4 Primary amputation is occasionally indicated as treatment for severe lower extremity trauma. Both penetrating and blunt injuries of the lower extremities are frequently associated with vascular, nerve, bone, and extensive soft tissue injuries. Several treatment guidelines have been developed for lower extremity trauma. Lange¹⁵ recommended primary amputation for open tibial fractures with associated vascular injuries if the posterior tibial nerve was disrupted in an adult or if the duration of warm ischemia was greater than 6 hours in a crush injury. In addition, he suggested that primary amputation was relatively indicated in patients with polytrauma, severe ipsilateral foot injuries, and in those with an expected protracted postoperative course. These suggestions are supported in work by Bosse et al.¹⁶ demonstrating, in the case of high-energy lower extremity trauma, amputation, and reconstruction have equal functional outcomes at 2 years. Additional guidelines have been provided by Johansen et al.¹⁷ who devised a Mangled Extremity Severity Score to predict the need for amputation based on the extent of skeletal or soft tissue damage, limb ischemia, shock, and age. Unfortunately, none of these guidelines are predictive of functional recovery in patients who undergo limb salvage.¹⁸ Therefore, treatment with primary amputation is an extremely difficult decision and requires extensive clinical judgment as well as multidisciplinary input. Contributing factors include the severity of the injury, the overall clinical status, and the ultimate rehabilitation potential of the patient.

EVALUATION FOR REVASCULARIZATION

Modern vascular surgery techniques allow successful limb salvage in situations not previously possible. All patients who present for possible lower extremity amputation, including minor amputations, should have their peripheral vascular circulation evaluated preoperatively. Any patient with absent pedal pulses or abnormal ankle–brachial indices should be evaluated by a vascular surgeon skilled in both open and endovascular revascularization techniques. The evaluation may require only a thorough history and physical examination if there is an obvious contraindication to revascularization (e.g., nonfunctional limb, severe organic brain syndrome). Noninvasive vascular laboratory examinations are a mandatory minimum for patients with abnormal vascular examinations. Additional imaging with either multiple-slice computed tomographic angiography (CTA), magnetic resonance angiography (MRA), or contrast angiography can be done based upon the patient’s initial evaluation and vascular lab results. The information obtained from these tests is heavily dependent on the quality of the machinery, the skill of the technologist, and the knowledge of the interpreting physician. All of these factors must be taken into account when deciding which test to order. Contrast angiography with selective lower extremity injections may be necessary to fully define the patient’s anatomy and suitability for reconstruction; however, it is generally preferred to perform this invasive procedure for preoperative planning or for planned percutaneous intervention. Contrast arteriography should not be considered a diagnostic examination.

Exponential advances in endovascular techniques have occurred over the past 10 years. These have found their way into the peripheral circulation and have applicability in limb salvage. Percutaneous techniques include convention balloon angioplasty, stenting (including balloon expandable, self-expanding nitinol, and covered stents), cryoplasty, and percutaneous atherectomy (including laser, directional, and rotational). The BASIL trial showed no significant difference in amputation-free survival among patients with critical limb ischemia when randomized to open or percutaneous revascularization.¹⁹

In terms of surgical reconstruction, upper extremity²⁰ and cryopreserved cadaver vein²¹ have increased the options for conduit in limb salvage situations. Prosthetic grafts with vein cuffs^22,23 provide other alternatives when appropriate autogenous conduit is not available. More recently, a heparin-bonded prosthetic graft has been introduced and early studies show promising results.²⁴ An operation for limb salvage should never be denied only for lack of conduit.

5 Re vascularization is often performed in conjunction with a minor amputation, either simultaneously or as a staged procedure. This allows management of the acute problem of sepsis and the underlying chronic ischemia. Caution must be taken if there is active infection and the only available conduit is prosthetic for fear of infecting the graft. Amputation with control of infection followed by revascularization is the more prudent course. In extreme cases, a limited amputation can be combined with revascularization and a tissue transfer (free or rotational flap) to achieve limb salvage.^25,26

CHOICE OF AMPUTATION LEVEL

General

6 The choice of amputation level depends on the indication for the procedure, the condition of the patient, and the rehabilitation potential of the patient. The most common amputation levels are illustrated in Figure 94-1. Because most amputations are performed for complications of diabetes or arterial insufficiency, the selected level must remove all nonviable, painful tissue, allow primary healing, and maximize rehabilitation potential. Selection of the amputation level for malignant disease is dependent on the biologic characteristics of the neoplasm and will not be discussed further.

The general medical condition and the rehabilitation potential of the patient are important factors in deciding to proceed with amputation and in selecting the appropriate level. If a patient is ambulatory and independent preoperatively, the level with the greatest likelihood of maintaining function should be selected. If the patient is not ambulatory or has significant comorbid conditions, the primary wound-healing rate should be the determining factor.

