
  • Skeletal muscle satellite cell activation / myoblast differentiation (e.g., myoblast differentiation GO:0045445)
  • Inflammatory response (GO:0006954)
  • Macrophage activation (GO:0042116)
  • Extracellular matrix organization (GO:0030198)
  • Collagen fibril organization / fibrosis-related processes (e.g., collagen fibril organization GO:0030199)
  • Transforming growth factor beta receptor signaling pathway (GO:0007179)
  • Platelet-derived growth factor receptor signaling pathway (GO:0048008)

6.4 Suggested Cell Ontology (CL) terms (examples)

  • Skeletal muscle satellite cell / muscle stem cell (MuSC): skeletal muscle satellite cell (CL term; commonly used)
  • Macrophage: macrophage (CL:0000235)
  • Neutrophil: neutrophil (CL:0000775)
  • T cell / regulatory T cell: T cell (CL:0000084), regulatory T cell (CL:0000815)
  • Fibro-adipogenic progenitor / mesenchymal stromal progenitor: map to mesenchymal stromal cell / fibroblast progenitor terms depending on ontology availability

7. Anatomical Structures Affected

7.1 Organ/tissue

Primary tissue: skeletal muscle (e.g., extremity muscle compartments such as quadriceps, tibialis anterior, posterior compartment muscles) (hymel2023identifyingdysregulatedimmune pages 1-2, huynh2023localil10delivery pages 1-2).

7.2 Suggested UBERON terms (examples)

  • Skeletal muscle tissue: UBERON:0001134
  • Lower limb muscle / hindlimb muscle: appropriate limb-region UBERON terms depending on injury site

8. Temporal Development

8.1 Onset

Typically immediate/acute at the time of trauma or surgery (grogan2011volumetricmuscleloss pages 1-3).

8.2 Progression

  • Early inflammatory phase that fails to resolve in critical VML, evolving into chronic fibrosis with persistent functional deficits (hymel2023identifyingdysregulatedimmune pages 1-2, larouche2023spatiotemporalmappingof pages 1-3).

9. Inheritance and Population

9.1 Epidemiology / burden (available quantitative statistics)

Quantitative population incidence/prevalence per 100,000 was not found in the retrieved sources for this run (and may be difficult to quantify due to underreporting and coding/billing limitations) (gahlawat2024tissueengineered3d pages 1-3).

However, burden statistics in authoritative reviews include: - ~50% of combat-related injuries in military populations (review synthesis) (gahlawat2024tissueengineered3d pages 1-3). - In OEF/OIF, extremity wounds were the majority of soldier injuries and >75% were due to explosions (grogan2011volumetricmuscleloss pages 1-3). - Type-III open tibia fractures (with severe bone and soft tissue injury context) were associated with a reported 65% incidence of permanent disability/medical retirement (gahlawat2024tissueengineered3d pages 1-3).

9.2 Genetics / inheritance

Not applicable as a primary disease mechanism.

10. Diagnostics

10.1 Clinical assessment and outcome measures

There is no standardized protocol for characterizing/quantifying VML; recommended clinical documentation includes photographs/video, range-of-motion measurements, manual muscle strength testing, and isokinetic muscle function testing (Grogan & Hsu 2011; Feb 2011; https://doi.org/10.5435/00124635-201102001-00007) (grogan2011volumetricmuscleloss pages 1-3).

10.2 Imaging and tissue assessment (human cohort/trials)

In the 13-patient cohort using ECM scaffolds, imaging (CT/MRI pre-op and ~7 months post-op) assessed volumetric loss and fatty infiltration; ultrasound-guided biopsies were sampled at ~6 and 26 weeks; electrodiagnostics were performed in 8/13 subjects (Dziki 2016; Jul 2016; https://doi.org/10.1038/npjregenmed.2016.8) (dziki2016anacellularbiologic pages 10-10).

10.3 Trial-based operational diagnostic thresholds

NCT04051242 used: structural deficit ≥20% muscle-group mass and functional deficit ≥25% vs contralateral limb (ClinicalTrials.gov; 2020; https://clinicaltrials.gov/study/NCT04051242) (NCT04051242 chunk 2).

11. Outcome / Prognosis

11.1 Functional prognosis

VML is associated with persistent functional deficits because ablated myofibers do not regenerate and fibrosis replaces contractile tissue in critical injuries (greising2019therapeuticapproachesfor pages 3-5, larouche2023spatiotemporalmappingof pages 1-3). Functional deficits may exceed those predicted by mass loss alone (gahlawat2024tissueengineered3d pages 1-3).

