Subtotal Pedal Amputations

Abstract

Proper treatment for the compromised diabetic foot often requires surgical correction and subtotal pedal amputation. This article discusses various levels of amputation of the human foot, including digital, ray, transmetatarsal, midfoot, and Syme amputations. Surgical techniques and biomechanical considerations are presented in order to assist the surgeon in planning for the most functional outcome of the patient. A review of the literature and the experiences of the authors are presented.

Patients with diabetic complications severe enough to require an amputation usually have multisystem compromise. Such factors as cardiovascular disease, renal disease, peripheral vascular disease, neuropathy, impaired respiratory function, and poor nutritional status can present unique challenges to the surgeon who seeks an optimal outcome [1]. Diabetes mellitus affects 5% of the population in the United States, or nearly 16 million people. It is thought that in half of these people, the condition is undiagnosed [2]. The large number of lower-extremity complications (20% of all hospital admissions of people with diabetes are for lower-extremity infections) requires that many knowledgeable health-care providers work as a team to successfully manage the pedal complication. Fortunately, great advances in patient care have been made in recent decades, so the patient with diabetes can maintain a higher quality of life even if an amputation is required.

As discussed elsewhere in this issue, two of the major causes of foot problems in diabetic patients are neuropathy and arterial insufficiency [3]. Although different in their course of pathology, both can lead to the same devastating result—lower-extremity infection. If not treated aggressively and early, infection can lead to tissue necrosis, abscess formation, gangrene, and osteomyelitis [4]. Infection in a cutaneous diabetic ulcer can often spread to the contiguous osseous structures. Underlying osteomyelitis has been found to be present in 33% to 67% of diabetic patients with moderate-to-severe foot infections [5]. If the infection develops rapidly enough, or is neglected long enough, it will not be controllable by nonsurgical means. Emergency incision and drainage, including adequate debridement of necrotic tissue, is necessary to treat uncontrolled infections in the diabetic patient [6]. All purulence must be drained through surgical exploration of the infected fiscal compartments. Empiric antibiotic therapy should be initiated as soon as possible to stabilize the patient until definitive antibiotics can be administered.

Once the patient is stabilized, consideration must be given to the removal of nonviable tissue and modification of mechanically unsound weightbearing surfaces in order to preserve the ambulatory capacity of the patient. Often this requires carefully planned amputations. Amputation rates are higher in men [1], among racial and ethnic minorities [7], and in older people [8]. Unfortunately, previous amputations are a strong predictor of future amputations. Up to 20% of people with diabetes who undergo amputation return to the hospital for another amputation within 12 months. This percentage approaches 51% after 5 years [1].

Goals of Surgery

The object of an amputation is the removal of nonviable tissue while retaining the greatest amount of function possible [9]. Amputations in the foot or at the ankle level should normally be reserved for patients who can walk [10]. However, the ability of a patient to transfer to and from a wheelchair is very important to postamputation care, and the surgeon should take this into account when determining the best level for an amputation. The patient’s rehabilitation and wound-healing potential should be considered in determining the amputation level. The term “biologic amputation level” has been used to describe the most distal functional amputation level with reasonable (85% to 90%) potential to support wound healing, as determined by adequate vascular inflow, tissue nutrition, and immunocompetence [11]. When the biologic amputation level is within the foot, it is possible to perform an amputation that maintains limb length and muscle attachments for ambulation, thereby avoiding the additional physical exertion associated with using a limb prosthesis.

Preoperative Considerations

Prior to surgery, the general condition of the patient should be stabilized. However, patients with significant infections may need surgery to stabilize their medical condition. Diabetic patients who have sepsis, or in whom sepsis is strongly suspected, should have an immediate incision and drainage in an attempt to stabilize their medical condition. Patients with diabetes mellitus are at a higher risk for complications during surgical intervention as compared with the nondiabetic population. Additionally, they have increased perioperative morbidity and mortality [12].

Vascular status is critical in determining the healing potential of the patient. An ankle-brachial index of greater than 0.45 is correlated with healing [13]; however, the ratio may be falsely elevated in patients with calcified vessels. Other results of vascular studies that correlate with wound healing in diabetic patients are digital pressures of 40 to 50 mm Hg, or TcPO₂ values of at least 20 to 30 mm Hg [14]. If the patient is stable and the vascular examination shows low healing potential, a vascular surgeon should evaluate the patient to determine whether he or she is a candidate for vascular reconstruction. Other preoperative criteria to determine if nutritional intervention is needed prior to surgery include a serum protein level greater than 6.0 g/dL, a serum albumin level greater than 3.0 g/dL, and a total lymphocyte count greater than 1500/μL [15].

