Amputations of the Foot and Ankle

Tourniquets

Tourniquets are frequently used in amputation surgery. They allow for a bloodless field, allowing identification of relevant anatomy, without affecting wound healing. A controlled, randomized trial of tourniquet use in foot amputations in diabetic and dysvascular nondiabetic patients demonstrated no difference in healing rates between patients with tourniquets and those who did not have tourniquets applied. In this series, the tourniquet was released once the amputated part was removed, before beginning the closure, to check for hemostasis and flap viability.

Use of tourniquets requires three other considerations: the location, the type of tourniquet, and the presence of underlying vascular bypass grafts. For partial foot amputations, if a tourniquet is desired or needed, an Esmarch bandage just above the malleoli has been shown to be safe and effective, although use of a calf tourniquet is also common. For more proximal amputations, a thigh tourniquet is required. Although easy to use, thigh tourniquets can inhibit quadriceps function postoperatively, which may be a consideration in some patients. Surgeons are reluctant to place a tourniquet over this area in patients with vascular bypass grafts.

In the case of below-knee amputations, it is reasonable and very often helpful to use a thigh tourniquet to improve visualization, especially for ligature of the vascular bundles and identification of nerves. The tourniquet is released before wound closure to verify hemostasis.

Soft Tissue Preservation

The most important first step in amputation surgery is aggressive resection of infected and necrotic bone and soft tissue. This must be balanced by the need to preserve the maximum amount of viable skin and soft tissue. This is especially the case with plantar flaps because the plantar tissue offers the best soft tissue coverage of weight-bearing surfaces. There needs to be a balance between the need to perform an aggressive resection of necrotic tissue and the need to preserve tissue.

For this reason, many amputations used to treat gangrene and uncontrolled infection are performed in a staged manner. The first stage procedure focuses on eradication of the infection, which may require one or more surgeries. The second phase is reconstructive, focusing on closing the wound and obtaining a functional amputation for ambulation. In first stage amputations performed for gangrene, the initial and preliminary line of resection should be quite close, usually a few millimeters, from the edge of the gangrene. This is done to save the maximum amount of soft tissue. Taking a too-generous margin of skin at the first debridement often can force the surgeon to go to the next higher level of amputation. However, if additional necrosis develops, further debridements are performed until all tissue is viable.

During the second phase surgery for closure, if the wound edge proves not to be viable, it can be resected back farther. Surprisingly, the skin and soft tissue is usually viable because the level of nonviability has already been demarcated by the gangrene. In many cases, the focus of infection involving the foot is sufficiently distal or localized that the amputation, debridement, and wound closure can be done in a single session.

The surgeon should not hesitate to make irregular or asymmetric flaps and then to reevaluate the pattern of closure once a bleeding edge has been obtained all around the wound. The surgeon must make the best use of the available soft tissue and is encouraged to use “creative” local flaps. The principle is to make use of the areas of viable tissue that might not fit the pattern of a standard flap for the level of amputation. Otherwise, the patient has the disadvantage of requiring a more proximal amputation. For example, the pattern of locally viable tissue might allow the surgeon to swing a local flap medially to laterally instead of using the typical long plantar flap for closure of a transmetatarsal amputation. This type of local flap is also preferable to a skin graft because it is more durable and more sensate. Classically, the ideal length of the flap is approximately half the width of its base. However, the real-life situation of patient care is not always ideal, and some allowance must be made for the vagaries of each case if it affords a potential advantage to the patient.

Residual local flaps often need to be thinned, especially where they form corners. This is true at all levels of amputation. As the excessively thick flap is folded over, it bunches up in the corner and pushes the skin edges away from each other. Thinning the flap excessively can disturb the vascularity of the skin edge. Some residual thickness contributes to a natural eversion of the edges.

Wound Closure

The final wound, especially in a partial amputation of the foot, must be fashioned to balance the length of preserved bone with the available soft tissue to cover it. Wound closure, and thus the ultimate length of the foot, is almost always a function of the amount, location, and shape of the remaining viable soft tissue. If there is deep infection of the bone, the overlying soft tissue is usually compromised by infection as well. Once both are resected to a level proximal to the infection, the bone length can be balanced to the soft tissue.

