Skin Grafts and Flaps

Skin Grafts and Flaps

1. Skin Grafts
• segment of skin and dermis that is transplanted to another recipient site on the body
• derive their blood supply from recipient site revascularization


1. Classification
• autograft: from self
• allograft: from a nongenetically similar donor
• heterograft (or xenograft): from another species, often a pig
• split-thickness grafts (STSG) contain the epidermis and a portion of the dermis
• full-thickness grafts (FTSG) contain the epidermis and the entire dermis


1. STSG
• harvested with a dermatome that can be adjusted for width and thickness
• thicknesses range from 0.006 to 0.024 inches
• the thinner the graft, the more reliable is its take, but its cosmetic result and durability are worse
• meshed grafts, usually in a 1:1.5 or 1:2 ratio, allow for greater coverage and minimal fluid accumulation under the graft; however, they have a poor cosmetic appearance and a higher rate of contraction
• donor sites may be reused once they have reepithelialized
• disadvantages of STSGs include contracture over time, abnormal pigmentation and texture, and poor durability if subject to trauma


2. FTSG
• removed with a knife
• donor site must be closed primarily
• the subcutaneous fat must be removed from the deep portion of the graft
• can only be used for small defects, usually on the face and hands
• contains skin appendages, so they can grow hair and secrete sebum to lubricate the skin
• more durable and cosmetically acceptable than STSGs
• graft take is not as predictable because more tissue must be revascularized from the recipient bed


2. Graft Take
• survival of the skin graft requires a vascularized wound recipient bed
• wound bed must be free of infection and debris
• graftable beds include healthy soft tissues, periosteum, perichondrium, peritenon
• poor graft beds include exposed bone, cartilage, tendon, and chronic fibrotic granulation tissue
• graft take occurs in several phases:


1. Serum Imbibition
• fibrin layer forms at the graft-bed interface, which holds the graft in place
• during the first 48 hours, the graft survives on plasma exudate from the host bed capillaries


2. Inosculation
• occurs after 48 hours
• new capillaries begin to develop within the fibrin layer


3. Revascularization
• blood vessels grow from the wound bed into the graft
• revascularization is complete by 4 - 5 days after graft placement


4. Organization
• by postgraft day 7, fibroblasts replace the fibrin layer
• grafts are securely fixed to the bed by postgraft day 10 – 14
• reinnervation of the graft begins at 4 to 5 weeks, and is complete by 12 – 24 months
• pain returns first, with light touch and temperature returning later


3. Graft Failure
• anything that precludes the graft from adhering to the wound bed will result in graft failure, since revascularization will not occur
• fluid accumulation under the graft, primarily from hematoma formation, is the most common cause of graft failure
• shearing or movement of the graft on the bed will also prevent revascularization
• other reasons for graft failure include infection, poor quality wound bed, and thickness of the graft


1. Dressings
• can prevent some impediments to graft take
• a bolster or tie-over dressing left in place for 4 – 5 days can prevent hematoma or seroma accumulation, as well as minimize movement of the graft on the bed
• wound VACs can be placed over a graft to stabilize it in place and to evacuate fluid
• wound VACs are especially useful for large wounds or wounds on a complicated three-dimensional surface
• grafts near or over a joint may require a splint or cast to prevent movement of the graft


2. Local Skin Flaps
• rely on the inherent elasticity of the skin and are most useful in older patients with looser skin
• blood supply is based on the tiny vessels in the dermal-subdermal plexus
• usually match the skin at the recipient site in color, texture, hair, and thickness
• donor site can usually be primarily closed, although occasionally a skin graft is necessary
• failure of a skin flap usually results in necrosis of the most distal portion of the transferred tissue
• failure of a flap is usually due to poor flap design, in which the size of the flap exceeds its vascular supply – a reliable length-to-width ratio is 3:1
• other reasons for flap failure include mechanical compression from a hematoma, compressive dressing, or kinking of the flap


1. Rotation Flaps
• semicircular flaps that revolve in an arc around a pivot point to shift tissue in a circle
• defect to be closed is often converted into a triangular shape



2. Transposition Flaps
• rectangular or square
• turn laterally to reach the defect
• secondary defect may require a STSG to close



3. Advancement Flaps
• move directly forward
• rely on skin elasticity to stretch and fill the defect
• useful for forehead and scalp defects



4. V-Y Advancement Flaps
• advance skin on each side of a V-shaped incision to close the wound with a Y-shaped closure
• useful for closing fingertip defects



5. Rhomboid Flaps
• rely on the looseness of adjacent skin to transfer a rhomboid-shaped flap into a defect that has been converted into a similar rhomboid shape



6. Z-Plasty
• transposes two triangular flaps, each into the donor site of the other, to achieve central limb lengthening
• used to improve the functional and cosmetic appearance of scars
• used in burn surgery to release linear burn scar contractures



3. Muscle Flaps
• may be used as pure muscle flaps or as myocutaneous flaps


1. Anatomy
• individual muscles have been classed into 5 types based on their blood supply
• muscles may have a singular vascular pedicle (tensor fascia lata, gastrocnemius), a dominant pedicle and a minor pedicle (gracilis, trapezius); two dominant pedicles (gluteus maximus); segmental pedicles (sartorius, tibialis anterior); and a dominant vessel with secondary segmental pedicles (latissimus dorsi)



2. Clinical Uses
• since muscle flaps have an excellent blood supply, they are more useful than skin flaps in irradiated or infected wounds
• transverse rectus abdominis myocutaneous (TRAM) and latissimus dorsi flaps are commonly used in breast reconstruction to provide bulk
• gracilis flaps are used to facilitate healing in irradiated perineal wounds following abdominoperineal resections
• a major consideration with muscle flaps is whether the loss of function is acceptable


4. Fasciocutaneous Flaps
• skin flaps that contain the deep fascia


1. Anatomy
• vascular pedicles run between muscles in the intermuscular septum
• these vessels enter the deep fascia and form a fascial plexus
• the fascial plexus is made up of multiple intercommunicating vessels
• since blood flow is multidirectional, fasciocutaneous flaps can be distally based


2. Clinical Uses
• the length of a skin flap can be increased if it is oriented along the long axis of an extremity and if the deep fascia is included
• since the flap can be distally based, it can be used to cover a defect located at the end of an extremity
• one example is the distal-based sural flap, which is used to cover the foot and ankle
• unclear whether these flaps are as effective as muscle flaps in infected and irradiated wounds
• a clear advantage of fasciocutaneous flaps is that no functioning muscle is sacrificed







5. Perforator Flaps
• does not require sacrificing functional muscle or fascia
• the musculocutaneous or fasciocutaneous perforator vessels must be carefully dissected out and preserved
• because of their small size and anatomic variability, Doppler ultrasound must be used to locate the vessels
• deep inferior epigastric artery (DIEP) perforator flaps are used in breast reconstruction



6. Free Flaps
• distant tissue with a pedicled arterial and venous supply is anastomosed to vessels at the recipient site to reestablish flow
• requires specialized training in microsurgery and microvascular anastomoses
• thrombosis of the arterial anastomosis in the first 48 hours is the most common reason for graft failure, but salvage rates are high with prompt reexploration
• postoperative anticoagulation has not been shown to increase graft survival rates