Amputations of the Foot

As a percent of amputations involving the lower extremity, those around the foot and ankle are becoming increasingly common ( Fig. 15.1 ). With advances in vascular and perfusion assessment and improvements in foot prostheses and footwear, success with ankle and partial foot amputations, as measured by functional, independent living, seems to be improving. When it is determined that limb salvage is not in a patient’s best interest, ablation by amputation or disarticulation should be viewed as a reconstructive procedure rather than a treatment failure.

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Levels of partial foot amputation.

Indications for distal lower extremity amputation include trauma, peripheral vascular disease, neuropathy, infection, and tumor. Surgeons must be aware of advances in knowledge, technique, and technology that may influence the decision for or against amputation. Over the past few years, more literature has emerged to better define indications for amputation. The Lower Extremity Assessment Project (LEAP) study suggests that injury severity scoring systems, including the Limb Salvage Index, Predictive Salvage Index, and Mangled Extremity Severity Score, are insensitive in indicating those patients who ultimately benefit from amputation. The LEAP study did, however, find the Mangled Extremity Severity Score highly specific in ruling out patients who do not require amputation.

Presently, diabetic patients comprise over 70% of amputations because of ischemia, and over 30% of diabetic patients with a partial foot amputation will ultimately progress to a more proximal level of limb loss. Research indicates patients with diabetes fear major amputation more than death. Therefore, compassion and education are critical components of treatment.

Current guidelines for diabetic foot infections recommend histological analysis and culture for a diagnosis of osteomyelitis. However, bone biopsy may not be as reliable as once thought. Severe postoperative infections have been found to be significantly more frequent in patients with complicated diabetes (defined as the presence of neuropathy, history of ulcers, Charcot neuroarthropathy, or vascular disease) than in those with uncomplicated diabetes or patients without diabetes. Despite the definitive nature of an amputation, diabetic patients with severe neuroarthropathy or ulceration perceive their quality of life as equal to that of those with lower extremity amputation. The roles of the certified pedorthist, orthotist, and prosthetist should not be undervalued in maximizing function and minimizing complications after amputations of the lower extremity.

Nutritional status and limb perfusion must be evaluated before surgery. With over one third of foot and ankle amputations in diabetic patients progressing to a higher level, it is important to optimize healing potential preoperatively. Critical values have been established to predict wound healing after amputation in the lower extremity. Indications of adequate perfusion include an ultrasound Doppler ankle-brachial index of more than 0.5, although this may be falsely elevated in patients with noncompressible vessels (Monckeberg sclerosis) and transcutaneous oxygen perfusion pressure on room air of more than 40 mm Hg. Toe pressures may be the most reliable noninvasive vascular measure, with 45 mm Hg or greater predictive of healing. The nutritional status of a patient also is crucial in wound healing after ablation procedures around the foot and ankle. A serum albumin value less than 3.5 g/dL and a total lymphocyte count less than 1500/mL have been shown to correlate with poor healing. A healing rate of 82% can be obtained with a total lymphocyte count of more than 1500/mL and an albumin level of at least 3.5 g/dL. Patients with poor nutritional status should be evaluated for dietary supplementation before surgery to maximize healing. Alternatively, a higher-level amputation may be chosen if delaying amputation carries an unacceptable risk to the patient. Gangrene upon admission and insulin-dependent diabetes are significant risk factors for reamputation.

Meticulous surgical technique, including avoidance of excessive pressure on the skin edges with forceps and use of thick skin flaps, may decrease wound complications. Refraining from tourniquet use, controlling hemostasis, and avoiding hematoma formation may be beneficial.

Expanding coverage options and advances in wound management have allowed greater success in more distal amputations. Advancement, rotation, transposition, and pedicle flaps are possible for limited coverage requirements around the foot and ankle; however, vascularized free flaps often are necessary for more extensive coverage. Consulting a plastic and reconstructive specialist early in treatment often is beneficial. There are many types of dressings, including hydrocolloid, hydrogel, alginate, and debriding agents, and other types of biological dressings, such as Allomatrix and Graftjacket regenerative tissue matrix (Wright Medical, Memphis, TN). Platelet-rich plasma gel application has shown promise for treating diabetic, dysvascular wounds, as have growth factor and biologic wound products. Negative-pressure wound (vacuum-assisted closure) dressings also may be beneficial in larger wounds of the midfoot, hindfoot, and ankle. The vacuum-assisted closure system has been shown to heal diabetic foot wounds proximal to the transmetatarsal level faster and more predictably than moist gauze dressing changes. Vacuum-assisted closure dressings may be of less benefit in small forefoot wounds and wounds with severe peripheral vascular disease. It has been suggested that gauze-dressing changes may be more efficacious for patients with peripheral vascular disease. Larger, condition-specific studies are needed to better determine the role of each of these treatment options. What is evident is the benefit of treatment by a multidisciplinary team willing to collaborate to help the patient.

