Skin Grafting (STSG & FTSG)

Skin grafting is the transfer of skin from a donor site to a recipient wound that cannot be closed primarily. Two principal variants are used in general surgery. A split-thickness skin graft (STSG) contains the epidermis plus a portion of the dermis (thin 0.005–0.012 inches, intermediate 0.012–0.018 inches, thick 0.018–0.030 inches); the donor site heals by re-epithelialization from residual epidermal appendages. A full-thickness skin graft (FTSG) contains the epidermis and the entire dermis; the donor site must be closed primarily (or itself grafted), so FTSGs are limited in size.

Indications for STSG include burn coverage after escharotomy/excision, traumatic wounds with adequate vascularized bed, postoperative wounds that cannot be closed (fasciotomy beds, large oncologic resections, chronic ulcers after debridement), and meshed coverage of large open wounds with limited donor sites. Indications for FTSG include facial and hand defects where contraction must be minimized, defects over joints, periorbital and ear reconstruction, and any wound where superior cosmesis is required.

Critical recipient bed requirements are vascularity and absence of infection. Grafts will not 'take' on bare bone without periosteum, bare tendon without paratenon, or bare cartilage without perichondrium, because these surfaces have inadequate microvascular supply. Active infection (>10⁵ organisms per gram of tissue, or any beta-hemolytic Streptococcus) must be cleared before grafting; the wound bed should appear clean and beefy red. Grafts placed on irradiated tissue, anticoagulated patients, or tobacco smokers have higher failure rates.

STSG donor sites are chosen for accessibility, surface area, and cosmesis of the residual scar. The anterolateral thigh is the most common donor site for adults — broad, flat, easily prepped, and produces an acceptable scar. The buttock is preferred for pediatric patients (the scar is concealed by clothing) and when large area is needed. The scalp (for facial reconstruction), the back, and the upper arm are alternatives.

FTSG donor sites are selected for color and texture match to the recipient site and for the ability to close the donor site primarily. Common FTSG donors include the postauricular and preauricular skin (for facial defects), the supraclavicular area, the upper eyelid, the groin crease (for hand defects — large area, hairless), and the volar forearm.

For STSG, the dermatome (electric or air-driven; Padgett, Zimmer, or Brown dermatomes are standard) is calibrated to the chosen thickness (typically 0.012–0.018 inches for general-surgery wounds). The donor site is shaved, prepped, and lubricated with mineral oil to allow smooth blade glide. The dermatome is held at 30–45° to the skin with firm downward and forward pressure; an assistant applies countertraction. The harvested graft is placed dermis-down on saline-soaked gauze.

If wider coverage is needed, the graft is meshed (1:1.5 or 1:3 expansion ratio) on a meshing skin board, which both expands surface area and allows drainage of seroma/hematoma through the interstices. The graft is placed on the recipient bed, oriented appropriately, trimmed to fit, and fixed in place with absorbable sutures, staples, or fibrin glue. A bolster dressing (mineral-oil-soaked cotton, Xeroform, or a foam-and-vacuum-assisted closure dressing) is sewn over the graft to maintain firm contact between graft and bed for 5–7 days. The donor site is dressed with a semi-occlusive dressing (Tegaderm, Mepilex, or fine mesh gauze) that allows re-epithelialization over 10–14 days.

For FTSG, the graft is harvested as an ellipse sized to the defect. The dermis is defatted carefully with scissors (subdermal fat impedes graft take). The donor site is closed primarily with interrupted sutures. The graft is inset into the recipient defect, secured with peripheral sutures, and bolstered as for an STSG.

Graft survival depends on three sequential phases. (1) Plasmatic imbibition occurs in the first 24–48 hours: the graft is avascular and absorbs nutrient-rich serum directly from the wound bed by capillary action, sustaining graft cells. (2) Inosculation begins at 48–72 hours: vessels in the wound bed and graft align and connect end-to-end, restoring rudimentary circulation. (3) Neovascularization occurs from days 4–7: new capillaries grow into the graft from the recipient bed, providing definitive perfusion. The graft is firmly adherent by 5–7 days; oily-yellow color signifies plasmatic imbibition, then pink mottling appears as inosculation progresses, then uniform pink color confirms neovascularization.

Any process that disrupts these phases causes graft failure. Hematoma or seroma physically separates the graft from the bed, preventing imbibition. Shear forces disrupt the fragile early vascular connections of inosculation. Infection digests the developing capillary network. Inadequate bed vascularity (the bare-bone/tendon/cartilage rule) provides no source for inosculation. The bolster dressing addresses the first two failure modes by maintaining apposition; meshing addresses fluid accumulation; preoperative bed debridement and culture-guided antibiotics address infection.

The bolster is left undisturbed for 5–7 days. At the first dressing change, the graft is inspected for take (pink color, intact, adherent to bed) versus failure (gray, fluid beneath, separation). Areas of partial loss are debrided and either re-grafted or allowed to heal by secondary intention. The donor site is kept clean and is allowed to re-epithelialize under a semi-occlusive dressing; it is typically healed by 10–14 days but may remain hypersensitive and discolored for months.

Reported take rates for STSG are 70–90% in clean wounds; rates are lower in chronic or compromised wounds. Long-term outcomes differ between graft types. STSGs contract substantially (up to 50% area loss over months), have less elastic skin, and are more prone to hyperpigmentation. FTSGs contract minimally, retain more normal skin texture and elasticity, and provide superior cosmesis at the cost of limited donor-site size.

Graft failure (partial or complete) is the most common adverse outcome. The four classic causes — hematoma, seroma, shear, and infection — should be screened for and corrected at first dressing change. Donor site complications include delayed healing (especially in older patients or with tobacco use), conversion to a full-thickness wound, scarring, hyperpigmentation, and rarely infection. Late complications include contracture (especially across joints, where contractile STSGs can produce flexion deformity — splinting and physical therapy are essential), keloid formation, and color mismatch in cosmetically visible sites.

On the oral boards, examiners commonly test: the histologic and functional differences between STSG and FTSG; the donor site options for each; the recipient bed vascularity rule (no graft on bare bone, tendon, or cartilage without their respective coverings); the three phases of graft take (imbibition → inosculation → neovascularization) and their timing; the four causes of graft failure (hematoma, seroma, shear, infection) with management of each; and the rationale for meshing and bolstering.