Soft Tissue Reconstruction of the Foot with a Reverse Flow Sural Artery Neurofasciocutaneous Flap

    The loss of soft tissue from the foot, either from trauma or as the result of a diabetic foot ulcer, can be a difficult problem to resolve. When tissue is lost from the weight-bearing surface of the foot, the result may be catastrophic.

The plantar soft tissues have unique functional properties integrated into the biomechanics of weight-bearing that allow them to resist external stress and protect the skeletal architecture. A full-thickness tissue loss from weight-bearing areas requires replacement with tissues whose physical properties are similar to those that were lost. Unfortunately, simple solutions such as skin grafting are unable to address problems of such complexity, and healing by secondary intention usually leads to an unstable scar in the insensate foot and a painful scar/callus complex in patients whose sensorium is intact.^1-3

    As an alternative to healing by secondary intention, several flaps have been described that can be raised on the foot and leg and used to repair defects on the weight-bearing and non-weight-bearing surfaces of the foot. These flaps have advantages over healing by secondary intention - ie, their tissue properties closely resemble those of the lost tissue and they will move harmonically with the surrounding soft tissue during weight-bearing.

    Sural artery flaps are useful in covering defects on the ankle, lower leg, and heel - areas that historically have been difficult to treat. Fasciocutaneous islands of tissue can be raised from the posterolateral surface of the leg and are based on the arteries that accompany the median branch of the sural nerve and the arterial commitantes of the lesser saphenous vein that anastomose with septocutaneous perforators from the peroneal artery.^4-7 The most distal perforator, and subsequently the most distal pivot point, is usually found approximately 5 cm proximal to the lateral malleolus.^7,8 The donor sites may be closed primarily or with a split-thickness skin graft depending on the size of the flap (see Figure 1a-1f). Other reverse flow flaps based on the major arteries of the legs have been described,^1,3 but because they required the sacrifice of a major vascular axis, they are seldom performed, even in patients without vascular disease.

    The distally-based sural island flap was first described in the early 1990s and quickly gained popularity.^8-10 Flaps that are raised on a distally-based pedicle are said to possess retrograde or reverse flow; hence, the terms reverse flow sural artery and distally-based neurofasciocutaneous sural artery are interchangeable. The technique is comparatively simple, especially as compared to a microsurgical free flap: The pedicle is raised on a wide strip of fascia, making the skeletonization rather quick. Jeng and Wei¹¹ used this technique to cover exposed Achilles tendons and soft tissue defects of the ankle and the heel. Of the 22 patients described, 20 had complete success with two minor complications that were treated uneventfully. Huisinga et al¹² used this flap on 15 patients for soft tissue coverage in the lower leg, malleolar, and heel regions; 12 flaps survived, two partially survived, and one flap failed due to persistent infection. Jeng et al¹³ reported their experience with the use of the distally-based sural artery flap for salvage of the distal foot. In seven out of eight patients, the flaps survived completely and only one patient had a partial necrosis of the flap.

    Coskunfirat et al¹⁴ performed 11 reverse neurofasciocutaneous flaps for coverage of soft tissue defects in the lower extremities. Six flaps were saphenous and five were sural; all survived completely. Bocchi et al⁸ used a reverse sural flap in 14 patients to successfully cover larger defects of the leg and ankle and a reverse adipofascial sural flap in 11 patients to cover moderate-size wounds in heel areas. Ferreira et al¹⁵ reported that in 36 distally-based superficial sural artery flaps, only six partially necrosed and no major complications occurred.

    In a larger study, Almeida et al¹⁶ performed a reverse flow island sural flap on 71 patients; 15 partially necrosed and three experienced total loss. Fraccalvieri et al¹⁷ described their experience with 18 distally-based superficial sural flaps. Only one superficial necrosis had to be surgically revised. Singh and Naasan¹⁸ used the reverse sural artery flap to treat acute open fractures of the lower leg associated with soft tissue loss. Two out of seven patients had a partial necrosis of the distal tip of the flap. Al-Qattan¹⁹ described a modified technique for harvesting a reverse sural artery flap from the upper part of the leg, and he included a gastrocnemius muscular "cuff" around the sural nerve where it perforated from deep to superficial. He suggested that this muscular cuff provided superior venous drainage of the flap.

