The common factors indicating amputation of a part of the body are trauma, interference with the vascular supply, malignant neoplasm, chronic osteomyelitis, life-threatening infections, inoperable congenital limb deformity in children, the need to increase function, and, occasionally, the cosmetic effect.
In the presence of trauma, it is first necessary to evaluate carefully the extent of tissue and vascular damage in terms of possibly salvaging the extremity. With the recent advances in peripheral vascular repair and grafting, reestablishment of distal blood flow following arterial injury, blockage by arteriosclerosis, or embolus is often possible. It is essential to combat shock with intravenous administration of fluids and colloid solutions until the patient's general condition is improved sufficiently to withstand the operation. With diabetes or advanced vascular disease, the usual strict medical measures are taken to regulate these associated diseases. If there is localized skin infection at the proposed level for amputation, the procedure is delayed whenever possible. In the presence of wet gangrene, packing the leg in ice or dry ice combined with the application of a tourniquet just below the site of proposed amputation not only may lessen toxicity but also may decrease the incidence of wound infection, since the lymphatics may be cleared before amputation. The threat of gas gangrene may be a real one when the arterial supply to the extremity has been severely compromised, either by intra-arterial occlusion or trauma with inadequate debridement and a closed space infection.
Spinal anesthesia is commonly used for major amputation of the lower extremities, inhalation anesthesia for major amputations of the upper extremities, and plexus block or local infiltration anesthesia for amputation of the fingers and toes.
(See Plate 231.) In amputations of the upper extremity, the patient is placed near the edge of the table with the arm extended and abducted to the desired position. For amputations of the lower extremity, the leg may be elevated with several sterile towels under the calf.
In the absence of infection, the extremity is elevated to encourage venous drainage before a tourniquet is applied. The tourniquet is placed above the knee for amputations of the lower leg and foot, high in the thigh for amputations of the knee and lower thigh, and above the elbow to control the brachial artery for major amputations of the forearm. In cases of arteriosclerosis, the tourniquet should not be used because of the possibility of damaging the blood supply to the stump. Sterile elastic bands may be applied to the base of the digit for minor amputations. The skin is prepared with the usual antiseptic solutions well above and below the proposed site of amputation. In major amputations, the entire extremity may be wrapped in sterile adherent plastic drapes to enable the assistant to hold it and change its position as desired.
The efficiency of modern prosthesis has eliminated the time-honored “sites of election.” Generally, the pathology dictates the site of amputation, with the goal of preserving all possible length. This is particularly true of the upper extremity.
The rule of saving all possible length does not apply necessarily to the lower extremity. However, whenever possible, the knee should be saved, since it provides major functional advantages. Although the blood supply to the upper extremity is usually adequate, the reverse is often true for the lower extremity. Furthermore, the problems of weight bearing and retaining adequate soft tissue to cover the stump affect the site of election of the lower extremity, since an inadequate blood supply, often after failure of a vascular bypass graft, is the most common indication for amputating the lower extremity.
Since the profunda femoral artery tends to be the main channel after occlusion of the superficial femoral vessels or a femoral-popliteal bypass graft, the site of amputation must be selected well within the zone adequately supplied by the vessel. Accordingly, the amputation is usually above the knee. For this reason the supracondylar amputation (Figure 1, A) continues to be the most frequent site for amputation in the presence of arterial insufficiency, although a below-knee one is preferred if possible. It can be technically performed in a short time with the best assurance of primary healing of the flaps. Knee disarticulation (C) and transcondylar amputation (B) yield an enlarged, rounded end that is cumbersome and difficult to fit with a prosthesis.
The rule of saving all possible length does not apply to below-knee amputation. Long leg stumps are not recommended because of their poor tolerance of prostheses. Since the anterior margin of the tibia is usually beveled, there must be enough solid tissue with good blood supply to cover it, as provided by a longer posterior flap. A short below-knee stump is preferable to knee disarticulation. A below-knee amputation longer than 20 cm is probably not any more functionally effective, and poor circulation may interfere with healing. A very short fibula tends to migrate laterally and may be removed in a short below-knee stump. In a longer stump, a little bone graft between the fibula and the tibia prevents migration.
Although ankle amputations have few indications, chiefly trauma, the Syme amputation lends itself to a very serviceable end-weight-bearing prosthesis, but it has cosmetic disadvantages in females (Figure 1, D). There is general agreement that a most satisfactory foot amputation is the transmetatarsal. In the presence of vascular insufficiency to the lower extremity, amputations about the ankle or foot should be performed cautiously for secure indications, especially in the presence of infection, because they frequently heal poorly, necessitating secondary procedures.
Formerly, the junction of the lower and middle thirds of the forearm was considered the optimum site for amputations; however, newer artificial limbs that include pronation and supination movements make it desirable to save all possible length (Figure 4). Length is again important in the hand, where a partial amputation of the fingers or of all fingers, leaving an opposing surface at the thumb for gripping, allows better function than can be provided by any prosthesis. A stump of any length in the forearm will give better function than an amputation above the elbow, and it eliminates an elbow hinge in a prosthesis.
As a general rule it is desirable to have the scar in the posterior of the stump in the upper extremity, since the prosthesis bears largely on the distal surfaces of the stump. The scar for end-bearing stumps of the lower extremity should preferably be posterior to the end of the stump. In minor amputations of the fingers and toes, long palmar and plantar flaps are made to cover the stump with a thick, protective pad of tissue (Figures 2 and 5). Racket incisions are advisable for amputations of the toes, since they may be extended upward to permit exposure of the metatarsals (Figure 3), or they may be used for amputations of digits where all possible length must be preserved. This is especially true for injuries of the thumb (Incisions B, C, and D, Figure 6). Racket incisions with removal of the head of the metacarpal or metatarsal give a good appearance to the extremity but considerably diminish the breadth of the foot or palm.
Sufficient soft tissue must be present to approximate easily over the end of the bone, but excessive amounts are avoided, since bulky soft tissue hinders the fitting of a prosthesis. Arteries and veins should be tied individually. Nerves are divided at as high a level as possible. Two Kocher clamps are placed on large nerves 0.5 cm apart before division of the nerve. The nerve then is severed sharply just beyond the distal clamp, and the nerve is doubly ligated with 00 nonabsorbable suture just distal to the clamps. All cut nerves develop neuromas; therefore, placement of the cut end of the nerve is important. It should be remote from scar and away from areas of pressure, since the neuroma becomes symptomatic when pressure is applied.
The bone should be divided at a sufficiently high level to permit the soft parts to approximate, producing a thick covering for its end. The sharp margins of bone are beveled either with a rongeur or rasp.
All bleeding points are tied carefully so that, in the ordinary case, drainage is unnecessary. The investing fascia rather than the deep muscles is loosely approximated with interrupted nonabsorbable sutures. When there has been considerable oozing or a moderate amount of infection distal to the site of amputation, through-and-through drainage may be instituted. If a guillotine type of amputation was carried out in the presence of a progressing infection, the wound is left open to be closed secondarily later, or the extremity is reamputated later at a higher lever to permit primary closure.