Chapter 16A - Atlas of Limb Prosthetics: Surgical, Prosthetic, and Rehabilitation Principles
Partial-Foot Amputations: Surgical Procedures
F. William Wagner, Jr., M.D.
Vascular disease and trauma are the major causes of lower-limb amputation. Atherosclerosis with or without diabetes mellitus accounts for nearly 80% of the problems severe enough to require amputation. Congenital and acquired deformities, neoplasms, and infections account for fewer cases. Trauma from industrial, motor vehicle, and sporting activities has increased in incidence and severity. The treatment of neoplasms has undergone marked changes. Amputations should be performed by surgeons familiar with staging techniques, perfusion techniques, local resection, and endoprosthetic replacements. The casual surgeon should not embark upon the care of a patient with malignancy of the lower limbs.
The ultimate surgical treatment for traumatic amputation is replantation of the severed part. It is now just over a quarter of a century since a successful replantation of an arm was performed. Several hundred major limb replantations have been performed at the Sixth Peoples Hospital in Shanghai, China. Many replacement teams have been formed in the United States. The most suitable levels for replantation are in the distal levels of both the upper and lower limbs. Microvascular techniques are used below the ankle and standard vascular techniques above the ankle. These procedures are appropriate only for the trained surgical team in a replantation center. Before transfer of any patient and the severed part, the center must be called for instructions on handling of the residual limb and the severed part.
Prevention of major amputation in patients with diabetic foot problems has aided in increasing quality of life. Multispecialty clinics and the "team approach" are proving superior.
Prediction of healing is the most important part of level selection. Experience in the treatment of such problems aids in providing an "experienced hand and eye" to give information beyond that obtained from vascular and other laboratory tests. The history, clinical course, and physical examination provide a wealth of information. Hair growth, nail growth, skin turgor and appearance, skin temperature with differences from level to level and from side to side, palpation of pulses, rapidity of onset of the problem, temperature curves, white blood cell response, and response to antibiotic treatment all aid in evaluation of the patient's problem.
As a general rule, all length possible should be saved. However, function of midfoot amputations is such that it is wise to shorten long uncovered metatarsals in order to obtain sufficient plantar skin coverage. Split-thickness skin grafts do not do well when applied to weight-bearing surfaces of the foot.
With newer techniques of microvascular transfer of innervated flaps, it is possible to salvage a foot that would have required a higher amputation (Fig 16A-1.). A severe fracture/dislocation with skin, bone, and muscle loss would have required a transtibial amputation (Fig 16A-2.). Debriding of the wound, external skeletal fixation, latissimus dorsi muscle transfers, and split-thickness skin grafts allowed full salvage and function (Fig 16A-3. and Fig 16A-4.). Thus, a vascularized and innervated flap has saved a weight-bearing foot in an area where an amputation would have been performed. In grade MB open fractures of the tibia and fibula, there may be a marked loss of soft tissues with a deficiency of tissue envelope, necrotic or absent bone, soft-tissue infection, but still a viable foot. A transtibial amputation is indicated, but will be quite short.
Length can be preserved through the use of a neurovascular island fillet from the foot, which will then be transferred to the end of the tibia and fibula to provide a transtibial amputation of sufficient length. Thus, saving all tissue possible from the injured foot can result in a more functional amputation. With few exceptions, the most functional residual foot is at the trans-metatarsal level or lower.
Loss of the toes, either partial or complete, will lead to relatively little disability that usually can be compensated for with simple shoe corrections. Sole stiffeners, rocker bottoms, and toe fillers aid in the restoration of function of short transmetatarsal, Lisfranc, and Chopart levels. Occasionally, a heel cord lengthening is needed to reduce distal pressures. Transfer of the everters and dorsiflexors may aid in balancing the residual foot.
Level selection in dysvascular patients has frequently been difficult. Oscillometry, plethysmography, ergo-metry, fluorescein tests, histamine wheal, radionuclide washout, laser Doppler, Doppler ultrasound, angiography, and similar tests have all been described as aids in evaluating the arterial blood flow. However, with all of these tests, clinical judgment still remains the most important part of level selection. In addition to the tests mentioned, an intraoperative test appears to have value in predicting healing. Appearance of bleeding at the skin level after release of the thigh tourniquet has been timed. When the most distal skin bleeds within 3 minutes after release of the tourniquet, there is an 80% to 85% chance for successful healing of the amputation incision. If bleeding is prolonged beyond 3 minutes, the next higher level should be tested. The tourniquet is not used if there has been previous vascular surgical procedures in the limb. Amputation is performed where healing is indicated by vascular analysis, adequate function is predicted, and the experience and skills of the operating surgeon are adequate for the procedure proposed.
