In 1946 McKittrick described the use of the transmetatarsal amputation for the diabetic foot, along with specific indications including infection, ischemia, and neuropathic ulcerations of the toes and forefoot. He noted that forefoot amputation just proximal to the heads of the metatarsals, with primary closure, was practical only because of the introduction of penicillin for control of infection. The first transmetatarsal amputation was performed in 1944, and by 1946, 75 operations had been performed with preservation of ambulatory function. It was estimated that at least 10% to 15% of these patients would have undergone a major amputation before the use of this procedure.
Primary indications for a transmetatarsal amputation include gangrene of the digits, severe infection or abscess, chronic osteomyelitis, and nonhealing ulceration with prior digital amputation. Amputations of the hallux are most often indicated as a definitive procedure for an infected distal hallux ulcer complicated by osteomyelitis. If the infection spreads proximal to the metatarsophalengeal joint (MTPJ), a first ray resection is indicated.
Selection of an amputation level. Evaluation of perfusion, residual infection, and nutritional status are determinants in operative planning and selecting the appropriate level for amputation.
Functional foot. Assessment of the balance of forces in the foot while standing and ambulating is important to determine the ability to maintain a functional foot after healing.
Pitfalls and Danger Points
Nonfunctional amputation because of muscle and tendon imbalances or inadequate preservation of the midfoot may predispose the patient to increased pressures, subsequent ulceration, and the need for a more proximal amputation.
Excessive undermining of tissue, harsh handling of tissue, inadequate removal of nonviable or infected tissue, and poor hemostasis leading to hematoma may all contribute to necrosis of the incision.
Selection of an Amputation Level
Determining the level at which to amputate is not always obvious. In emergent situations appropriate debridement is essential, and the extent of infection initially dictates the level of debridement and amputation. Concerns of reconstruction and function should not discourage the surgeon from removing all infected tissue. After infection is controlled, it is important to determine the level of adequate tissue perfusion and tissue coverage of the defects. Physical examination augmented by noninvasive vascular studies, tests of tissue oxygenation or perfusion, and angiography help determine the need for vascular surgical intervention and the ultimate level of amputation healing.
The goals of a partial foot amputation are to first control infection and then perform the most distal, functional amputation. In the presence of an infection, the amputation is often performed in two stages. Certain lower-level, foot-sparing amputations are generally better tolerated and result in a more functional outcome than do higher-level amputations.
Choice of Anesthesia
All forefoot amputations may be performed under local, regional, or general anesthesia.
Proper surgical technique is paramount to reducing the risk of complications. Procedures are generally performed without a tourniquet to help determine tissue viability, because all necrotic tissue must be removed. Skin incisions are made full thickness with minimal undermining. Medial and lateral incisions should be performed at the glabrous juncture between the dorsal and the plantar circulation. Dorsal and plantar incisions should be to bone, without undermining the soft tissue, to preserve arterial perfusion and thick soft-tissue coverage. Meticulous handling of the skin is essential, and a “no-touch” technique is used to prevent further injury. The area is irrigated, and deep tissue cultures are obtained using sterile, unused instrumentation as indicated.
A fish-mouth incision is made proximal to all infected and nonviable tissue. The plantar skin incision extends farther distal to preserve a plantar soft-tissue flap so that the final suture line lies on the dorsal aspect of the stump ( Fig. 52-1 , A ).