Specific Situations

Aggressive attempts to salvage a distal amputation level are not indicated for patients who are unlikely to ambulate with a prosthesis.²⁷ For example, patients with fixed joint contractures greater than 15 degrees at the knee or 10 degrees at the hip are unlikely to ambulate with a prosthesis. BKAs are relatively contraindicated in patients with paraplegia because flexion contractures at the knee can lead to stump ulceration.

Energy Requirement

7 The energy required to ambulate following a lower extremity amputation increases with ascending level of amputation. The more proximal the amputation, the less likely a patient will be able to ambulate postoperatively. Table 94-2 illustrates the increased energy cost of the common lower extremity amputations. In clinical practice, the most significant increase is between a BKA and an AKA. Ambulation on an above-knee prosthesis requires the use of muscle groups poorly suited for that purpose. These increased energy costs are minor issues for young trauma or cancer patients; however, they represent a considerable obstacle for the older diabetic or vascular patient.

Clinical Assessment

The primary preoperative consideration for wound healing is the status of the skin and muscle blood flow. Operative technique, the patient’s nutritional status, and the presence of infection also affect wound healing. Clinical judgment by an experienced surgeon accurately predicts healing of a BKA in approximately 80% of cases.²⁸ A palpable pulse at the level immediately proximal to the proposed amputation essentially ensures healing;²⁹ however, the converse is not true. Noninvasive arterial testing is the most common adjunctive test used to predict healing of a specific amputation level. Its usefulness is limited when medial sclerosis prevents vessel compression, a condition common in diabetic patients. Because the digital vessels are often spared from this process, digital pressure readings may be helpful in this setting. Transcutaneous oxygen measurement has been shown to predict primary healing although it is less able to predict failure to heal.^30,31 It has become more widely available and has supplanted previous less reliable tests that were more limited in availability. Tables 94-3 to 94-6 summarize the results of various preoperative tests to predict wound healing for toe, foot and forefoot, below-knee, and AKAs, respectively.

OPERATIVE TECHNIQUE

General Considerations

Diabetic patients who present septic require adequate fluid resuscitation, broad-spectrum antibiotics (including anaerobic coverage), and an emergent operation. Whereas maintenance of limb length and function is admirable, control of sepsis and wide débridement of all nonviable tissue are essential and potentially lifesaving. All patients require atraumatic tissue handling. Avoid forceps on the skin edge. Excessive skin flaps and dead space are also not desired. Amputations done in the face of active infection are kept open and treated with dressing changes. Consider delayed primary closure in cases where perfusion is intact.

Postoperatively, the limb is elevated to minimize tissue edema and promote healing. Weight bearing on the amputation is delayed until healing is assured. This patient population requires effective prophylaxis against deep venous thrombosis and venous thromboembolism.

Digital and Ray Amputations

Digital amputations are indicated for some severe and irreducible deformities as well as gangrene or osteomyelitis localized distal to the base of the proximal phalanx. A technique for partial digital amputation is illustrated in Figure 94-2A. The circumferential or racquet-shaped skin incision is made over the distal end of the proximal phalanx, and carried down to bone. Nerves and tendons are transected under tension and allowed to retract. The proximal phalanx is divided with bone shears or power saw and the transected end smoothed with a rongeur. Soft tissue coverage can be performed with either medial/lateral flaps or dorsal/plantar flaps depending on skin tension and viability. The wound is closed only with simple interrupted skin sutures. Judicious use of subcutaneous sutures is advised due to danger of vascular compromise to the small remaining flaps. Non–weight bearing restrictions or protected weight bearing on the heel only in a rigid soled postoperative shoe or walking boot until the wound heals is recommended.

A ray amputation is indicated when the disease process extends to the metatarsal phalangeal joint. The technique is similar to a digital amputation and is illustrated in Figure 94-2B. A circumferential incision is made at the base of the involved toe and extended proximally on the dorsum of the foot over the metatarsal. The incision is extended to bone. The periosteum is cleared circumferentially and the bone is transected using a power saw at a level that will allow tension-free closure of the wound. In the case of the first or fifth toe, the incision is extended on the medial or lateral aspect of the foot, respectively. Care should be taken to bevel the distal metatarsal stump to minimize any prominence that may lead to skin breakdown with weight bearing or shoe gear wear. Typically the first metatarsal is beveled from proximal medial to distal lateral and proximal planter to distal dorsal. Metatarsals 2, 3, and 4 should be beveled from proximal plantar to distal dorsal. The 5th metatarsal is beveled from proximal lateral to distal medial and proximal plantar to distal dorsal.

In selected cases of neuropathic ulcers, the metatarsal head can be resected leaving the toe intact. A dorsal longitudinal incision is made over the metatarsal bone and the metatarsal head is resected with a power saw. Pulsed lavage and careful soft tissue inspection will help guide appropriate care for the plantar wound (i.e., packing, negative pressure therapy or ellipse of wound with closure). The dorsal wound is typically closed unless severe infection is encountered.

