LOCAL FLAPS FOR FOREFOOT AND MIDFOOT RECONSTRUCTION

JAMES A. PARKER, MD, and JOHN M. SEARLES, JR, MD

Reconstruction of the foot can be a challenging and rewarding endeavor. Knowledge of underlying medical problems and mechanical causes of wounds of the forefoot and midfoot are essential for a successful outcome. A diligent preoperative examination and workup are paramount in choosing the appropriate therapy. The degree of vascular patency must be assessed before any definitive reconstruction is undertaken. Adequate debridement and wound care are paramount. Coverage of the dorsal and plantar, forefoot, and midfoot wounds can be performed with a variety of techniques. Meticulous surgical technique, as well as attention to mechanical or medical causes for recurrence, are the final cornerstones of successful reconstruction of the foot. Copyright �9 1997 by W.B. Saunders Company

KEY WORDS: forefoot reconstruction, midfoot reconstruction, dorsal foot reconstruction

The foot plays an important role in support during standing and the mechanics of walking. Many pathological processes may have detrimental effects on the foot's ability to adequately perform its designed function. The bones of the foot, the joints, the soft tissues surrounding the foot, and adequate sensory feedback are essential to normal ambulation. Peripheral vascular disease, diabetes mellitus, rheumatoid arthritis, and collagen vascular diseases are a few of the disease processes that can disturb the normal functions of the foot.

W O U N D E V A L U A T I O N

Evaluation of the foot wound should not only encompass the wound itself but also the underlying cause of the wound. History of trauma to the foot may be easily elucidated; underlying medical problems that predispose to poor wound healing must also be investigated. Patient history of diabetes, hypertension, and/or chronic or poor wound healing should alert the surgeon to the possibility of wound healing problems.

V a s c u l a r Evaluation

As with any problem encountered, a detailed physical examination should be performed. Presence or absence of pedal pulses as well as pulses higher in the extremity should be noted. Local inflammatory responses may blunt pulses or make evaluation difficult, and in such instances, numerous noninvasive studies can be done to assess the inflow to the extremity. An ankle/brachial index is easily

From the Section of Plastic Surgery, University of Kansas Medical Center, Kansas City, KS.

Address reprint requests to John M. Searles, Jr, MD, Section of Plastic Surgery, University of Kansas Medical Center, 3901 Rainbow Blvd, Kansas City, KS 66160-7389.

Copyright �9 1997 by W.B. Saunders Company 1071-0949/97/0404-0001 $5.00/0

performed and provides a relative indication of ischemia. Absolute pressures of less than 50 mm Hg signify severe arterial inflow obstruction and correlate with poor wound healing. 1 However, neither the absolute pressure nor the ankle/brachial indices are always accurate. 2 Noncompress- ible arterial walls caused by medial calcification may be seen in up to 30% of patients with diabetes mellitus and can cause a falsely elevated pressure for either value. Many authors have demonstrated the ability of toe pressures to accurately predict the likelihood of wound healing. 3-5 Absolute values of 20 to 30 mm Hg represent severe ischemia and require vascular inflow augmentation to allow healing. 6

Directional Doppler studies are of utmost importance in assessing peripheral circulation and have become our most important means of vascular evaluation. Distal to an arterial stenosis or occlusion, the normal triphasic wave- form becomes abnormal. The waveform is dampened, the amplitude of the velocity wave is decreased, the peak is delayed, and the reverse component is attenuated or absent. Patients with triphasic or biphasic waveforms in the posterior tibial artery normally do not require any inflow augmentation if local flaps are to be used, whereas those with monophasic waveforms may or may not need improved vascular ingress if local flaps are to be success- ful. Transcutaneous oxygen membrane potentials (Tcomps) are being used to accurately predict the success of local flaps, skin grafts, or other secondary techniques in patients with monophasic waveforms. 7-1~ In studies done on patients with foot ulcers, nearly all ulcers healed in patients with Tcomps of 25 mm Hg or greater, although we prefer readings of at least 40 mm Hg contiguous to the wound.