Although proper glucose control is an important part of any surgery in the diabetic patient, varying opinions exist as to the best method of achieving good control. Patients receiving amputations should take nothing by mouth beginning at midnight the night before surgery (or at least 6 hours before surgery, patient condition permitting). The patient should be given adequate fluids intravenously on the morning of surgery. Once this intravenous infusion is started, regular insulin, glucose, or both are administered as necessary to maintain a glucose level of between 100 and 200 mg/dL. An insulin drip should be considered for hard-to-manage patients. Following surgery, patients should be returned to their usual insulin regimen as quickly as possible. With the assistance of the hospital endocrinologist, insulin levels should be adjusted according to glucose readings made in the hours after the operation.

In patients with significant infections, empiric antibiotic therapy should be started immediately. A recent study (unpublished) at the authors’ institution demonstrated that even short delays (3 to 4 hours) in administering antibiotics lead to significant increases in morbidity (3- to 4-day increase in hospital stays). However, cultures obtained within 24 to 48 hours after the antibiotics are started appear to be unaffected by the antibiotics.

Surgical Technique

Surgical handling of skin and soft tissue must be meticulous. Skin viability ultimately determines the healing capacity of an amputation stump. Skin should be retracted gently, with care taken not to occlude small blood vessels during handling and closure. Diabetic skin can be devitalized by seemingly minimal crush injuries, and dissection between layers should be avoided to preserve circulation. Skin flap preservation and design is the most important aspect of an amputation. Flap planning should start when the patient is first taken to the operating room for incision and drainage. The incision for this procedure should be placed to best accommodate the possibility of a future amputation. All viable skin and soft tissue should be preserved at the time of the initial incision. It is much easier to design the final flaps after the bony resection is completed. If the flaps cannot be closed, the surgeon should consider resection of more bony tissue, skin grafts, or closure by secondary intention.

The use of tourniquets during surgery on diabetic patients is discouraged for several reasons. First, the intraoperative assessment of bleeding is a useful guideline for the viability of the flaps and can help determine the best way to modify them for optimal healing potential [16]. Additionally, tourniquets may occlude distal arterial bypasses or dislodge arterial plaques. Finally, the prolonged anoxia may reduce the viability of the flaps. If a tourniquet is used, it must be released prior to closing of the wound so that all bleeders may be ligated or coagulated to avoid a hematoma, which is another significant cause of flap loss.

The underlying soft tissue at the amputation site should be sharply resected. Nerves should be sectioned under traction so as to migrate proximally away from the incision site during closure. This prevents neuroma formation over bony prominences and areas of increased pressure. Tendons crossing the amputation site should be reattached to preserve their function at the ankle and rearfoot level. However, in cases with an active infection, the tendons should be retracted and cut proximally. Bone cuts should be made with a power saw to avoid fracturing the remaining cortices. Bone ends are rounded with a rasp or bur. Excessive bony prominences can result in poor healing and may lead to additional surgery to revise the amputation.

Preferably, the surgeon should close the incision with a nonabsorbable monofilament suture, using an interrupted technique, without causing tension or blanching of the skin. Skin staples may also be used. Large retention sutures, rather than deep sutures, should be used for closing dead space. Drains should be used in all cases where primary closure is performed. Suction-type drains should be used when possible. When the patient has an active infection, the wound should be packed open until it has resolved. When the wound is left open, all viable soft tissue should be preserved and the flaps should be loosely approximated with one or two large sutures. Packing should be loose. The use of antibiotic beads has not been shown to improve healing rates. However, this may relate to the selection of antibiotics; a study carried out in rabbits suggested that clindamycin should be substituted for gentamicin [17]. This technique for leaving the wound open minimizes the trauma to the flap, thereby maximizing the success rate. Delayed closure should be carried out as soon as reasonably possible.

Digital Amputations

Amputation of the hallux and lesser digits is reserved for cases involving localized gangrene and osteomyelitis in the phalanges. It has been reported that infection, gangrene, and osteomyelitis most commonly occur in the digits of the ischemic or neuropathic diabetic foot [18]. This procedure is commonly performed under regional ankle block with intravenous sedation, although spinal or epidural anesthesia may be acceptable if the patient’s overall condition requires it. All necrotic tissue should be removed, with adequate healthy skin flaps preserved for secondary wound closure. In patients with poor blood flow, the success rate for both lesser-digital and hallux amputation ultimately depends on successful limb revascularization [19].

