Transfemoral Amputation: Surgical Management

Frank A. Gottschalk MD^*

COL Benjamin Kyle Potter MD, FAAOS, FACS

Dr. Potter or an immediate family member serves as an unpaid consultant to Biomet and serves as a board member, owner, officer, or committee member of the Society of Military Orthopaedic Surgeons.

^* Deceased.

ABSTRACT

To maintain femoral alignment that is close to normal, it is necessary to consider the biomechanics and surgical technique of transfemoral amputation. Muscle preservation and myodesis of the adductor magnus muscle is necessary for maintaining muscle tension to hold the femur in its anatomically adducted position. Adductor magnus and quadriceps muscle myodesis over the end of the femur also provides an adequate soft-tissue end pad to reduce discomfort and improve the likelihood of successful prosthesis use. Developing appropriate soft-tissue flaps allows uncompromised wound healing and early mobilization of the patient. Various wound care options help reduce healing problems.

Introduction

Transfemoral amputation often is necessary in patients who have nonreconstructible peripheral vascular disease, diabetic foot infection, severe lower limb trauma, or, less commonly, a massive infection or a tumor that cannot be managed with intercalary resection. In these patients, amputation at a level below the femur is unlikely to heal. The incidence of lower limb amputation, including transfemoral amputation, remained unchanged in the Netherlands during the 2 decades leading up to 2004.¹ Patients with diabetes mellitus, especially those older than 45 years, were at greater risk for amputation than the general population.

Most patients with transfemoral amputation must expend at least 65% more energy than normal to walk at a self-selected speed on a level surface.²^,³ This limitation can be compounded by the patient’s underlying medical condition; for example, many patients with a dysvascular disorder lack the physical reserve necessary for functional walking with a transfemoral prosthesis or are otherwise unsuccessful in becoming ambulatory with a prosthesis.⁴ Regardless of concomitant medical conditions, patients with a lower limb amputation were found to be unable to achieve normal gait in terms of velocity, cadence, or walking economy.¹^,⁵ Patients whose transfemoral amputation was necessitated by a nonvascular cause required increased energy expenditure for walking and had limited ambulation and difficulties related to prosthesis use.⁶ Children with transfemoral amputation walked more slowly and with an increased energy cost compared with unaffected children.⁷

Although many improvements have been made in prosthesis design and fabrication, even the best prosthesis cannot adequately replace the limb in the absence of a proper residual limb. Too often, the surgical procedure is done without consideration of biomechanical principles or preservation of muscle function. A major goal of amputation surgery is primary wound healing, but the biomechanical principles of lower limb function should not be sacrificed to achieve this goal. Appropriate muscle anchorage and stabilization can improve wound healing potential by limiting shear force, tension, and motion at the terminal skin interface.

During a transfemoral amputation procedure, it is important to maintain a residual limb with as much length as possible. The longer the remaining femur is, the easier it will be to suspend and align a prosthesis. In addition, leaving the longest possible residual limb will provide the patient with optimal functional ability because the long lever arm can help with transfers and sitting balance.⁸ A long residual limb also reduces the potential for bone erosion through the soft tissues (Figure 1). Bone protrusion through soft tissue can occur as the adductors and quadriceps retract from the end of the femur after inadequate stabilization of the muscles. In a long amputation, there is less abduction force because of the remaining counterforce in the adductor muscles. A study of military patients with transfemoral amputation found that those with a longer residual limb
achieved greater self-selected walking velocity.⁵ The study did not determine whether residual limb length or femoral orientation affected the energy expenditure.

In some patients, the prevailing local pathology may require a proximal transfemoral amputation. If possible, a small portion of the femur should be left at the trochanteric level to provide additional contouring for fitting of a prosthesis. A patient with less than 5 cm of bone distal to the lesser trochanter ultimately may be fitted with a prosthesis designed for a hip disarticulation.

FIGURE 1 Photograph shows a transfemoral amputation with distal soft-tissue loss, bony prominence, and discoloration of skin.

Biomechanics

Normal Alignment

The normal anatomic and mechanical alignment of the lower limb has been well defined⁹^,¹⁰^,¹¹ (Figure 2). The mechanical axis of the lower limb runs from the center of the femoral head through the center of the knee to the midpoint of the ankle. In a normal two-legged stance, this axis is 3° from vertical, and the femoral shaft axis is 9° from vertical. The normal anatomic alignment of the femur is in adduction. This alignment allows the hip stabilizers (the gluteus medius and gluteus minimus) and abductors (the gluteus medius and tensor fasciae latae) to function normally and reduce the lateral motion of the center of mass of the body, thus producing a smooth and energy-efficient gait pattern.