Toe Amputations

Amputation of a single toe, with few exceptions, causes little disturbance in stance or gait. Amputation of the great toe does not functionally affect standing or walking at a normal pace. However, if the patient walks rapidly or runs, a limp appears because of the loss of push-off normally provided by the great toe. Amputation of the second toe frequently is followed by severe hallux valgus because the great toe tends to drift toward the third to fill the gap left by amputation. Smith recommended a second ray amputation and narrowing the foot. Screw fixation is used in this technique ( Fig. 15.2 ) to prevent a severe valgus deformity from occurring. Amputation of any of the other toes causes little disturbance. Toe amputations are the most common partial foot amputation and, of these, the fifth toe is most commonly amputated, the usual indication being overriding on the fourth toe. Here amputation often is preferred to reconstructive procedures because it is simple and definitive ( Fig. 15.3 ). Toe amputation is a significant predictor of future limb loss. Amputation of all toes causes little disturbance in ordinary slow walking but is disabling during a more rapid gait and when spring and resilience of the foot are required. It interferes with squatting and tiptoeing. Usually, amputation of all toes requires no prosthesis, other than a shoe filler ( Fig. 15.4 ). Amputation of more than two rays often is more disabling than a transmetatarsal amputation.

Amputation through the metatarsals is disabling in proportion to the level of amputation—the more proximal the level, the greater the disability. The loss of push-off in the absence of a positive fulcrum in the ball of the foot is chiefly responsible for impairment of gait. No prosthesis is required other than a shoe filler.

Foot amputations proximal to the transmetatarsal level result in considerable gait disturbance because of the loss of support and push-off. Such procedures occasionally are indicated, however, after severe trauma and in diabetic patients. Better preoperative tests for tissue perfusion have made it possible to predict with reasonable accuracy the patients in whom toe, ray, and partial foot amputations will heal. In addition to using the ankle-brachial index, toe pressures of greater than 45 mm Hg and transcutaneous partial pressure of oxygen of more than 37 mm Hg correlate with healing of wounds. A transcutaneous partial pressure of oxygen of less than 20 mm Hg indicates that healing is unlikely at that level.

Good healing and functional results may be expected in diabetic patients after open Lisfranc or Chopart amputations with secondary closure. However, amputation at either level often results in an equinus deformity, because of loss of the foot dorsiflexor attachments ( Fig. 15.5 ) and may require an ankle arthrodesis or revision to a higher level because such deformities prevent ambulation. Heel cord tenotomy or tenectomy can prevent early equinus deformities from becoming fixed, which can decrease the number of patients requiring revision to a higher level. Lisfranc ( Fig. 15.6 ) and Chopart amputations done for severe foot trauma have a higher failure rate. Patients who heal function well with simple prosthetic devices, and good results can be achieved with amputation levels that have been unsatisfactory in the past.

Terminal Syme Amputation

This amputation shares the name of the Syme amputation through the ankle because of the similar reconstruction of the plantar flap used for coverage. Indications include hallux terminal ulcerations, chronic ingrown nails with paronychia or nail deformity, hallux tuft osteomyelitis, or traumatic injury to the tip of the hallux involving the nail bed. Care must be taken to remove the entire matrix while attempting to maintain the insertion of the extensor and flexor hallucis longus.

Technique 15.1

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  Palpate the hallux interphalangeal joint and mark the dorsal incision just distal to this level in a transverse fashion. A digital tourniquet can be used but is usually not needed.

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  Extend the incision on both sides of the hallux nail bed to include the paronychia. Distally extend the incision to include the terminal aspect of the hallux ( Fig. 15.7A ).

  

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  Remove the nail plate, nail bed, contiguous soft tissue and distal aspect of the distal phalanx (retaining the extensor hallucis longus and flexor hallucis longus insertion) ( Fig. 15.7B ).

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  Close the skin in a single everted layer ( Fig. 15.7C ). Do not attempt to contour the skin tags because they will remodel over time ( Fig. 15.7D ) and removing them can lead to wound problems.

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  Dress the wound in a mildly compressive forefoot dressing.

Postoperative Care

A sterile dressing is kept in place for 2 weeks. The sutures are removed at 12 to 16 days. Weight bearing is allowed in a stiff-soled shoe until the wound is healed. Then the patient may transition to a shoe with a wide toe box.