The effects of digital amputation on weightbearing differ for lesser-digital amputation and hallux amputation. Generally, lesser-digital amputations have no significant effect on weightbearing. However, this is not the case with hallux amputations. Following hallux amputations, peak pressures on the sole of the foot are greater under the first metatarsal head, lesser metatarsal heads, and toes [20]. Quebedeaux et al [21] compared the deformities and ulcerations of feet in which the hallux was amputated with those of the intact contralateral foot. They concluded that hallux amputation contributes not only to ipsilateral deformities of the second and third digits, but also to new ulcer formation in patients with diabetes. Thus careful follow-up and properly fitted shoes are essential in treating these patients.

The occurrence of ulcer formation and subsequent osteomyelitis on the distal tuft of an elongated second digit is frequently seen in the diabetic foot. Because the second digit serves as a buttress to the hallux, amputation of this digit usually results in hallux valgus [22]. Once the infected second digit is removed, the clinician must ensure that adequate space-filling shoes are fabricated to slow the abductory migration of the hallux. Lesser-digital amputations also cause a worsening of hammer toe deformities in adjacent digits as a result of a progressive over-pull on the remaining tendon slips of the long flexor and extensor muscles.

Ray Resections

Ray amputation is indicated when the necrotizing or infective process requires resection of the digit and most, if not all, of the corresponding metatarsal. In the authors’ experience, fifth-ray amputations are most likely to be successful in the long term. A high enough percentage of first-ray amputations hold up over time to warrant trying them, particularly in compliant patients. However, central-ray resections tend to fail a high percentage of the time and should be reserved for patients who are sedentary or who refuse a transmetatarsal amputation. Resection of multiple rays leaves a narrow remnant of tissue that not only lacks sufficient surface area for ambulation but is difficult to accommodate even with custom-made shoes. Because removal of a metatarsal alters the weightbearing capacity of the foot, transfer lesions resulting in ulceration at adjacent metatarsal heads are a major long-term complication of ray resection [23]. When multiple rays or the central rays are involved, a carefully planned transmetatarsal or Lisfranc amputation has better functional results [24].

A ray resection generally involves a dorsal incision starting at the shaft of the metatarsal and extending distally until it diverges at the proximal interphalangeal joint; a “racquet-type” incision is used. In patients with osteomyelitis and a plantar ulcer, consideration should be given to a plantar incision that eclipses the ulcer in order to primarily close the wound. If performing a partial ray resection, the surgeon should transect the metatarsal with approximately a 45° plantar bevel and round the stump. Once the necrotic or infected tissue is removed, a thorough examination for pocket abscesses should be performed. Squeezing the foot from the area proximal to the amputation site and “milking” the wound distally might open up hidden abscesses that will express more purulence. Any signs of infection coursing proximally up the foot, especially along the tendon sheath, require a proximal extension of the incision so that all purulent material may be drained. After any additional debridement, copious amounts of saline flush are used at the site. If the deep plantar space is involved, a plantar incision may be necessary either in addition to or in place of the dorsal incision.

The amputation site is then packed open with sterile gauze and reexamined every 24 hours for clinical signs of infection and drainage. Wet-to-moist saline or hydrogel dressings are applied twice a day. Delayed primary closure approximately 5 to 7 days postoperatively if clinical and laboratory signs of infection are absent is preferable to healing by secondary intention. When the amputation is performed to close a noninfected wound, primary closure with nonabsorbable monofilament suture over a suction-type drain is indicated.

Transmetatarsal Amputation

The transmetatarsal amputation is an excellent option when osteomyelitis or tissue necrosis involves more than one digit or metatarsal in the forefoot. Unlike ray resections, transmetatarsal amputations also preserve the metatarsal parabola for a broader distribution of weight during ambulation. The primary deformity that occurs postoperatively is an equinovarus. The probability of an equinovarus can be reduced by preservation of as much metatarsal length as possible. Release or lengthening of the tendo Achillis should particularly be performed in patients who have even a mild equinus deformity. This procedure should be performed at the time of the amputation in noninfected cases and at the time of delayed primary closure in infected cases. A split anterior tendon transfer should be considered when a varus deformity is present or when the peroneus brevis insertion is compromised.

As with all amputations, consideration must be given to functional capacity and postoperative breakdown of skin, especially in the first 3 months after surgery [25]. Transmetatarsal amputation reportedly preserves foot function, is cosmetically acceptable, and does not require a prosthesis [26]. However, Mueller and Strube [27] studied functional mobility in six types of footwear among 30 diabetic patients who had undergone a transmetatarsal amputation. They found that physical performance and walking speed increased when these patients were wearing the combination of full-length custom-made shoes, a total-contact insert, and a rigid rocker-bottom sole, as opposed to regular shoes with a toe filler.

