Above-Knee (Transfemoral) Amputation - AK Amputation

Definition & Terminology

Indications

• Vascular disease / ischemia extending too proximally to allow a viable below-knee (transtibial) stump - especially when the femoral pulse is absent
• Severe tissue loss from ischemia or infection not salvageable at the BK level
• Failed or non-healing below-knee amputation requiring revision proximally
• Bed-bound patients with severe contracture at the knee (>20 degrees), where an AK stump avoids pressure injury
• Non-ambulatory patients in whom the extra healing reliability of AKA outweighs functional loss
• Malignancy / trauma when the knee or distal thigh is involved

Level Selection and Stump Length

• The femur can be transected as proximal as necessary for skin closure, but ideally is divided in the distal one-third of the femur
• The minimum functional stump length is not less than 20 cm above the knee (Bailey & Love) - enough for adequate leverage
• The optimal transfemoral bone length is approximately 12 cm above the knee joint to accommodate the prosthetic knee unit (Miller's Review of Orthopaedics, 9th ed.)
• Greater femoral length optimizes the lever arm, suspension, and limb advancement for prosthetic function
• The femur is typically divided 2-3 cm proximal to the skin incision corners, using a periosteal elevator to clear the bone at that level

Preoperative Assessment

Surgical Technique

Incision

• A "fishmouth" (anterior and posterior flap) incision is standard
• The posterior flap is made 1-2 cm longer than the anterior flap to position the scar line anteriorly, away from the weight-bearing/prosthetic contact surface
• Incision corners curve proximally

Bone Transection

• A periosteal elevator clears the femur 2-3 cm proximal to the skin incision
• The femur is divided using a Gigli saw or oscillating/electric saw at the cleared level
• Sharp edges of the femoral stump are filed down with a rasp to avoid soft tissue injury

Vascular Control

• The superficial femoral/popliteal neurovascular bundle is suture-ligated
• The greater saphenous vein (located in superficial fascia medially) requires separate ligation
• If amputation is at or above the midthigh, identify the femoral artery and vein in the adductor canal

Nerve Handling - Sciatic Nerve

• The sciatic nerve is placed on tension, tied with absorbable suture, and sharply transected at that point - allowing it to retract proximally away from the wound to minimize neuroma formation at the scar line

Myodesis (Critical Step)

• Adductor myodesis is the most important muscle stabilization step
  • The major deforming forces on the stump are abduction and flexion
  • Transecting the adductor magnus without reattachment results in loss of 70% of adductor pull
  • Adductor myodesis maintains femoral adduction during stance phase, critical for optimal prosthetic function
  • It also eliminates the problem of adductor roll in the groin
• Muscle is reapproximated with absorbable sutures over the end of the femur to provide soft tissue coverage and a functional myodesis
• Miller's Review of Orthopaedics, 9th ed.; Fischer's Mastery of Surgery, 8th ed.

Compartment Anatomy at Amputation Level (Distal Thigh)

1. Anterior compartment - quadriceps femoris + sartorius, innervated by femoral nerve
2. Medial (adductor) compartment - adductor longus, brevis, magnus, gracilis, innervated by obturator nerve; contains the adductor canal
3. Posterior compartment - semimembranosus, semitendinosus, biceps femoris, innervated by sciatic nerve

Closure

• Fascia (anterior and posterior) closed with interrupted absorbable sutures
• Skin closed with vertical mattress interrupted permanent sutures (nylon) or deep dermal absorbable sutures + staples
• A drain may be placed over the myodesis before skin closure

Comparison with Other Amputation Levels

Postoperative Care

Dressings

• Elderly / dysvascular patients: soft dressing is adequate
• Young patients with nonischemic amputation: immediate postoperative rigid dressings applied, with early weight-bearing on a locked-knee pylon
• Elastic compression dressings at the AK level may be suspended about the contralateral iliac crest (rigid dressings are difficult to maintain at this level)

Preventing Complications

• Hip flexion contracture: mitigated with hip extension exercises and formal physical therapy; patient should not be allowed to sit with hip flexed for prolonged periods
• DVT/PE prophylaxis: subcutaneous heparin is essential - AK amputees are at significant risk in the early postoperative period
• Opiate analgesia: given regularly; phantom pain managed with gabapentin or amitriptyline
• Contralateral limb care: pressure ulcer on the remaining foot must be actively prevented as it delays mobilization

Weight Bearing Progression

1. Sutures/staples removed first - weight bearing best delayed until then for comfort
2. Ambulation with locked prosthetic knee and upper extremity support
3. Progress to unlocked knee with reduced upper extremity support

Complications

Early

• Hemorrhage - return to OR for hemostasis
• Hematoma - requires evacuation; risks secondary infection
• Infection - polymicrobial wound colonization; Staphylococci most prevalent; abscess must be drained + antibiotics
• Gas gangrene - can occur in mid-thigh stump from fecal contamination
• Wound dehiscence / flap gangrene - caused by ischemia; higher amputation may be required
• DVT / pulmonary embolism - requires prophylaxis

Late

• Phantom limb sensation - common; almost always resolves with time
• Phantom limb pain - gabapentin or amitriptyline; firm reassurance that resolution is expected
• Amputation neuroma - painful; results from failure to retract sciatic nerve sufficiently
• Bone spur - at the femoral transection site
• Stump ulceration - pressure from prosthesis or progressive ischemia
• Scar adherent to bone - painful; may require revision
• Sinus / osteitis / sequestrum - from unresolved infection

Long-term Statistics

• Amputation of the contralateral limb is necessary within 5 years in 30-50% of patients with dysvascular lower limb amputations
• 15% of below-knee amputations are converted to above-knee amputations at 5 years

Prosthetics

• A variety of prosthetic knee units are available:
  • Lightweight designs
  • Units accommodating constant or variable gait cadences
  • Units providing good stability during weight bearing
• The stump must be of sufficient length to accommodate the prosthetic knee - minimum ~12 cm above the knee joint
• Patients with dysvascular limbs are significantly less likely to achieve successful prosthetic ambulation compared to trauma/tumor amputees

Special Consideration: Knee Disarticulation vs. AK Amputation

• Preserves full femur length and patella
• Provides a long lever arm controlled by stronger muscles (line of transection is distal, through fascial tissue rather than thick muscle bellies)
• The bulbous end is now recognized as beneficial - allows a self-suspending prosthesis less prone to rotation
• For non-ambulatory elderly or bilateral amputees, the longer stump provides better counterweight to the torso, enabling better core stability
• Bailey and Love's Short Practice of Surgery, 28th ed.

• Sabiston Textbook of Surgery, The Biological Basis of Modern Surgical Practice
• Fischer's Mastery of Surgery, 8th ed.
• Campbell's Operative Orthopaedics, 15th ed. (2026)
• Miller's Review of Orthopaedics, 9th ed.
• Bailey and Love's Short Practice of Surgery, 28th ed.
• Current Surgical Therapy, 14th ed.
• Mulholland and Greenfield's Surgery, 7th ed.