Amputation at the Base of the Proximal Phalanx

Maintaining the base of the proximal phalanx often is preferable to metatarsophalangeal joint disarticulations. This allows for retention of some weight-bearing properties, especially in the hallux, where 1 cm of proximal phalanx allows for contribution by the flexor hallucis brevis and the plantar fascia. It also may slow the deviation of adjacent toes when one of the lesser digits is amputated ( Fig. 15.8 ).

Technique 15.2

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  The skin incision varies with the toe involved. For the great toe, make a long medial incision and then circumscribe the digit. Begin the incision over the first metatarsal head in the midline medially and curve it distally over the lateral and posterior aspects for a distance slightly greater than the anteroposterior diameter of the digit and slightly longer plantarly than dorsally ( Fig. 15.9A ).

  

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  With an oscillating saw, osteotomize the base of the first proximal phalanx 1 cm from the base. Ensure that the attachments of the flexor and extensor hallucis brevis are preserved ( Fig. 15.9B ).

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  In the second, third, and fourth toes, amputation is done through a short dorsal racquet-shaped incision ( Fig. 15.9C ). Begin the incision 1 cm proximal to the metatarsophalangeal joint and extend it distally to the base of the proximal phalanx, then curve it to pass around the toe across the plantar surface at the level of the flexor crease.

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  With an oscillating saw, osteotomize the proximal phalanx 1 cm from the base, ensuring the integrity of the flexor and extensor digitorum brevis.

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  In the fifth toe, fashion a lateral incision and extend it circumferentially around the medial aspect of the toe distally to the level of the proximal interphalangeal joint. Again leave 1 cm of bone at the base of the proximal phalanx.

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  Draw the extrinsic tendons distally, divide them, and allow them to retract.

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  Identify the digital nerves and divide them proximal to the end of the bone and divide and ligate the digital vessels.

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  In either the great toe or fifth toe, copiously irrigate the wound, obtain hemostasis, and close the wound by approximating the skin edges ( Fig. 15.9D ).

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  In amputation of the second, third, or fourth toe, close the skin edges with interrupted nonabsorbable sutures, as shown in Fig. 15.9E .

Postoperative Care

Protect the amputation site with a sterile dressing for 12 to 16 days. Remove the sutures in dysvascular patients at 21 to 23 days, unless the wound has obviously healed sooner. Protected weight bearing usually is not needed. A shoe with the toe box cut out or a wooden-soled postoperative shoe is worn until the sutures are removed. When the edema has subsided, ambulation in a supportive, soft-soled, accommodating shoe is allowed.

Metatarsophalangeal Joint Disarticulation

In the diabetic foot, ischemia or osteomyelitis or both are the most compelling indications for amputation at the metatarsophalangeal joint.

Technique 15.3

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  Fashion a long plantar and a short dorsal skin flap. Begin the incision at the level of intended bone section at the midpoint on the medial side of the toe and curve it over the dorsal aspect to end at a similar point on the lateral side. Fashion a similar plantar flap but make it slightly longer than the dorsoplantar diameter of the toe at the level of bone section.

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  Dissect the skin flaps proximally to the level of bone section.

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  Divide the flexor and extensor tendons and let them retract just proximal to the end of the bone.

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  Isolate and divide the digital nerves and ligate and divide the digital vessels.

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  Section the bone at the selected level and smooth its end with a rasp.

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  Close the flaps with interrupted nonabsorbable sutures.

Technique 15.4

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  Disarticulation of the metatarsophalangeal joint is carried out in the same manner as amputation through the base of the proximal phalanx, differing only in the level and manner of amputation of bone. The skin flaps may vary.

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  Continue the incision distally to the level of the metatarsophalangeal joint and extend it distally and circumferentially while proceeding plantarward ( Fig. 15.9C ).

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  Identify the capsule of the metatarsophalangeal joint and, with the toe in acute flexion, incise its dorsal side first; straighten the toe and expose and incise the remainder of the capsule after dividing the flexor tendons and neurovascular bundles, cauterizing the latter. Divide the neurovascular bundle distal to the bifurcation so as not to jeopardize the adjacent digits.

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  For the first and fifth digit, fashion the incision in the same manner as described in Technique 15.2. If the skin allows, a longer plantar flap is probably indicated ( Fig. 15.10 ).

  

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  When performing a metatarsophalangeal disarticulation of the hallux, removing the sesamoids in the insensate foot is recommended. Stay close to the periosteum over the sesamoids ( Fig. 15.11 ).

  

Postoperative Care

Postoperative care is the same as after Technique 15.2.

First Or Fifth Ray Amputation (Border Ray Amputation)

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