TRANSCUTANEOUS DOPPLER ULTRASOUND
This instrument provides a sensitive stethoscope or flow detector that is able to measure the pulse when it cannot be palpated or heard with an ordinary stethoscope and can be used for determining blood pressure at that point (Fig 16A-5.). For this purpose, the instrument does not need to be directional, and several relatively inexpensive portable machines are available. A unit with an audible response is valuable in allowing the patient, family, and doctor to hear the difference between the diseased vessels and a normal one. The smaller the vessel to be measured, the higher the frequency of the signal. Frequencies of 9 to 10 MHz are recommended for the foot and toes. As recommended by the American Heart Association, the cuff width should be 120% of the diameter of the limb at the level being measured. Thus, four different-sized cuffs are usual for a satisfactory complete examination of the lower limb. The major vascular tree can be mapped with the instrument and areas of lessened flow and zero flow determined and marked on a chart (Fig 16A-6.). Collateral circulation is also mapped. Pulsation of the flow can be determined. Systolic pressures are measured from the groin to the toes at various levels. An ischemic index is calculated for each level by dividing the systolic pressure measured in the limb by the brachial artery pressure. For example, the systolic pressure may be 120 mm at the arm and at the thigh, 90 mm at the calf, 60 mm at the ankle, and 20 mm at midfoot. The ischemic index would be 1 at the arm and thigh, 0.75 at the calf, 0.50 at the ankle, and 0.17 at the midfoot. In this case, an ankle disarticulation is indicated if the skin of the heel is intact.
A triphasic full pulse is one similar to that heard at the brachial artery. A variation can be heard that is represented by the dicrotic notch. This indicates a virtually normal flow. A drop of 30 mm of pressure from one level to the next lower indicates a very definite decrease in circulation. When the flow becomes markedly decreased, a wind tunnel effect is heard with marked broadening of the width of the wave (Fig 16A-6.).. If there is a virtual block, there may be just background noise and various indications of nonpulsatile flow or complete silence. If there is a sudden acute blockage just below a relatively normal flow, there will be increasing sharpness of the sound until a "water hammer" effect will be heard just before the blockage. Immediately afterward, there will be silence until collateral flow begins to come into the distal vessel. With relatively little experience, a very complete vascular examination can be performed at the bedside with a portable transcutaneous Doppler ultrasound flowmeter.
If the ischemic index is insufficient for local healing at a functional level, a consultation is obtained from the vascular surgery service. Successful revascularization procedures such as endarterectomy, balloon dilatation, or bypass procedures can aid in local healing of the lesion, can allow local surgical procedures to be performed, or may allow amputation to be performed at a low enough level to save the knee (Table 16A-1.).
The ankle brachial index has been criticized for not predicting healing in transmetatarsal amputation. The index is to be measured at the proposed level of surgery. There can be a drop of pressure from the ankle to the midfoot that would be sufficient to preclude healing at the midfoot level. Nutritional status has also been noted to be an important predictor of healing. It must be again emphasized that all factors should be taken into consideration when determining amputation level.
All types of anesthesia may be used. Individual selection is made from preference of the patient, coexisting medical problems, and preferences of the anesthesiologist and surgeon. Intravenous regional anesthesia with a two-level tourniquet is excellent and appears to interfere least with the patient's general condition. A contraindication to the use of the tourniquet would be recent vascular surgery. Regional anesthesia with perineural infiltration of the posterior tibial, superficial peroneal, and sural nerves can be reinforced with small amounts about the peri-incisional areas. Several thousand thiopental (Pentothal) induction and inhalation anesthetics have been administered at Rancho Los Amigos Medical Center for diabetic and dysvascular patients with no intraoperative deaths for foot procedures. Hospital mortality has been less than 1% in the ankle disarticulation and foot amputation levels.
OPEN VS. CLOSED TECHNIQUES
All open wounds are eventually infected or colonized even with nonpathogenic bacteria. A paradox is thus created in leaving an amputation open when performed for severe infection. There is evidence in the literature that closed incisions do better than open incisions.These, of course, may be done with secondary closures, as indicated. Removal of the major amount of infected or gangrenous tissue by amputation usually leaves a number of bacteria behind in the surrounding cellulitis and lymphangitis. These usually can be controlled by the body's own defense mechanisms with the aid of appropriate antibiotics. Kritter has developed a technique for irrigating wounds of this sort with closure. His technique has virtually done away with open amputations in foot patients at Rancho Los Amigos Medical Center. A small plastic catheter is drawn into the wound through a separate stab incision (see Fig 16A-11.). The wound is closed relatively loosely and slowly irrigated with an appropriate antibiotic solution for 72 to 96 hours. The fluid dilutes the hematoma and aids in the removal of blood clots and debris between the sutures. Care must be taken with nephrotoxic and ototoxic antibiotics so that total amounts given do not exceed allowable limits. In a recent personal communication, Kritter states that he is now irrigating the wounds of similar patients without antibiotics and believes that the irrigating effect is the more important.
