Chapter 20A - Atlas of Limb Prosthetics: Surgical, Prosthetic, and Rehabilitation Principles
Transfemoral Amputation: Surgical Procedures
Frank Gottschalk, M.D., F.R.C.S.Ed., F.C.S.(S.A.)Orth.
It is well accepted that transfemoral (above-knee) amputees have an increased energy expenditure for walking. Even those with no concomitant medical problems are unable to achieve normal gait in terms of velocity, cadence, or walking economy. Older dysvascular amputees do not have the physical reserve required and oftentimes will be limited household walkers or be totally unable to use a transfemoral prosthesis.
Despite improvements in prosthetic design and fabrication, artificial limbs are unable to provide a reasonable replacement for the lost limb when poor surgery has been done and an inadequate residual limb has been created. Too often the procedure is performed without thought for biomechanical principles or preservation of muscle function. Although one of the major goals of surgery is primary wound healing, this can be achieved while maintaining biomechanical principles of lower-limb function. In the majority of transfemoral amputees who have had a conventional surgical procedure, the energy expenditure will be 65% or more above normal for level walking at a regular walking speed. It is important to maintain as much length as possible when doing a transfemoral amputation. The longer the residual limb, the easier it is to suspend a prosthesis as well as to align it. The functional ability of the patient is also improved with a longer residuum. In some circumstances a higher level of amputation may be dictated by the prevailing local pathology. In these cases a small portion of the femur at the trochanteric level should be left where possible. This allows for enhanced prosthetic fitting by providing additional contouring. In those patients where prosthetic use is not considered, as long a stump as possible should be left. This provides a longer lever arm and may help with transfers as well as reduce the potential for bone erosion through the soft tissues.
The normal anatomic and mechanical alignment of the lower limb has been well defined (Fig 20A-1.). In two-legged stance 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 and measures 3 degrees from the vertical. The femoral shaft axis measures 9 degrees from the vertical. The normal anatomic alignment of the femur is thus in adduction, which allows the hip stabilizers (gluteus medius and minimus) and abductors (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 smoother and more energy-efficient gait.
In most transfemoral amputees, mechanical and anatomic alignment is disrupted since the residual femur no longer has its natural anatomic alignment with the tibia, leaving the femoral shaft axis in abduction as compared with the sound limb. The abducted femur of the transfemoral amputee leads to an increase in side lurch and higher energy consumption. In addition, the major portion of the adductor insertion is lost in conventional transfemoral amputations. Only the adductor magnus has an insertion on the mediodistal third of the femur. Once this attachment is lost at the time of surgery, the femur swings into abduction because of the relatively unopposed action of the abductor system. In the usual procedure the surgeon then sutures the residual adductors and the other muscles around the femur with the residual femur in an abducted and flexed position.
As the insertions of the adductor muscles are lost, their effective moment arm becomes shorter. Thus a smaller mass of adductor muscle would have to generate a larger force to hold the femur in its normal position. They are unable to generate this force to hold the femur, and an abducted position is then maintained.
Prosthetists have recognized that residual femoral abduction compromised patient function and that prosthetic fitting of the transfemoral amputee was not satisfactory. Newer prosthetic socket designs have tried to hold the residual femur in a more adducted position by using the ischium as a fulcrum. Another method using prosthetic alignment with adjustment of socket shape is also claimed to better control abduction of the residual femur. A radiologic study of transfemoral amputees revealed that the position of the residual femur could not be controlled by the prosthetic socket shape or alignment.
The adductor magnus has a moment arm with the best mechanical advantage as compared with the adductor longus and brevis (Fig 20A-2.). 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 up to 70% of the adductor pull. This combination results in overall weakness of 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 a greater likelihood of a flexion contracture.
It has been noted that a reduction in muscle mass at amputation, combined with inadequate mechanical fixation of muscles as well as atrophy of the remaining musculature, was the major factor for the decrease in muscle strength detected in transfemoral amputees. Most noticeable was a decrease in strength of the flexor, extensor, abductor, and adductor muscles of the hip, which correlated with inadequate muscle stabilization.
