Split Skin Grafting (Split-Thickness Skin Graft - STSG)

Definition

• Thin: 0.008-0.012 in (0.2-0.3 mm)
• Medium: 0.012-0.016 in (0.3-0.4 mm)
• Thick: 0.016-0.024 in (0.4-0.6 mm)

Historical Background

Wound Healing - Graft Take

Phase 1: Plasmatic Imbibition (first 24 hours)

• Fibrin glue attaches the graft to the recipient bed
• The graft absorbs wound exudate, becoming edematous (gaining up to 40% in weight)
• This hydration maintains graft vessel patency and nutrient supply until revascularization begins

Phase 2: Inosculation (48-72 hours)

• Anastomoses form between recipient bed vessels and pre-existing dermal vessels in the graft
• This process is called inosculation

Phase 3: Vascular Proliferation (days 3-7)

• Sprouting and budding of new vessels in both graft and bed
• Bridging phenomenon: vascular connections from vascularized areas carry nutrients across small avascular zones
• Full circulation is restored within 4-7 days

Phase 4: Remodeling

• Lymphatic restoration parallels blood supply recovery over the first week
• Epidermal proliferation occurs from days 4-8 and persists for weeks
• Sebaceous and eccrine glands may degenerate initially but can partially regenerate

Donor Sites

• Thigh (inner upper thigh preferred - covered area)
• Buttocks
• Scalp - safe, does not cause alopecia; regrowth hides scarring; in men, limited to occipital and temporal regions (not sensitive to androgenic alopecia)

Harvesting Technique

1. Measure the defect and mark the donor site
2. Coat skin with mineral oil; apply traction with gauze or towel clamp
3. Use an electric dermatome set at 0.2-0.3 mm (2-3 tenths of a mm), angled 45-60° to the skin
4. Apply even pressure across the blade width; advance in a smooth, controlled movement - no jerky movements
5. Correct harvest depth leaves light punctate bleeding (papillary dermis) with no visible fat lobules

• Excessive bleeding or visible fat = too deep (reticular dermis) - reduce thickness

1. After harvesting, achieve hemostasis with epinephrine-soaked gauze (1:10,000-20,000)
2. Local buprenorphine injections can reduce postoperative donor site pain

Meshing and Expansion

• Meshing (mesh graft device): Creates a net/lattice pattern; allows fluid to drain and surface area to expand
• Expansion ratios: 1:1.5, 1:2, 1:3, 1:6, 1:9
• At ratios ≥1:6, the net is too fragile for staples and requires protective allograft or xenograft coverage (Alexander technique)
• Meek device: Cuts graft into small square fragments glued onto folded gauze; expansion ratios 1:1.1 to 1:12

Applications / Indications

• Large wounds (burns, traumatic skin loss, chronic ulcers)
• Small defects of the oral cavity
• Maxillectomy defect internal lining
• Auricular defects (when intact perichondrium is present)
• Free flap donor site coverage
• Large scalp defects (when galea or periosteum are intact, or bleeding diploë is surgically exposed)
• Congenital aural atresia repair
• Orbital exenteration socket lining
• Prosthetic reconstruction defects

STSG vs FTSG Comparison

Recipient Bed Requirements

• Good vascularity (granulation tissue, periosteum, perichondrium, peritenon, perineurium)
• Absence of eschar or necrotic tissue
• Low bacterial load

Causes of Graft Failure

Donor Site Care

• The donor wound heals by re-epithelialization from residual dermal appendages (hair follicles, sweat glands left behind)
• Healing is fastest when the wound is kept moist - an occlusive semi-permeable dressing retains wound exudate in contact with the surface
• Thicker grafts taken = less dermis remains = slower donor site healing and more scarring

Advantages and Disadvantages

• Higher take rate than FTSG (less metabolic demand, tolerates lower vascularity)
• Donor site heals spontaneously without surgical closure
• Can cover large areas, especially when meshed
• Thinner grafts have the most reliable neovascularization

• Poor colour match, often hyperpigmented or hypopigmented
• Poor texture
• More secondary contraction than FTSG (functional and cosmetic problem)
• Less robust - susceptible to trauma
• Limited sensory recovery
• No hair growth (lacks follicles)
• Visible "mesh" pattern if meshed graft is used long-term

Systemic Factors Affecting Graft Take

• Diabetes mellitus
• Smoking (nicotine-induced vasoconstriction)
• Previous radiotherapy or chemotherapy
• Nutritional deficiency / hypoalbuminemia
• Immunosuppression
• Peripheral vascular disease

Split Skin Grafting (Split-Thickness Skin Graft - STSG)