11.2 Human outcome data (ECM scaffold cohort)

Dziki et al. reported that by 6 months after ECM implantation with aggressive physical therapy, patients showed average improvements vs pre-operative performance of 37.3% in strength and 27.1% in range-of-motion tasks (both P<0.05) (Dziki 2016; Jul 2016; https://doi.org/10.1038/npjregenmed.2016.8; NCT01292876) (dziki2016anacellularbiologic pages 1-2).

11.3 Evidence caveats

A 2019 systematic review noted limited human evidence and reported case reports with minimal net strength deficit improvement after acellular biomaterial repair in two service members (72%→~68% deficit at 4 months; 89%→~87% deficit at ~6 months), emphasizing that some “functional gains” may not reflect true muscle regeneration (greising2019therapeuticapproachesfor pages 14-16).

12. Treatment

12.1 Current applications / real-world implementations (standard of care)

Clinical management frequently includes: - Soft-tissue reconstruction (clinical gold standard): functional free muscle transfer and/or fasciocutaneous flaps, with limitations including donor-site morbidity and incomplete functional restoration (gahlawat2024tissueengineered3d pages 1-3). - Orthotics/bracing (including advanced bracing designs; carbon fiber-based braces described in 2024 review) and physical therapy as supportive care, though not correcting underlying strength deficits in many cases (grogan2011volumetricmuscleloss pages 1-3, gahlawat2024tissueengineered3d pages 1-3).

12.2 Regenerative medicine / advanced therapeutics (current state)

Acellular ECM bioscaffolds (human evidence) - Dziki et al. (2016) described a 13-patient cohort receiving ECM bioscaffolds plus aggressive early physical therapy with improved strength and ROM at 6 months and evidence of vascularized/innervated islands of skeletal muscle (dziki2016anacellularbiologic pages 1-2).

Clinical trials - NCT01292876: registered for the 13-patient ECM cohort described by Dziki et al. (2016) (dziki2016anacellularbiologic pages 1-2). - NCT04051242: “Enhanced Bioscaffold for Volumetric Muscle Loss” testing XENMATRIX AB™; includes explicit structural/functional inclusion criteria; status terminated; record notes two participants received the graft (ClinicalTrials.gov; 2020; https://clinicaltrials.gov/study/NCT04051242) (NCT04051242 chunk 2).

Immunomodulatory / immuno-regenerative strategies (preclinical, 2023) - IL-10 therapy improved contractile torque to 82% of uninjured values (and 170% of PBS controls) in a rat VML model (Huynh 2023; Feb 2023; https://doi.org/10.1038/s41598-023-27981-x) (huynh2023localil10delivery pages 1-2). - Maresin 1 (DHA-derived pro-resolving mediator) reduced fibrosis and improved strength after degenerative VML in mice (Castor-Macias 2023; Dec 2023; https://doi.org/10.7554/eLife.86437) (castormacias2023maresin1repletion pages 9-11). - Anti-fibrotic pathway targeting: inhibition of TGFBR2 increased MuSC infiltration and reduced inflammatory/fibrotic signatures (Larouche 2023; Jun 2023; https://doi.org/10.1101/2022.06.03.494707) (larouche2023spatiotemporalmappingof pages 1-3).

Expert synthesis / meta-analysis (animal evidence) A systematic review/meta-analysis found that in animal models, treatments improved functional capacity versus untreated controls with pooled effect size Hedges’ g = 0.75 (95% CI 0.53–0.96; p<1e-7), but authors emphasized the ~16% average beneficial effect was small and current paradigms require maturation; network meta-analysis suggested acellular biomaterial + stem/progenitor cells as the most effective tested class (Greising 2019; Dec 2019; https://doi.org/10.1089/ten.teb.2019.0207) (greising2019therapeuticapproachesfor pages 1-3).

12.3 MAXO term suggestions (examples)

  • Surgical tissue transfer / reconstruction (e.g., free functional muscle transfer): MAXO:0000004 (surgical procedure; use more specific MAXO if available)
  • Physical therapy / rehabilitation: MAXO term for rehabilitation therapy (ontology-dependent)
  • Orthotic device use/bracing: MAXO term for orthotic intervention
  • Implantation of biological scaffold / biomaterial implant: MAXO term for implantation of medical device/biomaterial
  • Cytokine therapy (IL-10): MAXO term for cytokine therapy

13. Prevention

Primary prevention is mainly trauma prevention (combat injury mitigation, occupational/vehicular safety). No specific biomedical prophylaxis is established in the retrieved VML-focused sources.