The goal of surgery in a transfemoral amputation should be the creation of a dynamically balanced residual limb with good motor control and sensation. Preservation of the adductor magnus muscle is possible and helps maintain the muscle balance between the adductors and abductors. The retained muscle bulk allows the adductor magnus to maintain close-to-normal muscle power and a better advantage for holding the femur in the normal anatomic position. A residual limb with dynamically balanced function should allow the amputee to function at a more normal level and use a prosthesis with greater ease.
Several authors recommend transecting the muscles through the muscle belly at a length equivalent to half the diameter of the thigh at the level of amputation.Although muscle stabilization is advocated as a means of controlling the femur, in actuality this is infrequently achieved since the remaining muscle mass will have retracted at the time of transection (Fig 20A-3.). It is then difficult to re-establish the normal muscle tension as recommended in the standard texts. A muscle-preserving technique is preferred whereby the distal insertions of the muscles are resected from the bony attachment. Once the myodesis has been done, the remaining tissue can be excised.
INDICATIONS FOR TRANSFEMORAL AMPUTATION
This is probably the most common cause for transfemoral amputation. Although this procedure is done less frequently than in the past, it is often necessary in those patients with very severe vascular and diabetic disease who are deemed to have poor potential to heal a lower-level amputation. The majority of these patients have widespread systemic manifestations of the disease which may often compromise their postoperative rehabilitation. Their physical reserve is often insufficient for them to become prosthetic users. Patients with combined diabetic/vascular disease tend to be an average of 10 years younger than those patients with purely vascular problems (refer to Chapter 2C). Patients with purely vascular disease tend to have a higher incidence of transfemoral amputation.
The majority of patients who require a transfemoral amputation for trauma are generally in the younger age group. Most times the indication for amputation will be severe soft-tissue, vascular, neurologic, and bone injury. Maximum length should be retained, but it is important to have a good soft-tissue envelope and avoid a split-thickness skin graft to bone (refer to Chapter 2B). It is mandatory to do at least a two-stage procedure and leave the wounds open at the initial stage to avoid wound infection and allow for additional debridement if necessary. On occasion, split-skin grafts may be used with a view to secondary skin expansion. Fractures of the femur should be stabilized by appropriate means rather than amputating through a proximal fracture site. The orientation of skin flaps is not critical, but closure should be without tension.
Amputation for severe infection or osteomyelitis should be done as a two-stage procedure with antibiotic coverage. In some situations, the placement of antibiotic-impregnated methacrylate beads is useful for controlling local infection. All infected tissue must be excised (refer to Chapter 2D).
Often the level of amputation is determined by the type and location of the tumors. The principles of tumor eradication need to be considered, while at the same time, as long a stump as possible is preserved. Preservation and restoration of function are important factors (refer to Chapter 2E).
In general, a tourniquet is not used for the majority of transfemoral amputations. If necessary, a sterile tourniquet can be placed as high on the thigh as possible and released prior to setting muscle tension. Skin flaps should be marked out prior to the skin incision (Fig 20A-4.). Anterior flaps are fashioned longer than posterior flaps so that the suture line will be posterior. A long medial flap in the sagittal plane is also acceptable, and any flap configuration that will enhance feasible preservation of length is acceptable in trauma or tumor. One should make the skin flaps longer than may be initially thought necessary to avoid having to shorten the bone too much.
Once the major vessels have been isolated, they should be ligated and cut at the proposed level of bone section. The major nerves should be dissected 2 to 4 cm proximal to the bone cut and sectioned with a new, sharp blade. The central vessel can be lightly cauterized or secured by a stitch tie around the nerve. The placement of a small catheter in the nerve for local anesthetic infiltration is said to decrease the severity of postoperative pain and phantom sensation.
Muscles should not be sectioned until they have been identified. The quadriceps should be detached just proximal to the patella to retain some of its tendinous portion. The adductor magnus is detached from the adductor tubercle by sharp dissection and reflected medially to expose the femoral shaft. It may be necessary to detach 2 to 3 cm of the magnus from the linea aspera. The smaller muscles should be transected approximately 1 to 2 in. longer than the proposed bone cut to facilitate their inclusion and anchorage.