Hosch et al [28] studied the long-term outcome of successful transmetatarsal amputations. They obtained data from 35 diabetic patients receiving a transmetatarsal amputation and followed them for a mean of 15.1 months. They found that patients with a diagnosis of infection without underlying critical ischemia were significantly more likely to heal at the level of the foot following a transmetatarsal amputation. Patients who went on to undergo a higher-level amputation were also less likely to have had depth-inlay shoes prescribed.

The procedure for a transmetatarsal amputation consists of a dorsal incision directly to bone as far distal as possible. The incision is continued plantarly in the distal aspect of the sulcus, or just proximal to any necrotic plantar tissue, in an attempt to preserve the classic long plantar flap. The incision should be distal to any isolated plantar ulcers. The ulcer should be eclipsed and closed in a linear fashion to preserve the flap length. This not only permits the thick plantar skin and subcutaneous fat to be present during weightbearing, but also allows for proper trimming during closure. Vessels are ligated and nerves and tendons are resected as far proximally as possible. The metatarsals are best divided in a parabolic manner with the use of a power saw. Care should be taken to bevel the metatarsal ends and round off sharp edges. The first and fifth metatarsals are beveled medially and laterally to prevent focal points of pressure. All of the metatarsals should be rounded plantarly. Irrigation is performed and a drain or a suction apparatus is placed at the osseous level before flap closure. Large horizontal mattress 0 sutures are used to approximate the skin flaps before closing with simple, interrupted 4-0 sutures or skin staples. Absorbable suture and buried sutures should be avoided to minimize the possibility of a suture reaction’s being mistaken for an infection. Care should be taken to prevent tension at the wound edge. Delayed primary closure should be used in infected cases. However, the plantar flap should be loosely approximated with the use of one or two retention sutures with loose wound packing to minimize the likelihood of flap loss in cases where a delayed closure is planned.

Midfoot Amputations

Midfoot amputations in the tarsometatarsal joint (Lisfranc’s amputation) or midtarsal joint (Chopart’s amputation) are indicated when forefoot necrosis and gangrene extend proximally enough to preclude closure of a transmetatarsal amputation, but not so proximally as to warrant a Syme or below-the-knee amputation [29]. The major complication following this procedure is postoperative equinus or equinovarus deformity encountered in midfoot amputees [30]. This is due to the resection of the tendons that dorsiflex the foot, thus allowing unopposed pull of the heel cord and subsequent ankle equinus. Likewise, over-pull by the anterior tibial tendon can result in varus deformity. To combat these deformities, the procedure today is commonly modified to include an Achilles tendon lengthening or tendon transfer of tibialis anterior to maintain the foot at 90° [31]. The advantages of midfoot amputations include the preservation of normal limb length and the availability of a large, well-padded weightbearing surface at the stump end.

Lisfranc’s Amputation

In a Lisfranc amputation, as with a transmetatarsal amputation, an attempt is made to produce a long plantar flap and a short dorsal flap. The incision is made in the same manner as for the transmetatarsal amputation, with linear incisions on the medial aspect of the first ray and lateral aspect of the fifth ray. These flaps should be modified at the time of closure or delayed closure, thereby minimizing the possibility of removing too much skin. Disarticulation occurs at the first metatarsocuneiform joint. The base of the second metatarsal is resected with a power saw distally in the same plane as the first and third cuneiforms. This not only preserves the “keystone” effect of the second metatarsal base but allows for a smooth surface at closure. The second metatarsal should be disarticulated in cases where second metatarsal osteomyelitis is present. The third and fourth metatarsals are disarticulated at the joint. If possible, the fifth metatarsal is resected with a power saw just distal to the base. This is done to preserve the attachment of peroneus brevis at the base of the fifth metatarsal [26]. After copious irrigation, closure is performed in the same manner as in the transmetatarsal amputation with no tension on the skin flaps.

Chopart’s Amputation

In a Chopart amputation, the initial incision courses dorsally and distally to the talonavicular and calcaneocuboid joints by starting at the navicular tuberosity and ending midway between the lateral malleolus and the base of the fifth metatarsal. The incision continues distally adjacent to the first and fifth metatarsals before connecting plantarly at the heads of the metatarsals. Once the plantar flap is dissected, the ligaments of the talonavicular and calcaneocuboid joints are divided. An important technical consideration in this procedure is the transfer of the tibialis anterior tendon to the talus for attachment. This tendon can be firmly attached to the neck of the talus by using a drill hole. An Achilles tendon lengthening or release should also be used. An open Chopart amputation without flap preservation or tendon work is useful for life-threatening foot infections. This procedure can subsequently be converted to a Syme amputation.

