OPBSPathologyMusculoskeletal
Must Know
- Epidermis is keratinised stratified squamous epithelium, avascular and fed by diffusion from capillaries below the basal lamina.
- Skin is a water-impermeable barrier against abrasion and microbes.
- Muscle fibres sit in endomysium, fascicles in perimysium and whole muscles in epimysium.
- Muscle cells cannot divide. Satellite cells give muscle its regenerative capacity.
- Most traumatic soft-tissue wounds heal by scar, sometimes with contracture.
- Healing runs on a spectrum from scarless regeneration through normal scar to hypertrophic scar and keloid.
- Fetal skin heals without scar up to about 24 weeks.
- Keloid appears to carry a genetic predisposition. Hypertrophic scar follows burns.
Phases of Wound Healing
| Phase | Duration | Dominant cells | Events |
|---|---|---|---|
| Inflammation | 48 to 72 hours | Platelets, neutrophils, then macrophages | Haematoma, mediator release, phagocytosis |
| Proliferation | At least 2 to 3 weeks | Fibroblasts, endothelial cells | Granulation tissue, angiogenesis, contraction, epithelialisation |
| Remodelling | Months | Fibroblasts, many cells apoptose | Type III collagen replaced by type I |
- Platelets release PDGF and IL-8. Mast cells raise blood flow and permeability.
- Neutrophils amplify inflammation with IL-1, IL-6 and TNF-α.
- Macrophages dominate late inflammation and drive the switch to proliferation.
- PDGF is the main stimulus for fibroblast migration.
- Myofibroblasts express smooth muscle actin, via MRTF-A, and contract the wound.
- Fibroblasts secrete MMPs to clear a path for migration and vessel ingrowth.
- Angiogenesis is driven by VEGF, FGF, angiopoietin, TGF-β, hypoxia and lactic acid.
- Fibroblast Neu differentiation factor drives keratinocyte migration from wound edges and hair follicles.
More on mediators
- TGF-β and MCP-1 attract monocytes and drive their maturation into macrophages.
- Macrophages release PDGF, VEGF, FGF, NGF, TGF-β, CTGF and Cyr-61 to build granulation tissue.
- T lymphocytes, fibrocytes and eosinophils also take part in inflammation.
- Fibroblasts migrate along fibrin, fibronectin, vitronectin and hyaluronic acid through integrin binding.
- Endothelial cells break down their own basement membrane to form new tubules.
Scar Versus Normal Skin
| Feature | Normal skin | Mature scar |
|---|---|---|
| Collagen arrangement | Basketweave | Parallel bundles |
| Collagen type | Not stated | 80 to 90 percent type I, rest type III |
| Tensile strength | Full | About 70 percent |
| Appendages and rete pegs | Present | Absent |
| Elastin | Normal | Reduced |
- Early scar is disorganised type III collagen.
- Scar never regains the full strength or flexibility of the original tissue.
Injury Patterns
- Fracture blisters form at the dermoepidermal junction from shear, often on the foot, ankle, leg, wrist and forearm.
- Haemorrhagic blisters signal deeper injury and scar more than serous blisters.
- Both blister types raise the risk of skin breakdown and infection.
- Morel-Lavallée lesion is shear separation of hypodermis from deep fascia, filling with blood, lymph and necrotic fat.
- The collection enlarges with time and forms a pseudocapsule.
- Up to almost 50 percent of Morel-Lavallée lesions are culture positive on aspiration.
- Aspirated or débrided lesions carry higher infection risk and recur often.
- Ballistic damage extends beyond the tract, worse with higher velocity, larger or deforming bullets and close range.
| Mellado and Bencardino type | Morel-Lavallée appearance |
|---|---|
| 1 | Simple seroma |
| 2 | Subacute haematoma |
| 3 | Mature organised haematoma |
| 4 | Closed fatty laceration with perifascial dissection |
| 5 | Perifascial nodular lesion |
| 6 | Infected, with sinus, septations and capsule |
Open Fracture Classification
- Gustilo and Anderson is the most used but has poor interobserver reliability.
- OTA Open Fracture Classification grades skin, muscle, bone, arterial injury and contamination, with better reliability.
- OTA OFC helps predict repeat débridement, NPWT or bead use and amputation.
Host Factors
- Low albumin and prealbumin prolong healing and raise infection.
- Poor oxygen delivery from vascular disease, diabetes, smoking or lung disease delays healing.
- Exogenous steroids impair scar formation and infection resistance.
- Healing capacity falls with age and with sun or therapeutic radiation.
- A wound is infected once pathogen load provokes a meaningful immune response. Below that it is colonised.
- Necrotic tissue cannot receive immune cells or systemic antibiotics, so needs débridement.
- Infected wounds should not be closed.
Interventions
- Donati-Allgöwer vertical mattress suture best preserves skin edge perfusion.
- No consensus exists on drain use.
- NPWT uses open cell foam at 75 to 125 mmHg, continuous or intermittent.
- NPWT shifts cytokines to an anti-inflammatory profile. TNF falls while VEGF, FGF-2, TGF-β and PDGF rise.
- Chronic wounds show raised cytokines and a prolonged, hyperactive neutrophil response.
- A moist occlusive environment speeds epithelialisation, by up to 40 percent in skin grafts.
- Bilayer collagen and silastic constructs can grow granulation over small areas of exposed tendon or bone.
| Morykwas pig work at 125 mmHg | Effect |
|---|---|
| Blood flow | Fourfold rise |
| Granulation tissue | 63 percent more continuous, 103 percent more intermittent |
| Bacterial clearance | Better by day 4 |
| Random flap survival | Up 21 percent |
| Antiseptic | Point to remember |
|---|---|
| Dakin solution | Buffered sodium hypochlorite, from World War I |
| Povidone-iodine | Fibroblast growth slowed at 0.01 percent, stopped at 0.1 percent |
| Hydrogen peroxide | 0.5 percent delayed early healing in rats, no difference by day 8 to 10 |
More on wound adjuncts
- Dakin solution at 0.00025 percent controlled four mould species with limited cytotoxicity in vitro.
- NPWT reduced wound complications in pilon, calcaneus and bicondylar plateau fractures.
- In NPWT, IL-1β fell only in acute wounds.
- Early flap cover of exposed tendon or bone adds vascularity and lowers infection risk.
- Morel-Lavallée lesions left alone may persist for months or years and leave thinned skin.
Exam Traps
- Scar collagen lies in parallel bundles. Normal skin collagen is basketweave.
- Early scar is type III collagen, mature scar is mostly type I.
- Gustilo and Anderson is common yet less reliable than OTA OFC.
- Intermittent NPWT produced more granulation than continuous.
Related pages. Debridement of Open Fractures, Surgical Site Infection, Union / Non-union
Source
Evans AR, Hayda RA. Contemporary Concepts in Soft-Tissue Wound Management. In. Aaron RK, editor. Orthopaedic Basic Science. Foundations of Clinical Practice. 5th ed. Philadelphia, Wolters Kluwer, 2021.
Practise Type X questions on this topic
Reviewed by Professor Phong Tran, Head of Orthopaedic Surgery, Western Health. Last updated 17 October 2026.