Angiography has been the historical gold standard for evaluation of peripheral circulation. Angiography is essen- tial in the event that any vascular intervention is required. An angiogram delineates important anatomic information

148 Operative Techniques in Plastic and Reconstructive Surgery,, Vol 4, No 4 (November), 1997: pp 148-156

Fig 1. (A) Fifth metatarsal head ulcer. (B) Metatarsal resection. (C) Flap elevation. (D) Long-term appearance.

about vessel patency, directional blood flow, and distal run-off. The qualitative and quantitative physiological effects of diseased segments can best be assessed by the use of duplex imaging.

Wound Management

The fundamentals of wound care are as important in foot wounds as they are in any other wound. Patients present- ing with overt cellulitis must be placed at bedrest with the extremity elevated. Drainage of gross purulence and aggres- sive debridement of devitalized tissue are essential. A high index of suspicion should be held for plantar abscesses in diabetic patients as these may be limb-threatening if missed. Aspiration with an 18-gauge needle in the subfas- cial space is diagnostic. Implementation of broad-spectrum antibiotics that cover both aerobes and anaerobes should

immediately start while wound and tissue cultures are pending. After adequate debridement, the use of topical, broad-spectrum antibacterials (Silvadene [Marion Merrell Don Inc., Kansas City, MO] twice daily) can help keep the bacterial count down. For patients presenting with wounds without gross cellulitis or infection, single-staged debride- ment and closure with local flaps can be performed safely and successfully given adequate arterial flow through the posterior tibial artery. For wounds with gross infection, closure should be delayed for 3 to 5 days after debride- ment, drainage, and initiation of antibiotic therapy.

RECONSTRUCTION

Reconstruction of the foot remains complex and challeng- ing; the goal of the surgeon should be to attain a closed

FOREFOOT AND MIDFOOT RECONSTRUCTION 1 4 9

Fig 2. (A) Large forefoot ulcer after transmetatarsal amputa- tion. (B) Two opposing flaps ready for advancement. (C) Immediate postoperative result.

wound and to provide for bipedal ambulation. Skin grafts, limited amputations, local flaps, and free tissue transfers must be in the armamentarium of the plastic surgeon.

Certain basic principles must be adhered to in order to attain a satisfactory result with local flap reconstruction. If possible, some degree of protective sensation should be

provided in reconstruction. In planning the reconstruction, the underlying bony framework and its weight-bearing characteristics must be evaluated. Causes of a weight maldistribution, such as bone spurs or joint dislocations, must be corrected to maintain a stable soft-tissue coverage. Most importantly, the presence or absence of peripheral vascular disease must be ascertained. As stated, all the

1 5 0 PARKER AND SEARLES

flaps suitable for plantar foot closure in the fore and midfoot are dependent upon antegrade flow through the posterior tibial artery and its medial and lateral plantar vessels.

In general skin-grafting techniques are best reserved for shallow defects on non-weight-bearing surfaces. Split- thickness skin grafts used on the plantar weight-bearing surface are usually unstable over prolonged follow-up. About 50% of cases require further reconstruction. I1-I3 Bone devoid of periosteum, tendon, or paratenon will not accept a skin graft and thus require flap closure.

Foot Dorsum

Shallow wounds on the dorsum of the foot with intact paratenon are amenable to closure with split-thickness skin grafts. Depending on the associated medical problems of the patient, excision of tendons with involved paratenon may be preferable to free tissue transfer because it allows split-thickness skin grafting directly onto the periosteum of the metatarsals. The abductor hallucis muscle, with or without the medial head of the flexor hallucis brevis muscle, and the abductor digiti minimi muscle, have been used for closing small wounds on the proximal dorsal foot. TM The blood supply originates from the posterior tibial artery, and its patency must be confirmed before proceed- ing.