In many cases, it is necessary to sacrifice an additional portion of the osseous structure to achieve this balance. In an infected diabetic foot, this can necessitate excision of additional uninfected bones to achieve delayed primary closure of a partial forefoot or transmetatarsal amputation. An example of this scenario is a patient in whom the medial two or three rays have been partially resected for osteomyelitis, and the remaining lateral rays create an insufficient platform for weight bearing. In this situation partial resection of the uninfected metatarsals may allow a better balanced and more functional foot.

Once a clean, granulating wound is achieved, the wound should be closed. Although primary closure cannot always be achieved, especially in the dysvascular or diabetic patient, the surgeon should strive for primary closure of the amputation site. This can be either an immediate primary closure at the time of amputation or a delayed primary closure following a later wound debridement procedure.

Failure to achieve primary or delayed primary closure in a large number of cases signifies poor decision making. Leaving large gaping wounds to granulate inward as the main method of healing amputations, especially in diabetic patients, condemns the patient to an unnecessarily and very long recovery ( Fig. 34-2 ). An attempt at prolonged stump healing by secondary intention often represents the surgeon's failure to make the correct decision about the viability of the local tissue and the appropriate final level of healing. It is more clinically effective and less debilitating to the patient to establish the vascularity and healing potential of the partial foot amputation wound and then perform a definitive procedure with good, viable local closure. If needed, the limb should first be revascularized by the vascular surgeon, then redebrided, and eventually closed at the new level of viability.

Allowing an entire amputation wound to granulate is an extremely slow process; therefore delayed primary closure is valuable, even if it only achieves partial closure of the wound. It reduces the amount of coverage to be achieved and speeds healing. In such cases, the wound flaps adhere over part of the wound's length, and a portion fails to close and continues to drain small amounts. However, this still reduces the morbidity because the residual wound that must granulate inward is still only a fraction of the original wound's size. The validity of this concept has been aided by the advent of negative-pressure wound dressings. The technique of performing a partial delayed primary closure combined with the use of a negative-pressure wound dressing does not work for every case, and it certainly cannot overcome inadequate debridement or inclusion of nonviable soft tissue. However, primary closure, even when partial, is a durable technique for maximizing foot salvage.

The use of negative pressure wound dressings or “wound vacs” has provided a powerful tool to facilitated wound healing. A sterile sponge-like dressing combined with constant or intermittent negative pressure applied within a closed (vacuum sealed) environment allows exudate to be removed from the wound area and encourages tissue oxygenation. In the case of open wounds this encourages healthy wound granulation and, when applied to a primarily closed wound, can help facilitate the wound to heal. The closed, sterile nature of the wound dressing helps keep the wound clean and can help stabilize a wound prior to performing a delayed primary closure, or sequential wound vacs can be placed to help facilitate wound healing via secondary intention.

If partial closure is achieved, the time to complete healing is greatly reduced. A common pattern is adherence and closure of the two ends of the suture line, with a small area in the middle third left unopposed. The sutures in the healing areas are usually left in place for a minimum of 4 to 6 weeks, occasionally longer, while wound care continues on the central portion of the wound. This is an important consideration because the entire wound in a diabetic or dysvascular patient can take many months to granulate inward.

There are several possible explanations for a wound that does not appear ready for delayed primary closure. The initial debridement might have been inadequate, and nonviable tissue remains. The soft tissue flaps might have inadequate vascularity. Or the wound might have had insufficient time to begin granulating. Even if it is decided to cover the wound with a split-thickness skin graft, a good granulating base, or well-vascularized tissue (e.g., muscle), is necessary first.

In amputation closures, the skin edges should be handled as little as possible. Forceps should be used on the subcutaneous and deeper layers, rather than on the skin edges. Flaps should be tested at closure by gently bringing them together manually without tension. If such a closure cannot be completed, more of the underlying bone must be resected to reduce the pressure on the flaps. The stump should be palpated through the flaps to make sure that no rough edges, sharp angles, or undesirable bony prominences remain. The balance of soft tissue to bone discussed earlier is most evident at closure because there should be no tension on the skin edges or suture line. Skin blanching is a sign of an overly tight closure. In diabetic amputations, the nylon skin sutures, which are nonreactive, should be left in place a minimum of 4 weeks, and sometimes longer.