Definition and Anatomy

Historical Background

Stages of Graft Healing ("Graft Take")

Revascularization - Three Processes

1. Inosculation - the cut ends of vessels in the recipient bed join directly to cut vessel ends within the graft
2. Revascularization - ingrowth of new vessels from the bed into the graft, creating new vascular channels
3. Neovascularization - degenerated endothelium of old cut vessels leaves behind basement membrane, which acts as a conduit for capillary bud growth

Donor Sites

• Inner upper thigh - most common
• Buttocks/gluteal region
• Scalp - safe, does not cause permanent alopecia (hair regrowth hides scarring); in men, limited to occipital and temporal regions not susceptible to androgenic alopecia

Harvesting Technique

1. Measure the defect; mark and prepare the donor site
2. Coat skin with mineral oil; apply traction with gauze or towel clamp
3. Use an electric dermatome set at 0.2-0.3 mm (2-3 tenths of a mm), angled 45-60° to the skin surface
4. Apply even pressure across the full blade width; use a smooth, controlled forward movement - jerks will interrupt the harvest
5. Correct harvest depth produces light punctate bleeding (papillary dermis) with no visible fat lobules

• Excessive bleeding or visible fat lobules = harvested too deep (reticular dermis) → reduce thickness setting

1. Achieve donor site hemostasis with epinephrine-soaked gauze (1:10,000-20,000)
2. Local buprenorphine injections can be given at the donor site to reduce postoperative pain

Graft Application

• Applied dermis-side down on the wound bed
• Fixed with staples, thrombin glue (wound bed spray), cyanoacrylate surgical glue (at skin-graft junction), or Prolene sutures (hands and face)
• Absorbable sutures should be avoided - they promote inflammatory granulomas
• Graft junctions should be placed perpendicular to biodynamic excisional skin tension lines while respecting aesthetic units, as junction areas are the most susceptible sites for hypertrophic scarring

Preventing Fluid Accumulation

• "Pie-crust" technique: Stab incisions made with a blade or needle to allow fluid egress and prevent haematoma/seroma (used in non-meshed or cosmetically sensitive areas)
• Meshing: Standard for large areas (see below)

Meshing and Expansion

Mesh Graft Device

• Creates a net/lattice pattern allowing fluid drainage and area expansion
• Expansion ratios: 1:1.5, 1:2, 1:3, 1:6, 1:9
• At ratios ≥1:6, the mesh is too fragile for staple fixation alone and must be protected by allograft or xenograft (Alexander technique)
• Long-term: the mesh/net pattern remains visible - inferior cosmetic result

Meek Device

• Cuts graft into multiple small square fragments, glued to folded gauze
• When gauze is unfolded, fragments are regularly spaced apart
• Expansion ratios: 1:1.1 to 1:12 (greater range than mesh device)

Alexander Technique

Indications / Applications

• Burns - the primary indication for large STSG and meshing
• Large traumatic skin defects
• Chronic wounds/ulcers
• Oral cavity defects (small)
• Maxillectomy cheek flap defects (internal lining)
• Auricular defects (when intact perichondrium is present)
• Free flap donor site coverage
• Large scalp defects (intact galea/periosteum, or bleeding diploë)
• Congenital aural atresia repair
• Orbital exenteration socket lining
• Prosthetic reconstruction defect lining

STSG vs FTSG - Key Comparison

Factors Affecting Graft Healing

Local (recipient bed) factors:

• Vascularity of the bed
• Presence of infection
• Haematoma or seroma under the graft
• Prior radiotherapy to the area

Systemic factors:

• Diabetes mellitus
• Smoking (nicotine-induced vasoconstriction)
• Previous chemotherapy or radiotherapy
• Malnutrition / hypoalbuminemia
• Immunosuppression
• Peripheral vascular disease

Causes of Graft Failure

Donor Site Care

• The donor wound heals by re-epithelialization from residual dermal appendages (hair follicles, sweat glands) retained in the dermis
• Healing is fastest when the wound is kept moist - an occlusive semi-permeable dressing retains exudate and promotes re-epithelialization
• Thicker graft harvested = fewer appendages remaining = slower donor site healing and increased scarring risk

Dermal Regenerative Templates (Combined Use with STSG)

• Biological: Integra, Matriderm, Nevelia
• Synthetic: BMT

• Mono-layer matrix: STSG applied immediately
• Bi-layer matrix: STSG applied after 3 weeks of maturation

Advantages and Disadvantages

• High take rate (tolerates lower vascularity than FTSG)
• Donor site heals spontaneously (no surgical closure needed)
• Can cover very large areas, especially when meshed
• Thinner grafts revascularize most reliably

