Transtibial Amputations

Abstract

The transtibial amputation is one of the most frequently performed major limb amputations in the United States. The long posterior flap technique has become the most frequently recommended technique; however, the surgeon performing amputations needs to be comfortable with the alternative techniques as well. Situations occasionally do arise where the sagittal or skew techniques may be more applicable. With careful surgery and soft tissue handling, wound healing can be expected in the majority of patients. Aggressive rehabilitation is possible in many patients, and with good prosthetic intervention, return to ambulation at or near the preoperative level of function can be expected in most patients.

Transtibial amputations are performed because of gangrene, ischemia, infection, severe deformity of the foot, massive trauma, or tumors. From 1988 to 1992 there were an estimated 130,000 amputations performed yearly in the United States. This estimate comes from adding the National Hospital Discharge Survey's estimate of 110,000 amputations performed annually, plus the Department of Veterans Affairs Hospitals estimate of 17,000 amputations performed annually, and adding the lesser number of amputations performed annually estimated from the military, private charitable, and Indian Services hospitals.²⁴ Even though persons with diabetes represent only approximately 3% of the total United States population, 51% of the discharge diagnoses for amputation also listed the diagnosis of diabetes. Using these numbers, approximately 65,000 individuals with diabetes undergo lower extremity amputations per year.²⁴

Table 1 shows the estimated breakdown of the percentage of lower extremity amputations performed by surgical amputation level for persons with and without diabetes, based on the National Hospital Discharge Survey data. Although the rate of transfemoral amputations has decreased dramatically in the last 20 years, the statistics from the National Hospital Discharge Survey indicate that overall, slightly more transfemoral amputations are done each year than transtibial amputations. The data (Table 1) show that in persons with diabetes, the ratio of transtibial to transfemoral amputations are slightly more favorable, but closer than many experts think.²⁴

TABLE 1: Lower Extremity Amputations be Amputation Level and the Presence of Diabetes (National Hospital Discharge Survey Data 1989-92)²⁴

The long posterior flap technique generally has become standard surgical technique for a transtibial amputation, and good results can be expected even in a majority of patients with vascular compromise.^{4-7,14,17-19,21} Anteroposterior (AP), sagittal, and skewed flaps all have been described and occasionally can be useful in specific patients. The blood supply to all of these flaps has been detailed in a excellent review by Humzah and Gilbert.¹⁰ They described the difference between random flaps and fasciocutaneous flaps, and describe the blood supply to the different flaps used in transtibial amputations. the level of tibial transection should be as long as possible between the tibial tubercle and the junction of the middle and distal thirds of the tibia, based on the available healthy soft tissues. Amputations in the distal third of the tibial should be avoided because they have poor soft tissue padding, and tend to be more difficult to fit comfortably with a prosthesis. Additionally, with a very distal transtibial amputation the final prosthesis is bulky near the ankle and less anatomic in appearance. Because of the lack of clearance and limited space below the socket the choice of prosthetic foot and ankle components is also more limited.

LEVEL SELECTION IN PATIENTS WITH DIABETES AND VASCULAR DISEASE

Ischemia from peripheral vascular disease remains the most frequent reason for amputation in patients today. Approximately ½ of these patients also have diabetes. The preoperative evaluation of these patients is complex, and includes the clinical examination and evaluation of the tissue quality, level of tissue necrosis from infection, perfusion, nutrition, immune status, and functional abilities. Preoperative screening tests to measure perfusion directly or indirectly can be helpful, but no one test is 100% accurate, and all of these tests have false negative rates. Clinical judgment is still an extremely important factor in the preoperative assessment of patients with diabetes or peripheral vascular disease.^{3-5,8,13,23,27,28}

Doppler ultrasound blood pressure assessment is the most readily available objective measurment of limb blood flow and perfusion. Arterial wall calcification increases the pressure needed to compress these vessels, often giving an artificially elevated reading. Low pressures are indicative of poor perfusion. Normal and high pressures can be confusing because of vessel wall calcification, and are not predictive of normal perfusion or of wound healing. Digital vessels are not usually calcified, and toe blood pressures seem to be more predictive of healing than ankle pressures.^3,23

