Above-the-Knee Amputations

Anatomy and Physiology

The thigh divides into three compartments: anterior, posterior, and medial. These compartments surround the only bone in the thigh, the femur. The anterior compartment contains the vastus lateralis, vastus intermedius, vastus medius, rectus femoris, and genu articularis. Branches of the femoral nerve lie within the anterior compartment and innervate the musculature. A cutaneous nerve, the saphenous, arises from the femoral nerve and innervates the medial skin of the thigh and leg. The iliotibial band runs along the lateral border of the thigh, superficial to the vastus lateralis. The sartorius muscle is in the anterior portion of the thigh more proximally and in the medial portion more distally as it travels from the anterior superior iliac spine to its insertion on the anteromedial aspect of the proximal tibia as part of the pes anserinus. The medial compartment of the thigh contains the adductor magnus, adductor longus, adductor brevis, and gracilis. These muscles receive their innervation from the obturator nerve, except for the adductor magnus, which also receives innervation from the sciatic nerve. The medial compartment also contains the femoral artery and vein, which pass posteriorly after going through the adductor hiatus.[1]

Proximally, the femoral artery divides into superficial and deep branches, with the deep branch providing blood flow to the muscles of the thigh and the femoral shaft. The great saphenous vein runs superficially along the medial aspect of the thigh. The posterior compartment contains the long and short head of the biceps femoris, semitendinosus, semimembranosus, and sciatic nerve. Branches of the sciatic nerve innervate the musculature of the posterior compartment.

Indications

Above-the-knee amputations may be necessary for many reasons. These can include trauma to the lower leg, which results in a non-viable leg at or near the level of the knee. Below-the-knee amputation may adequately address a more distal injury. Many studies have attempted to create algorithms to help physicians decide when to reconstruct versus amputate. One of these is the Mangled Extremity Severity Score (MESS), which takes into account skeletal/soft tissue injury, limb ischemia, shock, and patient age.[2]

Other indications include infection, which has compromised the entire lower leg and is unresectable. Etiologies may include non-healing diabetic wounds, necrotizing fasciitis, or cases of immunocompromised patients. Tumors that are unresectable or whose resection would render the distal aspect of the limb non-usable are yet another indication for this procedure. Vascular compromise, whether from injury or disease, which cannot be corrected, can also necessitate an AKA. Additionally, congenital disabilities that render a limb non-usable can indicate the need for this amputation.

Contraindications

Once all other non-amputation treatment options have been exhausted, there are few contraindications to above-the-knee amputation. An example is if the patient is not medically stable enough to survive the anesthesia and/or surgery. However, it merits consideration that the condition of the patient’s limb may be the cause of their medical instability.

Equipment

In addition to standard operating room set-up, table, and sterile drapes, other needed equipment will vary by surgeon preference but typically includes an orthopedic set with retractors, clamps, etc. An oscillating saw or Gigli saw, a scalpel, and a drill will also be needed. Variable sutures and ties of the surgeon's preference are another necessity for tying off vessels. A suction drain is typically used as well as a device of the surgeon’s preference for wound closure. Additionally, some surgeons may choose to use a sterile tourniquet to reduce blood loss. Radiology is not routinely necessary, but one must make sure the patient is on a radiolucent bed if it is needed intraoperatively. 

Technique or Treatment

Patient placement is supine on the operating room table with the buttock of the surgical side elevated on a stack of blankets. The operative leg gets prepped and draped in a sterile fashion. Planned skin incisions are marked. Some surgeons prefer anterior and posterior skin flaps for a fishmouth type closure with a slightly longer anterior flap, while others prefer medial and lateral flaps. In a traumatic setting, flaps may be dictated by what tissue remains viable. An optional sterile tourniquet is then applied to reduce blood loss. Incisions are then made along the planned lines, and electrocautery is used to control bleeding. Dissection is performed through the underlying fascia. Depending on the level of the amputation, muscle groups are identified and transected with electrocautery. Muscle groups should be transected approximately 1 to 2 inches longer than the planned bony cut to allow for musculature coverage of the bony end and myodesis. The femoral artery and vein are identified, dissected, ligated, and transected. A similar procedure is performed if encountering any other large vessel branches. Next, the sciatic and saphenous nerves are identified and dissected. Gentle traction is applied, and the nerves are sharply transected to reduce the risk of neuroma formation. A similar procedure is performed for any other nerves encountered, depending on the level of the amputation.

Transection of the femur is typically 12 cm proximal to the joint line, but other factors may dictate the level.[3] A Gritti-Stokes amputation involves cutting the femur at the level of the adductor tubercle and arthrodesis of the patella to the end of the cut femur for improved end-bearing. Care must be taken to remove the synovium to avoid postoperative effusion. The bony cut is made with an oscillating saw, and a rasp is used to smooth the edges. Drill holes are made in the lateral and posterior aspects of the distal portion of the remaining femur. The adductor magnus tendon is then sewn to the lateral aspect of the femur with a nonabsorbable suture with the leg held in 5 to 10 degrees of adduction. The quadriceps musculature the then brought over the distal end of the femur and sewn with nonabsorbable suture to the posterior aspect of the femur while holding the hip in full extension. The posterior musculature may undergo myodesis to the posterior aspect of the adductor magnus complex. The fascia lata then gets sutured to the medial fascia. An optional drain may be placed deep to the fascial layers to reduce hematoma. The fascia, subcutaneous tissue, and skin are sutured closed in a layered fashion. Care must be taken not to overtighten the skin suture so as not to cause necrosis. Sterile soft dressings are then applied. An optional splint or cast can then be placed over the remaining stump. 