• Poor colour match - abnormal pigmentation common
• Poor texture
• More secondary contraction (functional and cosmetic problems)
• Less durable, susceptible to trauma
• Limited sensory recovery
• No hair growth
• Visible mesh pattern with meshed grafts (long-term)

Types of Grafting

Classification 1 - By Source (Biological Relationship)

Classification 2 - By Tissue Type (Composition)

A. Skin Grafts

1. Split-Thickness Skin Graft (STSG)

• Contains: full epidermis + partial dermis
• Sub-types: thin (0.008-0.012 in), medium (0.012-0.016 in), thick (0.016-0.024 in)
• Donor site: heals spontaneously by re-epithelialization (hair follicles and sweat glands remain)
• Can cover large areas; can be meshed to expand further
• Undergoes more secondary contraction, poorer colour match, less robust

2. Full-Thickness Skin Graft (FTSG)

• Contains: full epidermis + full dermis (including all adnexal structures)
• Donor site: must be closed primarily (limited graft size)
• Better colour match, less secondary contraction, more robust
• Requires richer vascular bed for take
• Common donor sites: postauricular, preauricular, upper eyelid, supraclavicular, nasolabial

STSG vs FTSG Summary

B. Composite Grafts

• Contain two or more different tissue types in a single graft unit
• Examples:
• Chondrocutaneous graft (cartilage + skin) - from auricle; used for alar rim and small ear defects
• Septal mucosal graft (septal cartilage + mucosa) - used for eyelid reconstruction (provides structural support + mucosal lining)
• Osteocutaneous graft (bone + skin)
• Useful for reconstructing composite defects requiring multiple tissue layers simultaneously
• Survival depends on rapid revascularization from all surrounding margins; size is therefore limited

C. Bone Grafts

By Source:

• Autograft: Patient's own bone (gold standard). Common harvest sites: iliac crest, fibula, tibia
• Allograft: Cadaveric bone from a bone bank; comes as cancellous, cortical, or demineralized bone matrix (DBM)
• Vascularized bone graft: Transferred with its blood supply (e.g. free fibula flap) - most reliable for large defects

By Structure:

• Cancellous bone graft: Spongy, highly osteogenic; rapid incorporation; used for filling defects and promoting union
• Cortical bone graft: Dense, provides structural support; slower incorporation; used for bridging defects in long bones
• Demineralized bone matrix (DBM): Processed allograft; removes mineral content to expose osteoinductive proteins (BMPs); potent osteoinducer

Bone Graft Properties

• Osteogenesis: Graft contains viable cells that directly form new bone
• Osteoconduction: Graft provides a scaffold for host bone ingrowth
• Osteoinduction: Graft stimulates local mesenchymal cells to differentiate into osteoblasts (via BMPs)

D. Cartilage Grafts

• Transferred without blood supply (avascular tissue - survives by diffusion)
• Types:
• Septal cartilage: Nasal dorsal augmentation, tip support, spreader grafts, alar batten grafts; must leave 1-1.5 cm caudal and dorsal struts intact
• Auricular cartilage: Harvested from the conchal bowl with minimal cosmetic deficit; similar indications to septal cartilage
• Costal cartilage: 6th-8th ribs; used for nasal dorsal reconstruction (saddle nose), auricular reconstruction (microtia); requires balanced carving to prevent warping
• Free cartilage graft: Cartilage with its overlying perichondrium; perichondrium aids survival

E. Nerve Grafts

• A graft interposed between two cut nerve ends when primary tension-free repair is not possible
• Acts as a scaffold for axonal regrowth
• Gold standard donor: sural nerve (purely sensory - minimal functional deficit at donor site)
• Autologous nerve graft is preferred; allografts are also available
• The graft itself does not survive - it provides a conduit; Schwann cell tubes guide regenerating axons

F. Tendon Grafts

• Used when a tendon defect is too large for direct repair
• Graft placed through the intact tendon sheath (one-stage) or after sheath reconstruction using a silicone rod (two-stage Hunter technique)
• Common donor tendons: palmaris longus, plantaris, toe extensors
• The graft undergoes ligamentisation - gradual replacement by host tissue
• Also used for ligament reconstruction (e.g. ACL reconstruction using hamstring or patellar tendon graft)

G. Fat Grafts

• Transferred without blood supply; survives by imbibition then neovascularization
• Used for volume restoration, contour deformity correction, and facial rejuvenation
• High absorption/resorption rate is a limitation; over-correction is typically performed