It is not necessary to resect the cartilage from the exposed bony surfaces at the level of the amputation. Preservation of the cartilage, and thus of the underlying subchondral bone, can create a barrier to infection of the residual bone. Additionally, the clearly defined line of the subchondral bone makes it easier to follow the postoperative radiographs for changes such as erosion of the distal bone.

Drains

Drains should be used at the time of the amputation stump closure if there is a chance of a fluid collection forming in the deep and subcutaneous tissue. If the wound does not demonstrate a propensity for fluid collection, an incisional wound vac or a simple sterile dressing may be used. However, as many amputation wounds have residual bleeding from bones and other tissue, the need for some form of suction drain is common. The type of drain depends on the surgeon's judgment, the configuration of the wound, and the characteristics of the wound closure. Ideally, a closed suction drain should exit through a small stab wound separate from the primary wound. Penrose drains, which typically exit through the closure and between the sutures, are discouraged. They tend to interfere with early adherence of the wound edges in that location and are less effective than a suction drain in reducing postoperative collection of fluid or hematoma.

Skin Grafting and Flap Coverage

Skin grafting is an acceptable technique for obtaining coverage (as distinguished from closure) of amputation wounds. Split-thickness grafting is somewhat more successful in traumatic amputations than in those done in insensate diabetic feet. Because of the loss of protective sensation, primary closure with local soft tissue flaps is still preferable in diabetic patients. Skin grafts can make the difference between salvage and loss of an amputation stump, but they have a higher rate of recurrent breakdown than local skin coverage.

Free tissue transfer has been a valuable adjunct to limb salvage, especially in traumatic amputations of the foot. Common free tissue transfers include: anterolateral thigh flap, parascapular flap, radial forearm flap, or latissimus dorsi flap. The greatest benefit of a free flap has been the ability to obtain soft-tissue coverage over wounds of the ankle, heel, and hindfoot. These areas have relatively little subcutaneous tissue, and the skin, especially in the hindfoot, is fixed and immobile, which makes rotation of local flaps difficult. However, free tissue transfers are difficult, and they add time, expense, and morbidity to the patient's recovery. Their use should thus be thoughtfully justified. In general, the technique is not often applicable to the forefoot and midfoot. However, when appropriately indicated for coverage of a soft tissue defect over the hindfoot or heel, a free tissue transfer has the potential to create a great difference in functional outcome. The dramatic effect is often credited with converting the patient who has no heel from being a user of a prosthesis (e.g., a Syme ankle disarticulation or below-knee amputee) to being a user of a shoe.

Vascular Reconstruction

Limb revascularization is often the key to salvage of the foot. Preoperatively, pulses, ankle-brachial index, or arterial doppler ultrasound should be checked, as discussed below. During an amputation in a diabetic or dysvascular limb, the skin edges should be checked once the final flaps have been fashioned. Typically, the surgeon checks for the presence of punctate bleeding spots in the flaps and especially along the skin edges. If there is not at least a small amount of visible bleeding, the flaps may need to be revised to a more proximal level. When the limb is dysvascular, vascular consultation should be obtained. Revascularization of the limb can be done through angioplasty, placement of a proximal stent, endarterectomy, proximal bypass, or distal bypass surgery. The emphasis should be on doing the revascularization before fashioning the final amputation flaps. Preferably, the final level of amputation is determined once maximum tissue perfusion has been achieved.

Bypass is the most common of these revascularization techniques. Balloon angioplasty is applicable primarily to discrete, well-localized (and usually proximal) occlusive lesions. These discrete occlusive lesions are relatively uncommon in diabetic patients and more common above the popliteal artery in nondiabetic vascular disease. In the nondiabetic patient, bypass usually takes the form of proximal bypass of a major occlusion at the iliac, femoral, or popliteal levels. In the dysvascular diabetic patient, similar proximal occlusions or stenoses occur and respond well to a vascular bypass. In addition, and very commonly, diffuse occlusions of the arteries distal to the trifurcation of the popliteal artery can occur in the lower part of the leg. Unlike in the nondiabetic patient, these are not discrete blockages but usually consist of atherosclerotic involvement diffusely through the vessel. Bypass done down to the level of the ankle may use in situ or reversed saphenous vein grafts.