Many traumatic foot wounds and most diabetic ulcers are infected. Cultures and sensi-tivity studies are virtually mandatory in selection of the proper antibiotics. Inclusion of the infectious disease consultant as a member of the team has aided greatly in the care of these difficult patients.
SPECIFIC SURGICAL TECHNIQUES
This method of amputation has had a resurgence as a preliminary procedure to remove a severely infected part of the foot. In some cases sepsis can be controlled by amputation or leg drainage to be followed by a definitive procedure. Guillotine amputation as the primary operation is now archaic because the residual limb has a scarred closure that is rarely suitable for use of a prosthesis.
The toes can be excised from the tip to the base through any type of incision, provided that the flaps have an adequate base to support the length. The flaps must close without tension. They may be side to side, long dorsal flaps, long plantar flaps, fish mouth flaps, or any combination. With the great toe, it is desirable to keep enough of the base of the proximal phalanx to preserve the attachment of the short flexor and extensor tendons. This has been well borne out in a recent article on great toes amputated for replacement of thumb loss. The mobile pad appears to offer marked protection to the skin under the first metatarsal head (Fig 16A-7.). In the lesser toes, this does not seem to be as important, except in the fifth toe.
If sufficient viable skin is not present to allow a partial-toe amputation, a disarticulation at the metatarsophalangeal joint is quite satisfactory. Metatarsal head pressure can become more prominent, and fixation of the long extensor tendon to the dorsal joint capsule aids in elevation of the metatarsal head. A long plantar flap provides more durable skin coverage. Articular cartilage is resistant to infection and need not be arbitrarily removed. Stiffening, thickening and rockering of the shoe aids in restoring function of the great toe.
Metatarsal Ray Resection
Third-, fourth-, and fifth-metatarsal ray resections have been quite successful and leave a functional partial foot. With the use of the ischemic index obtained by transcutaneous Doppler ultrasound, the success rate has improved markedly. Complete removal of infected and necrotic tissue is important. Enough bone must be removed so that flaps may be closed without tension. For a single second, third, or fourth toe and ray, a V-shaped wedge is removed. This closes well and leaves a symmetrical foot. On occasion, all of the lateral rays have been removed with the great toe and first metatarsal left (Fig 16A-8.). The residual foot is quite functional and produces a better gait than with a trans-metatarsal amputation. The wounds in such procedures are irrigated with antibiotic solutions when the removal has been for major infection. Irrigation is performed with a physiologic solution when the wound has been noninfected. We have left none open to granulate. Ecker and Jacobs reported that only 2 of 18 closed wounds failed whereas 16 of 36 open wounds failed.
This amputation may be performed for deformities resulting from trauma to the toes, loss of tissue, and infection or gangrene due to frostbite, diabetes, arteriosclerosis, scleroderma, rheumatoid arthritis, and similar conditions. McKittrick et al. outlined the indications for transmetatarsal amputation in a diabetic in 1949. Their indications are as true today as they were then. Gangrene must be limited to the toes and should not involve the web space. Infection should be controlled. The incision should not extend through hypoes-thetic areas or through infected areas. The patient should be free of pain. Palpable foot pulses are not necessary, but there should be no dependent rubor. Venous filling should be less than 25 seconds. To these criteria, we have added the transcutaneous Doppler ultrasound ischemic index. Healing has occurred in over 93% of our diabetics when the ratio was over 0.45 and in the nondiabetics when it was over 0.35.
A slightly curved incision traverses the dorsum of the foot obliquely at the level of the metatarsal necks (Fig 16A-9.,A). It slants posteriorly to the lateral side approximately 15 degrees so that the residual foot will correspond to the break of the shoe. It continues on either side to half the thickness of the foot. It goes across the plantar surface of the foot just proximal to the base of the toes (Fig 16A-9.,B). The incision is carried sharply to bone, and the metatarsals are divided at the proximal level of the incision (Fig 16A-10.). The periosteum is dissected distally, which then allows easier division of the metatarsal shafts. After division of the bone, the distal part of the foot is raised dorsally and divided from the plantar flap by an oblique incision. To remove pressure points from the plantar surface of the metatarsal shafts, they are beveled or rounded on their inferior edge. Wound irrigation is carried out to remove minor bits of debris from bone division. A Kritter irrigation tube is then introduced into the wound through a separate stab incision (Fig 16A-11.). The flap is enclosed with a single layer of nonabsorbable sutures. A light compression dressing is applied.