FIGURE 2 Schematic drawing shows the mechanical and anatomic axes of normal lower limbs. A = ankle, H = hip, K = knee, S = shaft axis, T = transverse axis, V = vertical axis. (Reproduced with permission from Gottschalk FA, Kourosh S, Stills M, McClellan B, Roberts J: Does socket configuration influence the position of the femur in above-knee amputation? J Prosthet Orthot 1989;2[1]:94-102. © 1989 American Academy of Orthotists.)

FIGURE 3 AP radiograph of the lower extremity of a patient shows a knee disarticulation with the femur in normal mechanical and femoral shaft axis alignment. The left femur has undergone a transfemoral amputation after adductor magnus myodesis with the femur in adduction and nearly normal alignment.

In most patients with a transfemoral amputation, mechanical and anatomic alignment is disrupted because the femur no longer is in its natural anatomic alignment. The standard anterior-posterior soft-tissue flaps disengage the adductors of the femur and allow the unopposed abductors to displace the femur in an abducted position, compared with the contralateral limb.¹² In a conventional transfemoral amputation, most of the adductor muscle insertion is lost. Particularly affected is the adductor magnus, which has an insertion on the adductor tubercle at the distal medial femur as well as the posterior aspect of the femur on the linea aspera. Femoral alignment is maintained in a knee disarticulation because the adductor mechanism is not disrupted; in addition, the contour of the distal residual limb and soft-tissue envelope constrains the distal femur within the socket (Figure 3).

Conventional surgery results in the loss of the distal third of the attachment of the adductor magnus, and the femur drifts into abduction because of the relatively unopposed action of the abductor system.⁸^,¹² The surgeon sutures the residual adductors and the other muscles around the femur with the residual femur in an abducted and flexed position. This abducted position leads to a side lurch and increased energy consumption during ambulation. Because the original insertions of the adductor muscles are lost, the effective moment arm of these muscles becomes shorter. The remaining
smaller mass of adductor muscle is unable to generate the greater force needed to hold the femur in its normal position, and an abducted position results⁸^,¹³ (Figure 4).

FIGURE 4 AP radiograph shows abduction of a residual femur resulting from inadequate muscle stabilization.

FIGURE 5 Schematic drawing shows the moment arms of the three adductor muscles in a normal limb. Loss of the distal attachment of the adductor magnus results in a 70% loss of adductor strength. The vertical dashed lines show moment arms of the adductor brevis, adductor longus, and adductor magnus muscles. The solid lines are the resultant forces of the respective muscles. The dashed horizontal lines show the levels of proposed amputation. AB = adductor brevis, AL = adductor longus, AM = adductor magnus

Prosthetists recognize that residual femoral abduction compromises function. Several prosthetic socket designs represent an attempt to hold the residual femur in a more adducted position by adjusting the socket shape or using the ischium as a fulcrum.¹⁴^,¹⁵ A radiologic study, however, revealed that the position of the residual femur after transfemoral amputation cannot be controlled by the socket shape or alignment.¹⁶ Attempting to stabilize the soft tissues in adduction within the socket does not influence the position of the femur.

Of the three adductor muscles (the adductor magnus, adductor longus, and adductor brevis), the adductor magnus has the moment arm with the best mechanical advantage.¹²^,¹⁶^,¹⁷ Figure 5 shows the directions of the components of force of the adductor muscles, with the lines of force joining the points of attachment of the muscles. The adductor magnus is three to four times larger in cross-sectional area and volume than the adductor longus and adductor brevis combined. Transection of the adductor magnus at the time of amputation leads to a major loss of muscle cross-sectional area, a reduction in the effective moment arm, and a loss of as much as 70% of the adductor pull.¹⁶^,¹⁷ The result is overall weakness in the adductor force of the thigh and subsequent abduction of the residual femur. In addition, loss of the extensor portion of the adductor magnus leads to a decrease in hip extension power and an increased likelihood of a flexion contracture.