The customary surgical techniques described here are basic guidelines, not absolute requisites, for successful amputations. No matter what the conscientious surgeon does, some amputations will fail and will need to be revised to a higher level. If every amputation heals primarily, the surgeon may be doing some amputations at too-proximal a level and not achieving enough salvaged cases from the feet. Often, several procedures and revisions are needed before the final result is obtained. The need for a revision amputation does not substantially effect the quality of the ultimate result and therefore surgeons should make an attempt to maximize foot salvage based on their clinical assessment. Healed amputations that result from revision procedures yield satisfactory results similar to those that heal after a single level of amputation. Once partial amputations of the foot heal, the reported rate of revision is as low as 10%, thus indicating that these function as definitive procedures. Surgeons needs to use imaging and laboratory data, clinical experience, and surgical judgment to select the most appropriate level for partial foot amputation.

Determination of Amputation Level

A variety of tests have been put forward in the surgical and orthopaedic literature as the “best” method to determine the proper level of amputation. Most are based on correlating outcomes of preoperative tests with the ultimate healing of the amputated limb. These tests include arterial Doppler pressure measurements, fluorescein angiography, transcutaneous oxygen tension measurements, and xenon clearance.

Most of the studies on predictive tests for amputation healing levels have been aimed at assessing the segmental vascularity of the limb, that is, healing below the ankle, at the ankle, below the knee, or above the knee. They typically do not address the question of the proper level of partial amputation within the foot. For this reason, these tests are often difficult or impossible to apply to the decision-making process of foot salvage, which depends greatly on local wound factors of gangrene, infection, and general perfusion of the foot. Differences in vascularity between a transmetatarsal amputation and a Syme ankle disarticulation are at best difficult to determine based on noninvasive preoperative testing. Even when tests indicate differences, their reliability for differentiating levels of viability within the foot has not been clearly proved or widely accepted.

None of the tests has been demonstrated to have a clear superiority to forecast accurately amputation healing within the foot. Each of these procedures has clear advantages, and a few of these characteristics are mentioned here, although this is by no means an exhaustive review of this broad subject.

The most commonly used and widely available test is the arterial Doppler ultrasound arterial Doppler ultrasound . This test is most useful as a guide to the general level of perfusion of the foot and is the best initial screening test to determine whether the patient needs a vascular surgery consultation and an arteriogram. The Doppler ultrasound is painless, quick, and inexpensive and does not require extensive instrumentation. Pulse-volume recordings (waveforms) are reliable indicators of perfusion, but ratios of ankle pressures to arm pressures can be unreliable, especially in the diabetic patient with noncompliant, calcified vessels that give falsely elevated pressures. For healing of distal amputations, the most reliable measures are toe pressures. A forefoot amputation is likely to heal with a toe pressure of 40 mm Hg or greater. Distal wound healing in the presence of toe pressures between 30 and 40 mm Hg is possible but less predictable.

Other Factors Affecting Healing

Other factors that affect healing include edema in the local tissues, systemic disease, and nutritional factors. Systemic factors include glycemic control in diabetic patients or vasculitis in patients with inflammatory arthritides. The adequacy of nutritional status is critical to achieving healing. Simple indices of nutritional status such as albumin levels can have a predictive value for wound healing after amputation. Published measures of minimal acceptable levels for healing are the total lymphocyte count, which should be greater than 1500/µL; serum albumin 3.5 g/dL or greater; total protein 6.2 g/dL or higher; and hemoglobin greater than 11 g/dL.

Amputation of the Distal Toe and Nail

The terminal Syme amputation of the distal toe has been described as treatment for severe posttraumatic nail deformity, onychomycosis, or recurrent infection of the great toenail. This amputation can be used for similar problems in a lesser toe as well. A key technical element is to remove sufficient bone from the distal phalanx to allow wound closure without tension.

Amputation of the Great Toe