These authors discuss the use of the distally-based, extended extensor digitorum brevis muscle flap for limb salvage in a patient with diabetes and osteomyelitis of the great toe.
The extensor digitorum brevis muscle flap has been an option for local soft tissue reconstruction since the 1970s.1 Since that time, there has been an increased utilization of the muscle flap for a variety of applications including coverage of foot and ankle defects.2-12
Of particular interest is the extended, distally based extensor digitorum brevis muscle flap for salvage of the hallux.7,13,14 Since the hallux is vital in maintaining normal foot function, it would be ideal to preserve the hallux. Treatment becomes difficult when there is a significant post-surgical tissue defect along the operated hallux that is not amenable to skin grafting.
Reconstruction of the distal foot, especially the toe, has posed a particularly challenging problem. There are few local options available for the distal forefoot and toes such as the fillet of toe, the dorsometatarsal first web flap, and the distally-based dorsalis pedis flap. However, these options have significant donor site morbidity and a limited arc of rotation.
The proximity and advantages of the extensor digitorum brevis muscle makes it an option for coverage of the toes. The flap is useful due to the muscle’s size and thinness, consistent vascular anatomy, large vessel size, ease of dissection, minor donor site morbidity, arc of rotation and length of the pedicle. The limited bulk of the muscle allows for primary closure of the donor site. Since the muscle is a secondary toe extensor, it is expendable without a functional deficit. In terms of a reverse flow, the increased arc of rotation and length of the pedicle permits coverage of defects of the toes. Muscle flaps are preferred in the management of complicated wounds involving osteomyelitis. These flaps are pliable, contour to defects, fill dead space, provide improved tissue ingrowth, enhance the local delivery of antibiotics and revascularize underlying bone.
A Closer Look At The Relevant Anatomy
The extensor digitorum brevis muscle is a thin muscle located on the dorsum of the foot. It originates from the sinus tarsi and the dorsolateral surface of the calcaneus. It courses distally and medially, finally terminating on the base of the hallux and along the lateral aspect of extensor digitorum longus tendons of the second through fourth digits. The muscle shape is trapezoidal and its dimensions are typically 5 cm x 6 cm with a surface area of 19 to 34 cm2.4
The dorsalis pedis artery is a continuation of the anterior tibial artery, which courses inferior to the extensor retinaculum. The medial and lateral tarsal arteries branch from the dorsalis pedis artery.3 The medial tarsal artery travels medially and deep to the abductor hallucis muscle to connect with the medial plantar artery. The lateral tarsal artery runs laterally and situates itself along the deep surface of the extensor digitorum brevis muscle, serving as the muscle’s main supplier when present.
Anatomical variations exist in which additional muscular branches stem from the dorsalis pedis artery to the extensor digitorum brevis muscle. In some individuals, the perforating branch of the peroneal artery supplies the extensor digitorum brevis muscle. Once the dorsalis pedis artery reaches the first intermetatarsal space, it branches off deeply plantar and continues on as the first dorsal metatarsal artery. The first dorsal metatarsal artery then courses distally towards the first web space where it passes over the deep transverse intermetatarsal ligament, branches into two dorsal digital arteries, and communicates with the plantar arterial network.
The extensor digitorum brevis muscle has a type 2 vascular pattern, which means its dominant vascular pedicle is near the muscle origin and has minor vascular pedicles. Typically, the lateral tarsal artery or the dorsalis pedis supplies the dominant vascular pedicle.
There are three ways to provide blood supply for a distally based flap: the medial tarsal artery; the connection between the first dorsal interosseous artery and the plantar system at the level of the metatarsal head; and the deep plantar branch with communication of the lateral plantar artery. The most reliable option is at the pivot point at the tarsometatarsal joint since it has the most reliable vasculature and venous return. The extended, distally-based extensor digitorum brevis muscle flap is based on the first dorsal metatarsal artery.