Transcutaneous oxygen tension measurements are noninvasive and are becoming more readily available in many vascular laboratories.⁵ These tests measure the partial pressure of oxygen diffusing through the skin with a special temperature controlled oxygen electrode. The ultimate reading is based on several factors: the oxygen delivery to the tissue, the oxygen use by the tissue, and the diffusion of the gas through the skin. Cellulitis and edema can increase use, and decrease diffusion, thereby giving lower values than if the cellulitis and edema resolve. Caution in interpretation of transcutaneous pO₂ measurements during acute cellulitis or edema is warranted. Also, a paradoxical response of transcutaneous pO₂ to warming on the plantar foot skin has been reported recently, and warrants caution in interpreting plantar foot transcutaneous pO₂ values.²⁸ Transcutaneous pO₂ has been shown to be statistically accurate in predicting amputation healing, but false negatives still exist, and many measurements fall into a gray zone for predicting healing.

Xenon 133 skin clearance has been reported as predictive of healing of amputations. The preparation of the xenon 133 gas and saline solution and the application of this test are high technician dependent, expensive, and time consuming, and is no longer recommended.¹³

Arteriography has not been helpful in predicting successful healing of amputations, and this invasive test is probably not indicated solely for the purpose of level selection. Arteriography is indicated if the patient is truly a candidate for arterial reconstruction or angioplasty.

Nutrition and immunocompetence have been shown to correlate directly with amputation wound healing. Many laboratory tests are available to assess nutrition and immunocompetence, and some are quite expensive. Albumin and total lymphocyte count are readily available and inexpensive screening parameters. Several studies have shown increased healing of amputations in patients with vascular disease who had a serum albumin level of at least 3 or 3.5 g/dL, and total lymphocyte count greater than 1500 cells per cubic millimeter.^8,21,22 Preoperative nutritional screening is recommended to allow nutritional improvement preoperatively, or consideration of a higher level amputation. Cigarette smoking also has been shown to increase the risk of infection and reamputation for patients undergoing lower extremity amputations.¹¹ Despite these issues, recent series of patients with diabetes show that successful wound healing still can be achieved in 70% to 80% of these patients at the transtibial or more distal amputation levels.²²

Activity level, ambulatory potential, cognitive skills, and overall medical condition must be evaluated to determine if the distal-most level is really appropriate for the patient. In patients who are likely to remain ambulatory, the goal is to achieve healing at the distalmost level that can be fit with a prosthesis, and to successfully rehabilitate the patient.

GOALS

The goals of a transtibial amputation are to obtain primary wound healing, avoid infection, and create a well padded residual limb that easily can tolerate the stresses of prosthetic fitting and full weightbearing. The surgical result should be a cylindrical shaped residual limb, not a conical shaped limb, because the cylindrical shape is mush better suited to total contact prosthetic fitting techniques. A well padded, cylindrical shaped limb is best achieved with muscle stabilization up over the anterior tibia, and securing this to the periosteum or to drill holes in the tibia. The exact placement of scars is not as important as avoiding scars that are adherent to bone. The perioperative goals also include the avoidance of knee flexion contractures, and facilitation of aggressive rehabilitation. Although the energy requirements for ambulation do increase after amputation,²⁹ a return to the preamputation ambulatory level is a very reasonable rehabilitation goal for most patients.²¹

SURGICAL TECHNIQUES

Long Posterior Flaps

The long posterior myocutaneous flap technique was popularized in the United States by Burgess et al^4-7 and Pedersen.^17-19 This technique provides good distal end padding, and a cylindrical shaped residual limb. The flap is designed with a flap length equal to the diameter of the limb at the level of bone transection plus 1 cm. The flap length is longer than often is thought necessary because the center of rotation for this flap is posterior to the calf (Fig 1).

Fig 1: Schematic drawing of a long posterior flap technique for transtibial amputation. The posterior flap length is equal to the diameter of the limb at the level of bone transection plus 1 cm (rotation of this flap occurs posteriorly, not at the midpoint in the AP plane). The fibula is divided 1 to 2 cm shorter than the tibia to avoid distal fibula pain in the prosthesis. A bevel is placed on the anterior tibia to minimize distal tibial pain. The fascia of the posterior flap is secured up over the tibia with myoplasty or myodesis techniques, to prevent loss distal padding.

