Pertinent Insights On Muscle Flaps
Frequently, local random flaps are less ideal than muscle flaps due to limited mobility of adjacent tissue for larger defects located at difficult surfaces of the foot and ankle. Muscle flaps can provide local blood supply to devascularized bone. Not only do these flaps enhance the delivery of antibiotics, they also provide a healthy surface for skin grafting. Muscle flaps have a dominant vascular pedicle that supplies the named muscle and the overlying skin secondary to perforating branches. While muscle flaps are classified based on five different vascular patterns overall, all flaps within the foot are classified as type II intrinsic muscles due to the presence of one dominant vessel at its origin and several minor vessels entering distally.16
The most widely used intrinsic muscle flaps for soft tissue reconstruction are the abductor hallucis, extensor digitorum brevis, flexor digitorum brevis and abductor digiti minimi. The abductor hallucis flap is preferred for plantar and medial wounds, such as those involving the first and central metatarsals, and one may also use these in conjunction with Charcot midfoot reconstructions.16 Surgeons may employ the extensor digitorum brevis flap for small ankle defects, the lateral calcaneus and lower tibial wounds. It is a relatively small muscle and the donor site carries a risk of non-healing due to sacrificing of perforators to this area during harvesting.
The flexor digitorum brevis flap is favored for plantar central wounds. Use of this flap often allows one to use primary closure for the donor site.8 Surgeons can utilize the abductor digiti minimi flap for tissue loss about the lateral aspect of the mid- and rearfoot. Surgeons often use this flap to close plantar lateral ulcerations.
In a retrospective study of 32 muscle flaps, Attinger and colleagues demonstrated that the presence of diabetes does not adversely affect the success of flap take. Therefore, one should consider muscle flaps for closure of small diabetic foot and ankle wounds with exposed tendon, joint and/or bone.17
Assessing The Viability Of Pedicle Flaps
A pedicle flap is a partially detached segment of skin and subcutaneous tissue. The flap’s circulation based viability is maintained by its base and the subsequent subdermal plexus. The main advantages of these flaps are a well defined surface, which is independent of a length to width ratio, and the preservation of the main vascular axis.
One should not use these flaps in areas with movement or variable tension. A flap with a direct cutaneous artery included has a better chance of survival than flaps without that direct cutaneous artery. Increasing the length of the flap or failing to include sufficient vascularity to the flap will increase the chance of dehiscence. When it comes to further divisions into fasciocutaneous, adipofascial or musculocutaneous types, one can dissect these depending on the particular need.
Common examples for reconstruction in the diabetic foot include the great toe fibular flap, medial plantar artery flap and reverse flow sural artery neurofasciocutaneous flap. The great toe fibular flap is useful when covering the plantar distal forefoot. It involves harvesting a large portion of full-thickness skin from the lateral aspect and incorporating the underlying pedicle, adipofascial and/or periosteum structures.18 Typically, one would close the donor site primarily or subsequently with a STSG or bioengineered skin substitute tissue.