Extensor Digitorum Brevis and Extensor Hallucis Brevis Flaps

The extensor brevis muscle gained popularity based on its reliability in covering lower extremity wounds. It is small, measuring 4.0 X 6.0 centimeters.   However, it has a reliable vascular pedicle and when elevated as a rotational¹ or island flap^{2, 3} can provide stable coverage of the distal foot and anterior, medial, or lateral ankle: areas which are not reliably covered by the calf muscles when based distally.

The extensor brevis muscle has also been harvested and utilized as a microvascular muscle transplant to provide coverage⁴ for open wounds or, if taken with its motor nerve, to restore function^5-7.  In this situation, its pliability, small size, and reliable neurovascular pedicle make it particularly useful for reconstruction of the hand and face areas, which suffer from reconstruction with tissue, which is not pliable or or often too bulky. The extensor hallucis brevis can be harvested separately based on its own neurovascular pedicle or in combination with the extensor digitorum brevis slips.

Although the flap is reliable, the donor site may not be. Harvest of this flap usually requires sacrifice of the dorsalis pedis artery, although harvest of the flap sparing the dorsalis pedis artery has been described.⁸  In general, care must be taken to insure that collateral blood supply to the foot exists. This can be demonstrated with dorsalis pedis compression and first dorsal metatarsal artery monitoring with a pencil doppler probe.  Even in the presence of a patent vascular arch and meticulous handling of the tissues, wound break-down is not an uncommon complication of this flap.⁹

The advent of microsurgical techniques, morbidity of the donor site, and the small size of this muscle have combined to narrow indications for the extensor brevis muscle as a local flap or microvascular transplantation.

Anatomy

The extensor brevis muscle is composed of four slips (Fig. 1). The body of this muscle originates on the talo-calcaneal ligament and the inferior calcaneus on the lateral foot. The extensor hallucis brevis, the most medial slip inserts on the proximal phalanx of the great toe. The extensor digitorum brevis, the lateral three slips insert on the second, third, and fourth toe extensor tendons. This muscle lies just under the long extensor tendons to the toes and just above the navicular, cuneiform, and metatarsal bones.

The lateral tarsal artery, a branch from the dorsalis pedis artery supplies the extensor hallucis brevis and extensor digitorum brevis muscles. It originates under the extensor retinaculum and enters at the junction of the proximal and middle thirds of the muscle belly.

A branch of the deep peroneal nerve innervates the extensor brevis muscle. Again, this branch parallels the course of the lateral tarsal artery and enters at the junction of the proximal and middle thirds of the muscle belly. Although this nerve branch is short, intraneural dissection under microscopic magnification allows additional length.

Dissection

Harvest of the muscle is performed with the patient in the supine position. A two-team approach is easily available given the peripheral location of this flap. Dissection should proceed after identifying and marking useful anatomic landmarks. The course of the dorsalis pedis artery should be identified by doppler probe. Palpation while the patient extends the toes readily identifies the body of the muscle over the lateral cuneiform bone of the foot.

An incision beginning just lateral to the anterior tibialis pulse at the ankle and extending in a lazy S shape onto the dorsum of the foot is diagramed (Fig. 2). Dissection is performed under tourniquet control. Branches of the superficial saphenous system are ligated as necessary. The skin flaps are developed in a plane just above the peri-tenon of the extensor tendons, which preserves the vascular integrity of the skin flaps and peri-tenon of the extensor tendons.

The long extensor tendons can be retracted exposing the short extensors and muscle bellies. The extensor hallucis brevis tendon is then elevated and retracted from where it crosses the first metatarsal space exposing the dorsalis pedis artery, venae, and deep peroneal nerve. 

The extensor brevis tendon insertions are identified and transected. They are then controlled as a group so that individual muscle bellies are not avulsed one from the next. 

The dorsalis pedis artery, venae, and deep peroneal nerve are then dissected proximally while elevating the muscle bellies. Care is taken to identify the neurovascualr pedicle as they enter the medial edge of the muscle belly. As the dissection progresses the muscle can be turned over offering better visualization and protection of the neurovascular pedicle (Fig. 3). After the muscle origin is taken down dissection along the dorsalis pedis artery and venae can obtain additional arterial length.  If additional nerve length for functional muscle reconstruction is required, then under microscopic magnification, intra-neural dissection can be performed along the deep peroneal nerve.

The tourniquet is released to re-establish and confirm circulation to the muscle.  After hemostasis is obtained, the donor site is closed over drains to keep blood from accumulating under the skin flaps. 

Post-Operative Care

The leg is strictly elevated for two weeks. After that point, compression with an Ace bandage is employed whenever the leg is dependent for an additional two weeks.

Bibliography

1. Barfred N, Reumert T. Myoplasty for covering exposed bone or joint on the lower leg. Acta Orthop Scand 44:532, 1973.

2. Leitner DW, Gordon L, Buncke HJ. The extensor digitorum brevis as a muscle island flap. Plast Reconstru Surg 76:777, 1985.

3. Bakhach J, Demiri D, Chahidi N, Baudaet J. Distal extensor digitorum muscle flap: new refinements. Plast Reconstr Surg 102:103-112, 1998.

4. Buncke HJ, Hing DN. Extensor digitorum and hallucis brevis muscle transplantation and application as an island flap. In Buncke HJ, ed. Microsurgical transplantation-replantation an atlas-text. Philadelphia: Lea Febinger 1991:696-714.

5. Tamai S, Fukui A, Shimizu T, Yamaguchi T. Thumb reconstruction with an iliac bone graft and a dorsalis pedis flap transplant including the extensor digitorum brevis muscle for restoring opposition: A case report. Microsurgery 4:81, 1983

6. Tolhurst DE, Bos KE. Free revacularized muscle graft in facial palsy. Plast Reconstr Surg 69:700, 1982.

7. Tulley P, Webb A, Chana JS, Tan ST, Hudson D, Grobbelaar AO, Harrison DH. Paralysis of the marginal mandibular branch of the facial nerve: treatment options. Br J Plast Surg 53:378-85, 2000.
   del Pinal F, Herrere F. Extensor digitorum brevis free flap: anatomic study and further clinical applications. Plast Reconstr Surg 105:1347-56, 2000.

8. Pai CH, Lin GT, Lin SD, Lai CS. Extensor digitorum brevis rotational muscle flap for lower extremity ankle coverage. J Trauma 49:1012-16, 2000.