14. Other Species / Natural Disease

Not applicable as a naturally occurring transmissible disease; however, mechanistic and translational studies include canine VML models in addition to murine models, indicating cross-species conservation of immune–progenitor crosstalk with kinetic differences (larouche2023spatiotemporalmappingof pages 1-3).

15. Model Organisms

Commonly used experimental systems include: - Mouse models with standardized defect sizes (e.g., subcritical vs critical millimeter-scale injuries) enabling immune/omics comparisons (hymel2023identifyingdysregulatedimmune pages 1-2, chowdary2023macrophagemediatedpdgfactivation pages 1-3). - Rat tibialis anterior VML models used for minced muscle repair and cytokine delivery studies (huynh2023localil10delivery pages 1-2). - Canine models used in spatial transcriptomic analyses alongside mouse, supporting translational relevance (larouche2023spatiotemporalmappingof pages 1-3).

Key Quantitative Evidence Map (summary table)

The following table consolidates major quantitative thresholds, burden statistics, human clinical outcomes, and key mechanistic findings across the retrieved literature.

Topic Key data/claim Evidence type (human/animal/in vitro/trial protocol) Source (first author, year) PMID if known URL Citation context ID
Definition VML is the traumatic or surgical loss of skeletal muscle resulting in functional impairment. Human/clinical review Grogan, 2011 https://doi.org/10.5435/00124635-201102001-00007 (grogan2011volumetricmuscleloss pages 1-3)
Quantitative threshold Loss of skeletal muscle exceeding 20% is cited as a threshold beyond which innate repair/regeneration is permanently compromised. Review/synthesized clinical-preclinical Gahlawat, 2024 https://doi.org/10.1007/s10439-024-03541-w (gahlawat2024tissueengineered3d pages 1-3)
Alternative threshold VML has also been described as loss of over ~10% of muscle mass causing functional impairment. In vitro/review context Patel, 2019 https://doi.org/10.1088/1748-605x/ab0b06 (patel2019alignednanofibersof pages 1-5)
Trial enrollment definition Human VML trial protocol required both a structural deficit ≥20% of the muscle group mass and a functional deficit ≥25% versus the contralateral limb. Trial protocol Rubin/NCT04051242, 2020 https://clinicaltrials.gov/study/NCT04051242 (NCT04051242 chunk 2)
Epidemiology/burden VML is disproportionately common in military populations, comprising ~50% of combat-related injuries. Review Gahlawat, 2024 https://doi.org/10.1007/s10439-024-03541-w (gahlawat2024tissueengineered3d pages 1-3)
Extremity trauma burden Extremity wounds are the majority of soldier injuries in OEF/OIF, and >75% are due to explosions. Human clinical review Grogan, 2011 https://doi.org/10.5435/00124635-201102001-00007 (grogan2011volumetricmuscleloss pages 1-3)
Disability burden Severe extremity injuries such as type-III open tibia fractures with major soft-tissue loss are associated with a 65% incidence of permanent disability/medical retirement. Review Gahlawat, 2024 https://doi.org/10.1007/s10439-024-03541-w (gahlawat2024tissueengineered3d pages 1-3)
Human cohort outcomes In a 13-patient ECM bioscaffold cohort, mean improvement at 6 months was 37.3% in strength and 27.1% in range-of-motion versus pre-op. Human cohort Dziki, 2016 https://doi.org/10.1038/npjregenmed.2016.8 (dziki2016anacellularbiologic pages 1-2)
Human cohort baseline severity In the same 13-patient cohort, mean estimated tissue deficit was ~66.2% (individual deficits ~25% to 90%). Human cohort Dziki, 2016 https://doi.org/10.1038/npjregenmed.2016.8 (dziki2016anacellularbiologic pages 1-2)
Human evidence caveat Case reports of quadriceps acellular biomaterial repair showed minimal net recovery: 72%→~68% deficit at 4 months in one patient and 89%→~87% deficit at ~6 months in another. Human case reports/review Greising, 2019 https://doi.org/10.1089/ten.teb.2019.0207 (greising2019therapeuticapproachesfor pages 14-16)
Meta-analysis efficacy Across 44 animal studies, pooled functional benefit of VML treatments was Hedges’ g 0.75 (95% CI 0.53–0.96; p<0.0000001), corresponding to ~16% average beneficial effect. Animal systematic review/meta-analysis Greising, 2019 https://doi.org/10.1089/ten.teb.2019.0207 (greising2019therapeuticapproachesfor pages 1-3)