The femur is exposed just above the condylar level and is cut with a power saw using an oscillating blade so that the femur is transected approximately 7.5 to 10 cm above the knee joint line. The blade should be cooled with saline. Two or three small drill holes are made on the lateral cortex of the distal end of the femur 1 to 1.5 cm from the cut end. Additional holes are made anteriorly and posteriorly.
The adductor magnus tendon is sutured with nonabsorbable or long-lasting absorbable suture material to the lateral aspect of the residual femur via the drill holes (Fig 20A-5.). Prior to securing the stitches, the femur is held in maximum adduction, while the adductor magnus is brought across the cut end of the femur while maintaining its tension. Additional anterior and posterior sutures are placed to prevent the muscle from sliding forward or backward on the end of the bone.
Once the adductor magnus has been anchored, the quadriceps is sutured to the posterior aspect of the fe>mur via the posterior drill holes (Fig 20A-6.). The hip should be in extension when this is done to prevent creating a hip flexion contracture. The remaining hamstring muscles are then anchored to the posterior area of the adductor magnus. The investing fascia of the thigh is then sutured as dictated by the skin flaps. Subcutaneous stitches may be used to approximate the skin edges, and fine nylon sutures (3.0 or 4.0) are used to close the skin and are placed no closer than 1 cm apart, especially in dysvascular cases. Fig 20A-7. shows a postoperative roentgenogram with the femur held in adduction by the adductor myodesis.
Although some authors advocate the use of myoplasty alone to anchor the muscles, this technique does not restore normal muscle tension, nor does it allow for adequate muscle control of the femur. At the time of myoplasty the agonist and antagonist groups of muscles are sutured to each other over the bone end. This does not provide a stable situation, and the residual femur moves in the muscle envelope and produces pain. The loss of muscle tension and the inability to restore it leads to some loss of control and reduced muscle strength in the residual limb. The soft-tissue envelope around the distal end of the residuum is unstable and may compromise prosthetic fitting.
The residual limb should be wrapped with an elastic bandage applied as a hip spica with the hip extended. Although rigid dressings control the edema and stump position better than soft dressings do, they are cumbersome to apply and do not offer any great advantage in the long term in transfemoral amputations. A well-applied elastic bandage will not slip off the residual limb.
Another method of controlling the swelling and reducing discomfort is to apply an elastic shrinker with a waist belt. The shrinkers are made of a oneor two-way stretch material that applies even pressure distally to proximally. The waist belt helps prevent the shrinker from slipping off. The shrinker may be applied at the first dressing change at 48 hours.
Postoperative phantom pain is not uncommon and can be reduced by infiltrating the sectioned nerve with bupivacaine (Marcaine) at the time of surgery. A relatively new method is to place a small catheter in the nerve so that local anesthetic can be intermittently administered directly to the nerve. This is only done for 3 to 4 days and then discontinued. A controlled study has confirmed the effectiveness of this method and showed that the amount of postoperative narcotic analgesic could be considerably reduced.
GENERAL POSTOPERATIVE CARE
While the wound is healing, the patient should be mobilized in a wheelchair and in the parallel bars and upper-body exercises started. In addition, conditioning of the well leg should take place. Most often, the sutures can be removed at around 2 weeks for traumatic amputations and at 3 weeks in the dysvascular amputee. During this time the patient will have been wrapping the residual limb or using a shrinker. A temporary plastic adjustable prosthesis can now be fitted and gait training started. The patient needs to have sufficient upper-body strength to use crutches or a walker. Flexion contractures should be prevented from occurring by correct positioning of the patient in bed as well as muscle-strengthening exercises. By using aggressive rehabilitation techniques in a motivated patient, early return to walking can be accomplished in a short time. Those patients who do not have the physical or mental ability to participate in a rehabilitation program designed to teach prosthetic use will be better off using a wheelchair. Transfer training is important in this regard. The decision to provide the patient with a wheelchair should be made early in the postoperative period.
The overall rehabilitation of the patient with a trans-femoral amputation begins at the time of surgery and continues until the patient has achieved maximum functional independence for that individual. The appropriate surgery allows for easier prosthetic fitting as well as enhancing physical therapy to allow the patient to achieve the goals set by the treating team.
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Chapter 20A - Atlas of Limb Prosthetics: Surgical, Prosthetic, and Rehabilitation Principles