Complications

Complications following above-the-knee amputation include muscle atrophy, surgical site wound infections, dehiscence, and wounds from prosthetic wear. One can minimize the complications from skin breakdown when they are caught early by checking the skin daily, especially in patients who have an insensate stump. Additionally, certain pre-operative measures may be used to predict a patient's ability to heal an amputation. Albumin over 3.0g/dL, total lymphocyte count greater than 1500/mm^3, and ankle-brachial index greater than 0.45 have been shown to improve wound healing.[4]

Abduction and flexion contractures may also occur as a complication. One study found that 4 of 8 patients who did not have their iliotibial band fixed to the femur to avoid developing an abduction contracture ended up developing a hip flexion contracture; this is believed to have occurred because the gluteus maximus, a hip extensor, inserts in part onto the iliotibial band.[5] The risk of flexion contracture is reducible by having the patient intermittently lie prone post-operatively. Also, myodesis of the quadriceps with the hip in a fully extended position in the OR can reduce this risk. Abduction contracture risk can be decreased by properly performing a myodesis of the adductors to the femur. Phantom limb pain is another complication of an AKA and has been estimated to affect up to 80% of patients who undergo a limb amputation.[6] Post-traumatic stress disorder (PTSD) and depression are known as psychologic complications of amputation. Elderly patients with chronic pain and those who undergo a traumatic amputation demonstrate a higher prevalence of these disorders. Patients who undergo an AKA as a result of chronic illness have lower rates of PTSD.[7]

Clinical Significance

Above-the-knee amputations can have a significant clinical impact on the lives of patients. Many patients do not have the resources to obtain a prosthesis and may have to continue using a wheelchair following the procedure. For those who do get a prosthesis, their mobility is significantly affected. One study showed that patients with a unilateral transfemoral amputation had a self-selected walking speed 8.6% slower than their non-amputee counterparts.[8] Another study showed a 49% increase in oxygen consumption during ambulation in patients with an above-the-knee amputation.[9] Approximately 65% more energy expenditure is required to ambulate in above-the-knee amputees when compared to patients without an amputation.[10] This number can be increased to 100% when the amputation is performed due to vascular compromise compared to trauma. This increased energy expenditure and decreased mobility may ultimately affect both the personal and professional lives of these patients.

Enhancing Healthcare Team Outcomes

An above-knee amputation is associated with enormous morbidity; unlike a below-knee amputation, fitting a prosthesis for an above-knee stump is difficult. In fact, most patients cannot adapt to an above-knee prosthesis and eventually succumb to a wheelchair to get around. This leads to other complications like pressure sores, inability to perform daily living activities, and depression. When possible, clinicians need to avoid an above-knee amputation because of the high morbidity; if the procedure is elective, presurgical education of the patient is important. Both the pre and postoperative management of an above-knee amputation is best managed by an interprofessional team because there are functional and physical issues that need to be dealt with.

An interprofessional approach is essential in caring for patients who have undergone an amputation. Aside from the physician performing the procedure, specialists in other fields of medicine can play a role in improving a patient's outcome. Internal medicine physicians can control and treat comorbid conditions, which may otherwise slow a patient's progress. Nurses are essential to monitoring vital signs, assisting the patient with daily activities, and delivering medication. The wound care nurse is vital to ensure that the stump is healing; unless the wound has healed, a prosthesis cannot be fitted. 

Pharmacists help with prescribing appropriate medications to control pain, prevent thrombosis, and decrease infection risk. Physical therapists guide the patient in rehabilitation protocols to restore muscle function and regain mobility in the absence of a limb. Prosthetists ensure the patient has an appropriate, well-fitting prosthetic. Psychologists and psychiatrists can be a valuable asset to the treatment team if the patient develops symptoms of PTSD or depression. One study, which reviewed 233 patients over 5 years, showed that a team approach to the care of amputees could decrease inpatient stay by 20 days, increase the number of patients discharged with a prosthesis by five-fold, and increase the effectiveness of rehabilitation in the long term setting by threefold.[11] [Level 3]

The outcomes of patients with an above-knee amputation depend on the reason why the surgery was necessary. For those with peripheral vascular disease, the outcomes are guarded; many also have associated heart disease, which can often lead to death. For those undergoing amputation for trauma, the prognosis is good.

In summary, caring for patients with above-the-knee amputation requires an interprofessional team approach, including physicians, specialists, specialty-trained nurses, physical and occupational therapists, and pharmacists, all collaborating across disciplines to achieve optimal patient results.[12] [Level 5]