The skin and subcutaneous tissue should not be separated from the muscular investing fascia as commonly is shown when this technique is illustrated. Keeping the layers together preserves skin perfusion. The deep posterior compartment muscles are resected at the level of the tibial transection. Traditionally the gastrocnemius and soleus were retained as a beveled muscle flap.^4,5 The authors prefer to keep the muscles intact and not bevel across the muscle bellies, but rather retain the deep muscular investing fascia. In very edematous limbs, or where the soleus appears dusky but the gas trocnemius healthy, the soleus can be resected in its entirely. Soleus resection often yields an extremely suitable, healthy flap based on only the gastrocnemius muscle, that can contour over the tibia with less tension than before soleus resection. With proximal third transtibial amputations, especially in large legs, resection of the soleus and preservation of the gastrocnemeus muscle also may be performed to reduce the bulbous shape of the end of the residual limb. In all cases, the fascia from the long posterior flap should undergo myodesis up over the tibia to the periosteum or to drill holes place anterior on the tibia to prevent retraction of the posterior flap.

Skew Flaps and Sagittal Flaps

The skew and sagittal flap techniques are variations of medial and lateral flap techniques, with slightly oblique flaps of equal length with an axis offset from the AP plane (Fig 2). The skew flap technique was popularized by Robinson et al²⁵ in England, and the anteromedial and posterolateral fasciocutaneous flaps were designed based on their cutaneous skin perfusion studies. The fasciocutaneous flaps are elevated from the underlying muscle to expose the deeper structures. The anterior and lateral compartment muscles are transected at the level of the bone cut, then the tibia and fibula are divided. The deep posterior compartment muscles also are transected at the level of the bone cut, whereas the superficial posterior muscle flap is preserved and contoured for myoplasty over the tibia. The anteromedial and posterolateral fasciocutaneous flaps then are closed in an oblique fashion.

Figure 2: The skew flap, popularized by Robinson et al,²⁵ uses anteromedial and posterolateral cutaneous flaps based on research of the cutaneous skin perfusion, and incorporates a long posterior muscle myoplasty over the tibia. The sagittal flap, popularized by Alter et al¹ and Persson,²⁰ uses antrolateral and posteromedial musculocutaneous flaps based on the underlying muscle groups and major vessels, and also incorporates a myoplasty with the anterior compartment muscle and medial gastrocnemius muscle over the tibia.

The sagittal flaps are musculocutaneous flaps based on the underlying muscle groups and major vessels of the anterolateral compartment, and the medial head of the gastrocnemius in the posteromedial aspect of the leg.^1,20 In the sagittal technique, the anterior and lateral muscles are preserved with the overlying skin, and distal padding is achieved by bringing the anterior compartment muscles and the medical gastrocnemius muscle together as a myoplasty over the tibia. The sagittal technique is often a good option when adequate posterior tissue is not available, or after a short guillotine open amputation.

Equal Anterior and Posterior Fishmouths Flaps

Although this technique occasionally is still described, its use should be avoided because of the relatively thin anterior skin. It is more difficult to achieve good distal padding, and the resulting residual limb often is very conical. Where adequate posterior tissue is not available to create a functional soft tissue envelope.

Nerves

All of the nerves, superficial and deep peroneal, posterior tibial, saphenous, and sural nerves should be identified, drawn down, resected, and allowed to retract at least 3 to 5 cm away from areas of pressure, scar, and pulsating vessels. The sural nerve often is neglected and can lead to a very symptomatic neuroma on the distal end of the residual limb or the incision line. Care must be taken to specifically identify and resect the sural nerve. Although some controversy exists on the best technique to handle the transected nerves, the literature is not conclusive. There is no definitive evidence that cautery, ligation, end loop anastomosis, or nerve capping are more effective that careful resection. In the authors' opinion, ligation of a nerve is indicated only if the nerve is likely to bleed (the sciatic nerve in a transfemoral amputation). The nerves in the lower leg usually do not require ligation. Several recent studies suggests that interventions designed to block the nerve pathways at the time of amputation surgery do reduce the need for opioid medication during hospitalization, and may decrease the incidence of chronic phantom pain.^2,9,12,15

Bones

The end of the tibia is triangular in cross section. If the tibia is cut perpendicular to the long axis, it leaves a point of bone anteriorly that lies under the thinnest, least padded skin. An anterior bevel should be placed on the tibia, to remove this apex of bone, and to provide a broad, smooth surface that should help to prevent distal pain. The bevel should extend 1.5 cm proximal to the cut end of the tibia at an angle of approximately 30°. In very short transtibial amputations, a smaller bevel should be made to avoid a functional shortening of the tibial lever arm. The fibula should be transected 1 to 2 cm shorter than the tibia. If the fibula is cut the same length as the tibia, the patient senses that the fibula is too long and pain over the distal fibula can complicate prosthetic fitting. If the fibula is cut too short, a more conical shape residual limb results.