The extensor digitorum brevis muscle may be moved proximally to cover proximal dorsal foot wounds. The blood supply to the muscle is derived from the lateral tarsal artery, which is a branch of the dorsalis pedis artery at the level of the distal edge of the extensor retinaculum. Thus, antegrade blood flow through the anterior tibial- dorsalis pedis artery needs to be confirmed. Exposure is obtained through a dorsal incision that communicates with the wound. The dorsalis pedis pedicle is divided distal to the origin of the lateral tarsal vessels to provide the arc of rotation needed and to allow transposition of the muscle. The long extensors are dissected off the underlying short extensor muscle slips. The dorsalis pedis artery and its veins are divided distal to the extensor digitorum brevis. The medial tarsal branches are ligated as the dissection proceeds proximally. The lateral tarsal vessel, along with the muscle, is elevated while the origin and tendonous extensions of the muscle are divided. 15 The four slips of muscle, measuring 4.5 • 6 cm, are broad and thin and thus are useful for smaller wounds. Is Larger wounds with exposed bone or tendon located on the dorsum of the foot may require free tissue transfer for coverage.

Plantar Forefoot

The surgical treatment of forefoot wounds is based on location. Infection or severe injury to a single toe is best managed by amputation, provided preoperative vascular workup has established adequate blood flow to heal the amputation. A ray amputation (digit plus associated meta- tarsal) may be indicated in order to remove all devitalized or infected bone. The plantar and dorsal flaps of the toe skin are often all that is necessary for primary closure. If

additional skin is required, an adjacent toe may be filleted and transposed for closure.

Numerous techniques that make use of transposition of local tissues have been described. Our most frequently used technique is to advance forefoot skin, fat, and fascia in a V-Y fashion to close small defects (Fig 1). Double opposing flaps may be designed to close defects up to 4 cm in diameter 16 (Fig 2). Cadaveric studies using latex injec- tions have identified numerous perforating vessels arising vertically throughout the plantar aspect of the foot (Fig 3). Mobilization of the flap is done under tourniquet control and requires release of the plantar fascia around the perimeter of the flap, as well as release of the vertical slips of fascia that attach the skin to the underlying metatarsals. Adequate debridement and care of the underlying bony abnormalities are essential to long-term success. When ulceration occurs over the fifth metatarsal head, resection through the metatarsal neck is recommended. With ulcer- ation over the second, third, or fourth metatarsal heads, one should perform a metatarsal neck osteotomy at the time of wound closure. This procedure is done through a

Fig 3. Location of multiple cutaneous vascular perforating vessels on plantar surface of foot,

FOREFOOT AND MIDFOOT RECONSTRUCTION 1 51

Fig 4. (A) Dorsal approach for metatarsal head osteotomy. (B) Wound closed. Single K-wire in place.

dorsal approach and allows the prominent metatarsal head to move dorsally without excessive weight transfer to the adjacent metatarsals. The metatarsal head is held in place by a single Kirschner wire (Fig 4).

The neurovascular island flap of a filleted toe, originally described by Moberg, v is a useful technique for forefoot coverage. The procedure is best performed under tourni- quet control while the plantar wound is debrided and an outline of the adjacent plantar toe flap is designed. When the metatarsal head is being closed with the soft tissue from the associated toe, dissection of the island is not necessary, because simply removing the bony framework will provide enough mobilization to cover the defect} 8-2~ Elevation begins distally off the distal phalynx and flexor tendons. Identification of the medial and lateral neurovas- cular bundles in the web spaces is paramount in maintain- ing sensation in the flap. The bony support is then disarticulated at the metatarsophalangeal joint, and the dorsal skin is used to close the donor site. The tourniquet is deflated; hemostasis is obtained; and the wound is closed with the resultant flap.

A neurovascular island flap from the lateral aspect of the great toe can be taken without sacrifice of the toe itself (Fig 5). Depending on the dimensions of the flap, the donor site may be closed primarily or with a split-thickness skin graft. The flap is elevated on the lateral plantar aspect of the great toe at the level of the phalangeal periosteum. The neurovascular bundle may be dissected into the web space should additional length be required. An incision connect- ing the wound and the web space is made to allow transposition of the flap. This technique is effective for wounds 2 to 3 cm in diameter.