Transmetatarsal Amputation

Transmetatarsal amputation (TMA) is a useful procedure that maintains a patient’s ability to ambulate without the aid of a prosthesis. It is indicated when the gangrenous or infectious process involves multiple digits or a portion of the forefoot. Care must be taken to plan for the appropriate soft tissue coverage if primary closure is desired. Maximizing the plantar flap is most common, but coverage can also be gained from medial or laterally based flaps and even filleted toe flaps. If adequate soft tissue coverage is not available and a more proximal foot amputation (i.e., Chopart joint amputation) is not desired then an open amputation through the metatarsal bones can be performed. The wound is allowed to close secondarily or covered with a skin graft. Skin grafts in this position, however, are susceptible to breakdown secondary to the pressure related to ambulation.

The technique is demonstrated in Figure 94-3. A skin incision is made on the dorsum of the foot immediately proximal to the metatarsal heads and extended medially and laterally to a point midway between the plantar and dorsal surfaces. The plantar incision is made along the digital crease and extended diagonally medially and laterally to connect to the dorsal incision. The dorsal incision is deepened to the periosteum, which is cleared with a small periosteal elevator. The metatarsal bones are transected 0.5 to 1.0 cm proximal to the dorsal skin incision. The plantar flap is fashioned by continuing the dissection just superficial to the metatarsal heads. Care is taken to maintain plantar flap thickness. The nerves and tendons are transected sharply under tension and allowed to retract. The plantar flap is rotated anteriorly and assessed for length. Excess tissue is excised sharply and the deep tissue is approximated with absorbable suture. The skin is closed without tension using monofilament suture or skin staples.

Weight bearing is delayed for 1 month to allow adherence of the plantar flap. Either a soft dressing or a short leg cast can be used for a postoperative dressing.

Staging a tendo-achilles lengthening (TAL) is important to consider following (or at the same time if no infection is present) a partial foot amputation. Ulcer formation at the TMA stump site is often related to equinus formation due to the ensuing flexion/extension imbalance that occurs after resection of the forefoot. A simple triple-hemisection percutaneous TAL can effectively lengthen the achilles and reduce future pressures at the stump site.³² Other tendon-balancing procedures may be needed to control varus and valgus contraction deformities that can develop.

Syme Amputation

The Syme amputation is a foot amputation that preserves limb length and the epiphyseal growth plates, and allows occasional ambulation without a prosthesis. It is indicated in cases of extensive foot trauma or other nonviable tissue conditions distal to the hindfoot. The Syme amputation is contraindicated if a supple intact heel pad and a well-vascularized hindfoot tissue flap are not available.

The procedure can be performed in one or two stages, as illustrated in Figure 94-4. The initial steps for both procedures are identical, except that the skin incision for the two-stage procedure is located 1.5 cm more distally. The skin incision for the one-stage procedure extends from the medial to the lateral malleolus in the horizontal and vertical planes. The dorsal incision is extended to the bone, and the tendons are transected under tension. The anterior tibial artery is identified, divided, and suture ligated. The dissection is carried into the tibiotalar joint space as the foot is forcibly plantar flexed. The ligaments are transected and the talus is dislocated. The plantar aspect of the incision is deepened to the calcaneus, and the calcaneus is sharply dissected from the plantar fascia. The plantar fascia is densely adherent and care must be taken to prevent damage to the heel pad, especially at the level of the Achilles tendon. The posterior tibial artery must be preserved, because it perfuses the heel pad. The foot is then removed. The two procedures differ from this point forward.

In the one-stage procedure, the medial and lateral malleoli are transected flush with the tibiotalar joint space, and the heel pad is rotated over the ends of the tibia and fibula. The deep fascial layers are approximated with absorbable suture and the skin is closed with monofilament suture or skin staples. Securing the distal end of the remaining plantar fascia to a small drill-hole in the distal anterior tibia will help anchor the plantar flap and reduce posterior migration. In the two-stage procedure, the heel pad is similarly positioned and the wound is closed without further bone transection. In 6 weeks, elliptical incisions are made over the medial and lateral malleoli and the distal ends of the tibia and fibula are transected flush with the ankle joint. In addition, the distal flares of the tibia and fibula are transected, creating the rectangular stump of the two-stage procedure. The wound is closed in a similar fashion. For both procedures, weight bearing is delayed for at least 4 weeks to allow heel pad fixation. A soft dressing or a short leg cast can be used.

Below-Knee Amputation

The complications of diabetes and arterial insufficiency constitute most of the indications for BKAs. Tables 94-5 and 94-6 outline the criteria used to decide between a BKA and an AKA in this setting.

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