Grafts: Skin, Bone, and Fat 
Skin Grafts
Anatomy
Stages of graft survival:

• Imbibition – the graft passively absorbs nutrients from the wound bed (initially)
• Inosculation – existing vessels/capillaries start to come together to supply the graft
• Neovascularization – new blood vessels grow into graft (2-3 days)

Contraction

• primary contraction occurs immediately after harvest and is due to the recoil of elastic fibers in the dermis
• Secondary contraction is due to myofibroblasts after the wound heals
• Least amount of secondary contracture: FTSG 
• Most amount: Healing by secondary intention 

Types of skin grafts
Full thickness skin grafts

• Harvest of the epidermis and dermis (so what’s left is subcu fat). Donor site must be closed
• Best for face and small defects as well as volar hand
• Less contracture in the long run, better texture once healed

Split thickness skin grafts

• Harvest epidermis and partial dermis via dermatome (0.8-1.4 1/1000 inch), leave behind adnexal remnants in the donor dermis so donor site can regrow (adnexal components house the regenerative cells).
• Less metabolic demand on recipient wound bed therefore higher graft take 
• Best for larger defects, and dorsal hand
• Undergo more contracture in the long run
• Meshing is an option to provide more surface area (decrease the donor site burden), better drainage, less infection, and better take, but will heal to a cobblestoned appearance
• Regenerated skin (ie skin grafts) have many characteristics of normal skin (capillary loops, retentions ridges, elastic and collagen fibers) but DO NOT have dermal appendages of hair follicles or sweat glands
• At the graft donor site – hair follicles contain the multipotent stem cells that allow for re-epithelialization o fthe donor site 
• Donor site healing
• moist occlusive dressing have less pain during the entire healing process (alginate > moist gauze/xeroform)

Biologic dressings 

• Bilayered skin substitute (apligraf, orcel in UK; integra in US)
• release matrix proteins encourage neodermis formation
• Results in improved cosmesis, diminished scar contracture or development of hypertrophic scar, increased elasticity 
• after 3-4 weeks, remove the top silicone layer and your neodermis is ready to receive a skin graft
• wound vac bolster of biologic dressing increases matrix take and decreases timing to skin graft

Fat grafts
Survival rate: 60% (about 1/3 dies)
Administration

• Inject in small aliquots and in a lattice shape
• graft soon after harvest (adipocytes start to die at room temperature and are almost completely dead at 4h)
• inject with a low shear device

Bone grafting
Anatomy
Bone Sources

• Cancellous bone has more osteoblasts and osteocytes so is better for osteogenic potential
• Cortical bone is dense so it offers higher stability and absorbs slower

• Common bone donor sites
• ribs 5-7 – split rib is good because the cancellous bone is more rapidly revascularized
• gerdy’s tubercle of the tibia (corticle window proximal and medial to tibialis anterior)
• iliac crest
• Cartilage – risk is warping (especially with an intact perichondrial layer)
• rib 11

• Autologous bone grafts are preferred for cranioplasty in children because they osseointegrate and grow with the child
• particulate graft can be harvested at any age
• split calvarial graft can be harvested starting around 5 years of age
• donor sites will reossify

Fracture Healing – 

• inflammation 0-3 days 
• Repair 1d-3wk (cartilaginous callus 3-6wk, bony union 4-8wk) 
• endochondral ossification (where cartilaginous soft callus becomes bony)
• Remodeling takes months to years

Graft regrowth
Osteoinduction 

• Induction of growth factors in surrounding host cells to become osteoblasts and create bone 
• BMP, cancellous bone graft, demineralized bone matrix

OsteoConduction 

• Replacement of graft by creeping, direct chemical bonding of alloplast to bony surface – alloplast acts as a scaffold and is eventually resorbed and replaced with new bone
• neovascularization at 6-8wk, full strength at 6-12mo
• Cortical bone grafts, Calcium hydroxyapatite

Osteogenesis

• autograft, vascularized bone transfer
• new bone formation from within the graft material