Best-performing treatment class Network meta-analysis suggested acellular biomaterial combined with stem/progenitor cells was the most effective experimental strategy. Animal systematic review/meta-analysis Greising, 2019 https://doi.org/10.1089/ten.teb.2019.0207 (greising2019therapeuticapproachesfor pages 1-3)
Critical vs subcritical injury In murine quadriceps, 2 mm defects regenerated while 3 mm defects produced persistent fibrotic scarring and chronic inflammation through 4 weeks. Animal primary study Hymel, 2023 https://doi.org/10.1038/s42003-023-04790-6 (hymel2023identifyingdysregulatedimmune pages 1-2)
Mechanism: immune dysregulation Critical VML showed sustained M2-like and CD206hiLy6Chi hybrid macrophages co-localized with FAPs in collagen-rich regions, implicating macrophage–FAP crosstalk in fibrosis. Animal primary study Hymel, 2023 https://doi.org/10.1038/s42003-023-04790-6 (hymel2023identifyingdysregulatedimmune pages 1-2)
Mechanism: spatial fibrosis program Spatial transcriptomics/scRNA-seq showed macrophages concentrated in the defect zone, MDCs/FAPs in defect/transition zones, and MuSCs largely restricted to transition zones; TGFBR2 inhibition improved MuSC infiltration and reduced fibrosis. Animal primary study/omics Larouche, 2023 https://doi.org/10.1101/2022.06.03.494707 (larouche2023spatiotemporalmappingof pages 1-3)
Mechanism: lipid mediators Degenerative VML showed increased pro-inflammatory eicosanoids (e.g., LTB4, PGE2, PGF2α) with insufficient rise in pro-resolving mediators (e.g., MaR1, PD1, RvD6). Animal primary study/metabolipidomics Castor-Macias, 2023 https://doi.org/10.7554/elife.86437 (castormacias2023maresin1repletion pages 9-11, castormacias2023maresin1repletion pages 2-5)
Immunotherapy result Delayed local IL-10 delivery after minced-muscle repair improved contractile torque to 82% of uninjured values and 170% of PBS controls at 56 days. Animal primary study Huynh, 2023 https://doi.org/10.1038/s41598-023-27981-x (huynh2023localil10delivery pages 1-2)
Pro-resolving mediator result Maresin 1 repletion reduced neutrophils/macrophages, attenuated fibrosis, increased MuSC activation, and partially restored force after degenerative VML. Animal primary study Castor-Macias, 2023 https://doi.org/10.7554/elife.86437 (castormacias2023maresin1repletion pages 9-11, castormacias2023maresin1repletion pages 1-2)
Standard of care Current clinical management includes physical therapy/orthotics and soft-tissue reconstruction such as functional free muscle transfer; these approaches have donor-site morbidity and limited restoration of function. Human clinical review Grogan, 2011 https://doi.org/10.5435/00124635-201102001-00007 (grogan2011volumetricmuscleloss pages 1-3)

Table: This table summarizes the most actionable quantitative definitions, burden statistics, human clinical results, and recent mechanistic findings for volumetric muscle loss. It is useful as a compact evidence map spanning disease characterization, translational thresholds, and therapeutic implications.

Visual Evidence (figures/tables)

A 2024 review provides schematic summaries of (i) VML pathophysiology (immune infiltration → impaired satellite cell migration → avascular fibrous scar) and (ii) tissue engineering strategies (in situ / in vivo / in vitro TE), plus tables of biomaterials and growth factors used in TE constructs (gahlawat2024tissueengineered3d media 816f8097, gahlawat2024tissueengineered3d media 4d3d8f7b, gahlawat2024tissueengineered3d media a8bea718, gahlawat2024tissueengineered3d media 26d381a5).

Notes on evidence limitations for knowledge-base population

  • Robust registry-style epidemiology (incidence/prevalence per 100,000) and standardized ICD/MeSH/MONDO identifiers were not available in retrieved sources using the tools in this run; the report therefore emphasizes well-supported operational definitions, burden statistics in military trauma, and translational thresholds used in trials and preclinical modeling.

References

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