Distal tibiofibular synostosis, the Ertl procedure, rarely is indicated in patients with vascular disease. The principle is to create a broad bone mass terminally to improve the distal endbearing property of the limb. This goal of improved endbearing can be achieved partially, but the complication of a painful nonunion can be difficult to treat. Distal tibiofibular synostosis is indicated in a wide traumatic diastasis of the tibia and fibula. In these traumatic cases, surgical synostosis can improve stabilization of the bone and soft tissues. In the patient with trauma this can be achieved by moving a 1 cm section of fibula as graft into the syndesmosis and placing a 3.5 or 4.5 mm screw through the fibula, through the graft, and into the tibia. Care should be taken to assure that the proximal tibiofibular joint is reduced.

REHABILITATION

The transtibial amputation is especially well suited to rigid dressings and immediate postoperative prosthetic management. Protocols for weightbearing in these casts continue to be debated.¹⁶ The following are the authors' preferred perioperative rehabilitation protocols for the most common patient populations:

Patients With Vascular Disease or Diabetes

A long leg amputation cast (to the proximal thigh) with a good supracondylar mold is applied in the operating room by the surgeon, but the distal attachment plate for the pylon is not applied. The knee should be in 3° to 5° flexion, because full extension or hyperextension can be uncomfortable. The patient works on straight leg raising, gentle towel pulls over the cast, and transfer skills until the first cast change at 5 to 7 days. If wound healing seems to be progressing well, a new long leg amputation cast with a distal pylon and foot is applied, and weightbearing is started at 20 to 30 lb of weight. Most patients are discharged to home with outpatient therapy, and return for cast change in 1 week. The cast is changed weekly by the prosthetist, and weightbearing is advanced by approximately 30 lb each week. When the residual limb appears to have lost the postoperative edema, wrinkles have returned to the skin, and the volume appears unchanged from the previous week, shrinker socks are applied and the prosthetist begins fabrication of the first prosthesis. Commonly one or two socket changes are required during the first 12 to 18 months, so the initial prosthesis is made in a modular fashion to allow socket changes without replacement of all of the components.

Traumatic Amputation Above the Zone of Injury

A long leg amputation cast with a good supracondylar mold is applied in the operating room by the surgeon, and a distal pylon and foot is applied by the surgeon or the prosthetist. The knee should be in 3° to 5° flexion. The patient works on straight leg raising, gentle towel pulls over the cast, transfer skills, and also begins weightbearing at 20 to 30 lb of weight. The first cast change is done at 5 to 7 days. If wound healing seems to be progressing well, a new long leg amputation cast with pylon and foot is applied, and weightbearing is advanced by approximately 30 lb of weight. The patients usually are discharged after the first cast change, to return weekly for outpatient cast changes. Weightbearing is advanced weekly by approximately 30 lb until the residual limb appears to have lost the postoperative edema, wrinkles have returned to the skin, and the volume appears unchanged from the previous week. This usually takes between 3 and 6 weeks. Shrinker socks then are applied and the prosthetist begins fabrication of the first prosthesis. Commonly two or three socket changes are required during the first 12 to 18 months, so the initial prosthesis is made in a modular fashion to allow socket changes without replacement of all of the components.

Traumatic Amputation Involving The Zone Of Injury

Commonly these amputations have some marginal tissue or recent skin grafts. A rigid dressing made of cast or splint material is used to prevent knee flexion contractures, and to protect the limb from outside injury. If open wound care is required, a thermoplastic posterior amputation splint can be fabricated to allow wound care but provide the benefits of splinting, contracture prevention, and pain relief. When the wound is healed a cast and pylon are applied if significant edema is still present. Weightbearing is begun at 20 to 30 lb. If the edema has resolved by the time of wound healing, and wrinkles returned to the skin, the authors occasionally proceed directly to shrinker socks and the fabrication of the first prosthesis. Again, the initial prosthesis is made in a modular fashion to allow socket changes without replacement of all of the components.

Transtibial amputation techniques continue to evolve. With careful surgical techniques, wound healing can be expected in the majority of patients. Aggressive rehabilitation is possible in many patients, and with good prosthetic intervention, return to ambulation at or near the preoperative level of function is possible.