    The use of reverse flow flaps raised from the lower leg in patients with diabetes and peripheral vascular disease may be questioned; however, in a series of patients with diabetes, the outcomes reported were quite favorable.²⁰

Methods and Materials

    A chart review was conducted of seven patients who underwent a distally-based neurofasciocutaneous sural artery flap for ankle or heel defects who had failed conservative treatment between 1999 and 2003. Chart abstraction included demographics, comorbitities, wound etiology and location, procedure performed, perioperative complications, time to return to shoes, and average healing time (see Table 1 and Table 2).

    Five of the patients had diabetes and two had a history of chronic nonhealing ulcers. The presence of a patent peroneal artery was a requirement for the patients in this study; this was determined by Doppler examination, angiogram, or magnetic resonance angiography (MRA).

Results

    Seven patients underwent repair of ankle and heel ulcers with a reverse flow sural artery neurofasciocutaneous flaps. Five patients had diabetic ulcers of the heel; one patient had developed a nonhealing ulcer of the lateral malleolus; and one patient, suffering from multiple sclerosis, had developed a chronic traumatic ulcer of the posterior heel. One of the patients with diabetes had received a renal transplant and was on immunosuppressive therapy. The flaps were raised from the posterolateral calf. In two patients, donor sites were closed primarily; in the other five patients, skin grafts were employed. All patients were discharged from the hospital with their flaps viable. One flap failed during postoperative week 2 from ischemia (in the renal transplant patient). Patients were permitted to bear weight in shoes when the flap margins were completely healed.

Discussion

    The treatment of full-thickness soft tissue defects of the foot remains problematic. The use of cutaneous and fasciocutaneous pedicle flaps offers a viable alternative to offloading and repeated debridements or amputation of the limb. The costs associated with the treatment of chronic wounds are significant in terms of professional care, hospital charges, and the outpatient costs of dressing materials and nursing visits. Pedicle flaps have been used successfully for coverage of chronic and acute large wounds of the lower extremity with certain limitations in a multimorbid patient group.^20-22 The use of biological dressings and other advanced wound therapies was not considered in these patients because of the size of the wounds and the anticipated duration of treatment or because such therapies already had been tried and had failed.

    Soft tissue defects of the hindfoot and ankle have long been viewed as troublesome because of a lack of reconstructive options available from local tissue. Large defects in this area were generally treated with free muscle flaps and skin grafts. With the development of reverse flow flaps from the lower leg, an increasing number of reports have appeared in the literature, due in large part to the simplicity of the technique, which does not require microsurgical skills.^15-24

    From a technical standpoint as well as a functional one, cutaneous or fasciocutaneous flaps may still be preferable to a distally-based sural artery flap for defects on the plantar surface of the foot. However, posterior or lateral defects of the heel and ankle are optimum locations for this flap.^25-27

    Reverse flow sural artery flaps are not without potential risks. Due to the partially ischemic state of the distal-most portions of pedicled skin flaps, it is not uncommon for patients to develop a superficial wound dehiscence at the distal end of their island flap.²⁸ This appears to be a common finding throughout most of the reported series. To minimize the risks, undermining of the flap during dissection must be prevented.

    Postoperative care requires that the flaps be monitored for ischemic changes or signs of venous congestion. During the postoperative period, protocol requires that the flap be assessed every hour by house staff or nursing. In the authors' experience, patients whose defects were posterior on the heel or over the Achilles tendon were placed on a well-padded wedge to avoid pressure from the bed or, as in two cases, skeletal traction was employed to prevent the heel from contacting the bed.

    The patient whose sural artery flap failed had type 1 diabetes, had received a kidney transplant, and was on chronic immunosuppressive therapy. This patient had been referred by a plastic surgeon who had performed a flap based on the lateral calcaneal artery and split-thickness skin graft, which had failed. This patient subsequently underwent an abductor digiti minimi flap and skin graft to cover her lateral heel. That flap remained viable until postoperative day 10 when it underwent necrosis. The sural artery flap used to salvage the foot eventually met the same fate as the previously performed procedures. A free muscle flap from the patient's latissimus dorsi in conjunction with a skin graft was ultimately used to close the patient's heel defect. This required a second application of a skin graft and 20 weeks before the patient could return to molded shoes. At the last follow-up, the patient was scheduled for a below-the-knee amputation due to an acute Charcot event that resulted in a plantar ulceration and osteomyelitis of the cuboid.

Conclusion

    Soft tissue reconstruction for chronic diabetic foot wounds should not be seen as a replacement for good traditional wound care, but rather as a viable alternative for wounds unresponsive to traditional care or for wounds with extensive exposure of bone and tendon. Most superficial ulcers can and should be treated conservatively, but clinicians should know that if conservative treatment fails, alternative therapies are available. 

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