Postoperative Treatment and Function
The Kritter drain is removed in several days, and a walking cast is applied at 2 weeks. The residual foot heals rapidly, and most patients are able to use an ordinary shoe. On occasion, the lever arm of the distal part of the shoe can raise the pressure at the end of the amputation. In these cases, the sole is thickened, stiffened, and rockered. This will then imitate the action of the roll-off at the metatarsophalangeal joint (Fig 16A-12.).
Lisfranc and Chopart Amputations
Lisfranc and Chopart amputations were introduced before blood transfusions, antibiotics, and anesthesia were available. They had been planned as disarticulations, to be performed as rapidly as possible, with soft-tissue instruments alone, without the need for cutting bone. Except in special circumstances, there is much less indication for their use at present. There are late complications associated with equinus deformity and resulting increased plantar pressure (Fig 16A-13.). Some of the later problems may be prevented by transfer of the peroneus brevis to the cuboid and transfer of the anterior tibial tendon to the neck of the talus. Lengthening of the Achilles tendon will lessen some of the equinus deformity. If these amputations are performed for an infected gangrenous foot, it is not wise to attempt tendon transfers at the time of the initial surgery. Stabilization can be performed at a later date in most cases. We have also had success at these levels by adding subcutaneous tenotomy of the Achilles tendon and subsequent use of a polypropylene ankle-foot orthosis to the basic technique (Fig 16A-14.).
At Rancho Los Amigos Medical Center, a further technique has been developed for the Lisfranc amputation in which the bases of the fourth and fifth metatarsals are divided from the distal metatarsal shafts and thus save the function of the peroneus brevis tendon. In the Chopart amputation, the anterior tibial tendon and extensor digitorum longus tendons are drawn down and incorporated in the skin closure so that they are attached to the plantar fascia and aid in dorsiflexion.
The procedure is demonstrated on a patient with diabetes mellitus who has a deformed infected forefoot. Bed rest and intravenous antibiotics have allowed regression of the surrounding cellulitis (Fig 16A-15.). There is still marked drainage from a plantar ulcer. Roentgenograms have shown osteomyelitis of the first, second, and third metatarsal heads.
The proximal incision passes over the dorsum of the foot at the base of the metatarsals (Fig 16A-16.). The plantar incision is placed distally so that the infected material is removed but the flap is long enough that it may be tailored later to cover the ends of the resected bones (Fig 16A-17.). The tarsometatarsal joints are disarticulated at the first, second, and third metatarsal bases. The fourth and fifth metatarsal bases are cut through with a motorized saw and left in the residual foot. On occasion, it may be necessary to leave the third metatarsal base in place to provide a better surface to support the local soft tissues (Fig 16A-18. and Fig 16A-19.). The residual foot is then dissected from the plantar surface, starting at the level of the short flexor muscles. The flap is then beveled to the distal edge. The wound is then checked for any residual infectious tissues. It is tailored to close without tension (Fig 16A-20.). A Kritter tube is used to irrigate the wound postoperatively for 24 to 72 hours, depending upon the degree of preoperative infection (Fig 16A-21.). A light compression dressing is applied. Cultures have been taken during the procedure and aid in the postoperative antibiotic treatment. After removal of the Kritter tube, the patient is placed into a nonwalking cast. If healing is sufficient at 2 weeks, the patient is then allowed to ambulate in a cast. This is continued until healing is secure and the patient begins shoe trials.
The residual foot is shorter than that of a transmeta-tarsal amputation (Fig 16A-22.). Occasionally, an ankle-foot orthosis is required (see Fig 16A-14.).
Ablation of the forefoot at the talonavicular and calcaneocuboid joints closely parallels that of amputation at the tarsometatarsal joints. The plantar flap is long enough to fold up to the dorsum of the foot. In infected cases, no bone trimming is performed. In noninfected cases, the distal surfaces of the calcaneus are rounded to relieve potential pressure points. A percutaneous lengthening of the Achilles tendon is performed through three stab incisions: two medially and one laterally. The anterior tendons are sewn into the wound to aid in dorsiflexion.
A prosthetic device is necessary to allow standard shoe wear. If distal pressure ulcers arise despite rocker-ing of the shoe, it may be necessary to revise the residual stump by transferring the anterior tibial tendon into the center of the neck of the talus. Additional rounding of the calcaneus may be necessary, as well as further lengthening of the Achilles tendon.
SURVIVAL OF THE CONTRALATERAL LIMB
A high percentage of dysvascular patients will have an amputation on the opposite side within 3 to 5 years.Many will not have survived. Elderly bilateral amputees do poorly with any level that does not save the knee.For this reason, all efforts should be directed toward partial-foot amputations if preventive measures are not successful. Revascularization procedures should be considered to allow lower amputations to be performed.
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Chapter 16A - Atlas of Limb Prosthetics: Surgical, Prosthetic, and Rehabilitation Principles