Syme’s Amputation

The Syme amputation [32] is indicated in diabetic patients with either extensive forefoot gangrene or ulceration too advanced for any of the previously discussed amputations. This procedure involves disarticulation of the ankle, while maintaining the fibroadipose weightbearing tissue of the heel pad for protection of the end of the distal tibia. Amputation at the Syme level helps maintain the patient’s independence and decreases the rehabilitation expense associated with more proximal amputation [33]. However, owing to the systemic nature of diabetes and its common manifestations of neuropathy and vascular insufficiency, concerns still exist about wound healing and residual limb problems.

In an attempt to reduce the risks of inadequate wound healing, Wagner et al [34] listed the following contraindications for Syme amputations: absent femoral pulses, elevated urea nitrogen, gangrene or purulence at the heel, resting pain, or abrupt temperature change between the knee and ankle. A palpable posterior tibial pulse increases the chance of successful outcome. After observing that 19 of 22 patients with a palpable posterior tibial pulse achieved primary healing, Francis et al [35] reduced the contraindications of Wagner et al to only the absence of a posterior tibial artery pulse. Additionally, Laughlin and Chambers36]. found that 90% of severely diabetic patients with triphasic Doppler wave forms or palpable posterior tibial artery pulses and 57% of patients with a monophasic posterior tibial artery wave form achieved a healed wound suitable for prosthetic wear.

The Syme amputation is the most difficult and technically challenging procedure described in this article. In the presence of gross infection and sinuses, the procedure can be divided into two segments 6 to 8 weeks apart [37,38]. The first segment involves the preservation of the plantar heel flap and posterior tibial artery. With the foot at 90°, an incision is made plantarly and 45° dorsally from a point 2 cm below the medial malleolus and 1 cm below the lateral malleolus. The talus and calcaneus are exposed. The talus is sharply dissected from the ankle mortise, with care taken to preserve the posterior tibial artery. The Achilles tendon is carefully divided to allow removal of the calcaneus. Extraction of the calcaneus involves tedious subperiosteal dissection to preserve the anatomical and physiologic structure of the heel pad. Copious irrigation is performed in the area before closing the flap loosely with retention sutures and drainage placement.

Once infection has cleared, the second stage of the Syme amputation is performed. This consists of osteotomy of the malleoli. The subchondral portion of the distal tibia is also removed so that the weightbearing surface is parallel to the ground during stance. Following copious irrigation, the plantar skin flap is sutured to the anterior incision across the ankle. It is critical to place the plantar fat pad directly beneath the tibial osteotomy. Failure to do so could result in shifting and displacement of the plantar fat pad during ambulation, leading to a total loss of the shock-absorptive qualities of this tissue [39]. The patient remains nonweightbearing for approximately 4 weeks. Owing to the shortening of the leg, the use of a full prosthesis is necessary. A suboptimal stump can often be compensated for by a good prosthesis in which load transference occurs at the proximal tibial level, thus preventing full weightbearing on the stump in the socket [40]. The authors recommend that the heel pad be sutured to the tibia posteriorly and anteriorly in order to minimize fat-pad migration.

The one-stage Syme amputation basically eliminates the waiting period before the malleoli and distal tibia are osteotomized and flap closure is performed. Pinzur et al [41] studied the differences between the one-stage and the two-stage Syme amputations in 44 diabetic adults with nonsalvageable feet as a result of infection. They concluded that in properly selected diabetic patients, the Syme amputation may be performed as safely in one stage as in two stages. Additionally, a separate retrospective review by the same authors found that of the 31 patients whose two-stage Syme amputations eventually healed, none required subsequent revisions during 5 years of follow-up [42]. However, for the successful outcome of this procedure, the importance of education about residual limb care and frequent inspection cannot be overemphasized.

Summary

Tissue loss, deep infection, osteomyelitis, and chronic ulceration are some of the most frequent reasons for amputations in patients with diabetes [43]. Amputation in the diabetic patient should not be viewed as treatment failure, but rather as a reconstructive process that combines the most distal biologic level with the greatest functional capacity of the lower extremity. Knowledgeable perioperative management and proper surgical technique are essential for increasing the chances of a successful outcome in diabetic patients. Digital, ray, transmetatarsal, midfoot, and Syme amputations are useful interventions to preserve the functional capabilities of these patients. However, the long-term success of these procedures depends on proper use of custom-molded shoes, prostheses, physical therapy, and a continuous foot- care program.