H. Mucosal Grafts

• Full-thickness mucosal grafts (e.g. buccal mucosa, oral mucosa)
• Used in urethral reconstruction (hypospadias repair, urethral strictures), eyelid reconstruction
• Buccal mucosal graft is the most commonly used mucosal graft in urology

Graft vs Flap - The Reconstructive Ladder

1. Secondary intention healing
2. Primary closure
3. Skin graft (STSG → FTSG)
4. Local flap
5. Regional flap
6. Free tissue transfer (microvascular flap)

Morel-Lavallée Lesion

Definition

Mechanism of Injury

• Perforating arteries
• Perforating veins
• Lymphatic channels

Common Locations

• Thigh and lateral hip - most common (associated with pelvic fractures)
• Pelvis / buttock
• Knee
• Lumbar region
• Scapular region
• Arm / upper limb (less common but well described)
• Cervico-thoracic region (rare)

Clinical Presentation

• Soft fluctuant swelling over the affected area
• Hypermobility of the overlying skin - skin slides freely over the deeper tissues
• Fluid wave palpable in the subcutaneous tissue
• Skin may appear bruised, ecchymotic, or have a violaceous discolouration
• In early stages the lesion may be subtle and easily missed - particularly in obese patients
• In large or chronic lesions: skin may become non-viable, showing fixed staining and thrombosis of subcutaneous veins

Associations

• High-velocity trauma (road traffic collisions, crush injuries)
• Pelvic fractures (especially those with shear component)
• Acetabular fractures
• Obesity - increases risk and size of lesion
• Operating through an active MLL significantly increases postoperative infection rate (up to 12%)

Diagnosis

Clinical

• High index of suspicion in any patient with appropriate mechanism plus skin hypermobility or subcutaneous fluid wave
• May initially be missed on trauma survey

Imaging

Classification

1. Limited degloving with abrasion or avulsion
2. Non-circumferential degloving
3. Circumferential single plane degloving
4. Circumferential multiplanar degloving

Management

Conservative / Non-operative

• Observation with compression bandaging for small, stable lesions
• Risk of recurrence is high with conservative management alone
• Simple aspiration is usually ineffective (high recurrence rate)

Percutaneous Drainage (Tseng-Tornetta Technique)

1. Position patient to expose the lesion
2. Make a 2-cm incision over the distal aspect of the lesion
3. Make a second 2-cm incision at the superior and posterior extent
4. Determine extent using a suction tip passed through the cavity
5. Additional incisions as needed depending on lesion extent
6. Send fluid for culture and sensitivity
7. Drain haematoma with suction
8. Use a plastic brush (canal preparation brush from joint replacement) to debride loose fat
9. Pulsed lavage irrigation until fluid runs clear and no fat debris remains
10. Place medium closed suction drain to drain the entire cavity
11. Close incisions tightly
12. Attach drain to wall suction until drainage <30 mL/24 hours (may require up to 8 days)
13. Continue IV cephalosporin for 24 hours after drain removal

Open Surgical Debridement

• For large lesions (>50 mL), infected collections, or failed percutaneous drainage
• Collections >50 mL may be best treated surgically rather than with aspiration alone
• Involves open debridement of the pseudocyst wall, removal of necrotic fat and fibrous capsule
• Wound closure with suction drains or closure over negative pressure wound therapy (NPWT)
• If skin is non-viable: serial debridement until punctate dermal bleeding seen from viable tissue, followed by split-skin grafting or flap coverage

In the Context of Fractures (e.g. Pelvic/Acetabular)

• MLL over the planned surgical field is a relative contraindication to immediate open fixation due to high infection risk
• Preferred strategy: percutaneous decompression and debridement first, then delayed ORIF at least 24 hours after drain removal and output <30 mL/day
• Some acetabular fractures can be treated via an anterior approach to completely avoid the lateral MLL
• Operating through an active MLL is associated with infection rates up to 12%

Complications

Key Points Summary

• MLL = closed degloving from tangential shear force → haemolymphatic collection between subcutaneous fat and deep fascia
• Frequently missed - requires active clinical suspicion
• Hypermobile skin and fluid wave are the key clinical signs
• MRI is the gold standard for diagnosis and characterisation; ultrasound is useful at bedside
• Associated with pelvic fractures, especially in obese patients; also occurs in the upper limb (including the arm)
• Treatment: observation/compression (small), percutaneous drainage with lavage (moderate, <3 days), open debridement (large, infected, failed)
• In fracture surgery: drain before operating to avoid catastrophic infection
• Culture collections even when "closed" - up to 46% are positive