Muscle Atrophy

A reduction in muscle mass at amputation combined with inadequate mechanical fixation of muscles and atrophy of the remaining musculature was the most important factor responsible for the decrease in muscle strength detected after transfemoral amputation.¹⁸ Decreased strength was most noticeable in the flexor, extensor, abductor, and adductor muscles of the hip and was correlated with inadequate muscle stabilization.¹⁹

Jaegers et al²⁰^,²¹ documented muscle atrophy in 12 healthy patients after transfemoral amputation. Three-dimensional MRI reconstruction showed atrophy of 40% to 60% in hip muscles that had been sectioned. In the intact muscles, which included the iliopsoas, gluteus medius, and gluteus minimus, the atrophy ranged from zero to 30%. The amount of atrophy of the intact muscles was related to the length of the residual limb; there was less atrophy in longer residual limbs. Despite the presence of muscle atrophy, fatty degeneration was not noted. The iliotibial tract was not reattached in an attempt to avoid abduction contracture of the hip. This strategy, however, led to hip flexion contractures for the following reasons: (1) the action of the iliopsoas muscle was unopposed, and (2) the large insertion of the gluteus maximus into the gluteal fascia, which continues into the iliotibial tract, meant that leaving the iliotibial tract unattached weakened the extensor mechanism. The extent of atrophy of the adductor muscles also depended on the level of amputation. In none of the patients was the adductor magnus adequately reanchored. Amputations that were relatively proximal without adequate muscle stabilization led to more muscle atrophy and were more likely to lead to an abduction contracture and atrophy of the gluteus muscles. The gluteus maximus was found to be atrophied in all 12 of the patients. A lack of hamstring fixation led to as much as 70% atrophy. Changes in muscle morphology after amputation are the result of changes in volume and geometry (size and mass). Additional study findings included reduced bone density, cortical atrophy, and increased volume of the femoral medullary cavity.²⁰

Electromyographic Activity

Electromyographic studies reveal adductor magnus activity during normal gait at both the beginning and end of the stance phase and into the early swing phase.²²^,²³ In an electromyographic study of transfemoral amputations by Jaegers et al²¹ the intact
muscles maintained the same sequence of activity as that found in a normal limb, but the activity extended over a longer period. The activity of sectioned muscles depended on the level of amputation and whether the muscles had been reanchored. Muscles that were correctly reanchored remained functional in locomotion, especially in distal transfemoral amputations. Alterations in muscle activity during walking probably were related to the altered morphology of once-biarticular hip muscles, the passive elements of the prosthesis, and the patient’s changed gait pattern. The extent to which the gait was asymmetric was related to the length of the residual limb. The greater the atrophy of the hip-stabilizing muscles was, the greater was the lateral bending of the trunk to the amputation side.²⁴

Surgical Principles

The goal of transfemoral amputation surgery should be the creation of a dynamically balanced residual limb with good motor control and sensation. Preservation of the adductor magnus helps maintain muscle balance between the adductors and abductors by allowing the adductor magnus to maintain close-to-normal muscle power and a mechanical advantage for holding the femur in the normal anatomic position. A residual limb with dynamically balanced function allows the patient to perform at a relatively normal level and to use a prosthesis with greater ease. Several experts recommend transecting the muscles through the muscle belly at a length equivalent to one-half the diameter of the thigh at the level of amputation.²⁵^,²⁶^,²⁷^,²⁸ Muscle stabilization after transection also has been recommended as a means of controlling the femur, but usually it cannot be achieved because the remaining muscle mass had retracted before the transection⁸ (Figure 4). Reestablishing the normal muscle tension, as is customarily recommended, becomes difficult. Many surgeons have attempted muscle stabilization by myoplasty over the end of the femur or myodesis to the femur just proximal to the end of the bone.⁸^,²¹^,²²^,²³^,²⁴ Baumgartner⁸ described using coronal flaps and placing the tissue under tension while transecting the soft tissue and muscles before the femoral osteotomy. Myoplasty, in which the agonist and antagonist groups of muscles are sutured to each other over the bone end, does not restore normal muscle tension or allow adequate muscle control of the femur. The residual femur moves in the muscle envelope, producing pain and occasionally penetrating the soft-tissue envelope. Often, a bursa develops at the end of the cut femur. The loss of muscle tension leads to a loss of control and reduced muscle strength in the residual limb. The soft-tissue envelope around the distal end of the residual limb is unstable and may compromise prosthetic fitting. Instead of myoplasty, a muscle-preserving myodesis technique in which the distal insertions of the muscles are detached from their bony insertion and reattached to the residual femur under close-to-normal muscle tension is preferred. After the myodesis is completed, any redundant tissue can be excised.¹²

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