Plantar Midfoot

Small wounds in the midfoot region are amenable to closure with any of the techniques described for the forefoot. Split-thickness skin grafts may be used in true non-weight-bearing areas. For this to be an option, the transverse arch must still be present. The neurovascular island flaps may be employed for 2 to 3 crn defects (Fig 6). This procedure obviously requires a more proximal dissec- tion of the nerves and vascular supply of the plantar surface of the foot. As in the forefoot, individually fash- ioned V-Y advancement flaps are oftentimes the simplest method of reconstruction (Fig 7). Bony prominences associ- ated with midfoot wounds should be addressed with judicious resection. The medial instep wound results from deformity about the first metatarsal base, medial cunei- form, and navicular bones. The lateral wounds seen are usually secondary to prominences of the fifth metatarsal base and cuboid bones.

Another alternative for midfoot reconstruction is a me- dial- or lateral-based plantar flap 21,22 (Fig 8). Medially based flaps are raised by incising laterally and elevating the subcutaneous tissue off the abductor digiti minimi muscle. Dissection is carried mediall3~ which allows identi- fication and preservation of the cutaneous branches of the lateral plantar nerve as they emerge from between the abductor and the plantar fascia. Arterial branches to the skin are divided to further facilitate the isolation of the nerve. Branches of the medial plantar nerve are seen coursing into the flap from between the abductor hallucis muscle and the plantar fascia. As the flap is elevated

152 PARKER AND SEARLES

Fig 5. (A) Ulceration over second metatarsal head. (B) Neurovascular island flap from lateral side of great toe is elevated. (C) Appearance after flap inset and donor site closure with split-thickness skin graft harvested from non-weight-bearing arch of foot, (D) Long-term appearance,

proximally, the medial and lateral plantar nerve branches are separated from the main trunk for a short distance to preserve sensation without sacrificing flap mobility. For the laterally based flap, a similar dissection is carried out, but the branches of the medial plantar artery are sacrificed to allow rotation.

Wounds greater than 4 to 5 cm generally require some form of free tissue transfer or an amputation to pro- vide long-term soft tissue coverage. It is important to try to maintain foot length at the midfoot level so that orthotics rather than prostheses may be used postopera- tively.

FOREFOOT AND MIDFOOT RECONSTRUCTION 1 5 3

Fig 6. (A) Medial plantar ulcer, (B) Elevation and proximal dissection of neurovascular island flap. (C) Long-term closure,

COMMENTARY

Doctors Parker and Searles have succinctly reviewed the most reliable options for closing wounds of the forefoot and midfoot regions. They include the all-important assess- ment of the underlying bone and tendon abnormalities that often contribute to the formation of these indolent ulcerations, and they underscore the importance of address- ing them as part of the reconstructive plan. Plastic sur- geons must be adept at all the procedures outlined. In addition they must be able to perform toe amputation (with or without the associated metatarsal), forefoot ampu-

tation (transmetatarsal), and midfoot amputation (Lisfranc and /o r Chopart) to adequately address the wide range of wounds and comorbid disease that may be seen in this area.

In the diabetic neuropathy patient, the most commonly seen patient with forefoot or midfoot disease, the adjuvant use of Achilles' tendon lengthening has significantly de- creased the incidence of recurrent ulceration. By decreas- ing the load borne by these anatomic locations during ambulation, in combination with the removal of the under- lying bony prominence, recurrence has been less than 2% when followed-up for more than 5 years.

Fig 7. (A) Lateral midfoot wound after debridement of soft tissue and underlying cuboid. (B) Closure accomplished with a V-Y advancement flap.

154 PARKER AND SEARLES

Fig 8. (A) Chronic wound lateral midfoot. (B) Flap design following debridement of soft tissue and cuboid bone. (C) Rotation of flap into wound. (D) View 1 year following reconstruction,

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