One should confirm the presence of retrograde flow using a Doppler and/or angiogram before committing to this procedure. If the dominant vascularity is based on the peroneal or dorsalis pedis artery as a single vessel runoff to the foot, then the surgeon should consider other options.
Keys To Surgical Planning
Perioperative planning involves deciding on the optimal incision approach. Reported incisions have included a single linear, parallel linear, lazy S shape and reverse J incision.6 Authors have described an approach consisting of two parallel longitudinal incisions for the reverse extensor digitorum brevis muscle flap procedure.8 The purpose of this modification is to expose the dorsalis pedis artery and the sinus tarsi branch of the lateral tarsal artery separately to avoid donor site morbidity.
Incisions vary in part due to local vascularity and location of the recipient site. A poorly placed incision where peroneal perforators are poor or nonexistent may place the dorsal skin at risk for necrosis. A medially based incision as opposed to a laterally based incision helps avoid insult to the peroneal artery. We use a straight incision over the dorsum of the foot as this approach minimizes subcutaneous undermining.
Performing The Flap Procedure
One would perform a dorsal linear incision extending from the first web space to the origin of the extensor digitorum brevis muscle and spare the branches of the superficial peroneal nerve. Identify the medial and lateral border of the extensor digitorum longus, and mobilize these borders as a single unit. Incise the extensor digitorum brevis to the great toe to permit visualization of the dorsalis pedis artery.
Then dissect the dorsalis pedis artery distally and proximally. Identify the lateral tarsal artery and any muscular branches extending from the dorsalis pedis artery to the extensor digitorum brevis muscle and elevate these arteries along with the muscle. Take caution not to damage these vessels supplying the extensor digitorum brevis muscle. Then dissect the origin of the muscle off the calcaneus and sinus tarsi and divide the tendons. One can incorporate the fascia to add area to the muscle flap size.
Ensure that there is adequate flow by clamping the dorsalis pedis artery. The flow should not be coming primarily from the peroneal artery. To confirm the presence of retrograde flow intraoperatively, one can block the dorsalis pedis artery proximal to the lateral tarsal artery with microvascular clamps. Then evaluate the adequacy of perfusion via retrograde flow to the flap.
After deeming that perfusion is acceptable, ligate the appropriate vessels. Ligate the dorsalis pedis artery proximal to where it starts to branch out to the extensor digitorum brevis muscle. Also ligate the medial tarsal artery and any accompanying paired venae comitantes.
The length of the pedicle, when it is based on the lateral tarsal artery, typically varies from 4.8 to 7 cm.14 Typically, the pivot point is 1 cm distal to the tarsometatarsal joint. However, if more length is required, ligate the deep plantar branch and retrograde flow then occurs through the first dorsal metatarsal artery. The arc of rotation allows for coverage of the hallux. Then perform primary closure of the donor incision. After transposition of the muscle flap, one can then apply a split-thickness skin graft or delay graft placement until further wound healing occurs.
Addressing Potential Limitations Of The Flap Procedure
The main limitations to this flap include limited muscle size and sacrifice of a major blood vessel. The muscle flap may not cover the entire defect. In situations in which the muscle is smaller than anticipated and cannot cover the vital structures, then a backup plan (perhaps a free flap for example) may be necessary. In the situation with a one vessel runoff to the foot, the flap may be unreliable and/or the donor site may not heal.
The extended, distally-based extensor digitorum brevis muscle flap may be an alternative limb salvage option in select cases for osteomyelitis of the hallux in patients with diabetes.
Dr. Belczyk is a Fellow of the American College of Foot and Ankle Surgeons, and is board certified in both foot surgery and reconstructive rearfoot/ankle surgery by the American Board of Podiatric Surgery. He is a consultant physician at the Amputation Prevention Center at Valley Presbyterian Hospital in Van Nuys, Calif.
Dr. Chan is a third-year resident at White Memorial Medical Center in Los Angeles.
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