Below-Knee (Transtibial) Amputation

Definition & Overview

Indications

• Severe trauma or crush injury
• Malignancy (soft tissue or bone sarcoma)
• Severe infection / necrotizing fasciitis / gas gangrene
• Congenital limb deficiency
• Chronic non-healing wounds unresponsive to revascularization

Choosing BKA vs. AKA

Level of Amputation

• Ideal tibial length: 12.5 to 17.5 cm from the medial knee joint line (rule of thumb: 2.5 cm per 30 cm of body height)
• Standard level: tibia transected ~10 cm below the tibial tuberosity
• Fibula: cut 1-2 cm shorter than the tibia
• Distal third of the leg is suboptimal - poor vascularity, slower healing, limited soft tissue
• In ischemic limbs, amputation is customarily at a higher level (10-12.5 cm distal to the joint line)

Surgical Techniques

1. Long Posterior Flap (Burgess Technique) - Most Common

• Anterior incision: 1 cm distal to the proposed tibial transection level, with a length equal to two-thirds of the leg circumference at that level
• Medial and lateral longitudinal limbs: each one-third of the circumference (~9-12 cm)
• The posterior flap must be generous - excess is trimmed at closure

1. Anterior compartment muscles divided at skin incision level
2. Anterior tibial neurovascular bundle - identified and suture-ligated
3. Tibia cleared of periosteum; transected with oscillating/Gigli saw; anterior cortex beveled at 45° to prevent pressure necrosis
4. Fibula cleared and transected 2 cm proximal to tibial cut
5. Posterior tibial and peroneal neurovascular bundles - suture-ligated
6. Nerves (posterior tibial, common peroneal, deep peroneal, sural) - gently retracted distally, sharply divided, allowed to retract proximally to prevent neuroma formation
7. Posterior flap rotated anteriorly; muscle debulked as needed
8. Deep posterior musculature secured over tibial end (myodesis to periosteum)
9. Gastrocnemius fascia approximated to anterior fascia - absorbable suture
10. Skin closed with interrupted nylon or staples

2. Skew Flap (Robinson/Jain Technique)

• A fishmouth incision is made at 10-25 cm below the joint line (2-2.5 cm lateral to tibial crest as the flap junction point)
• Creates anterolateral and posteromedial flaps of equal quarter-circumference length
• The posterior gastrocnemius-soleus complex is brought anteriorly and secured to anterior periosteum
• The suture line lies off the tibial crest - reducing pressure from prosthetic socket

3. Equal Anterior and Posterior Flaps (Classic)

4. Ertl (Osteomyoplastic) Amputation

• A bone bridge is created between tibia and fibula using a fibular autograft strut
• Notches cut in both bones; strut secured with heavy sutures
• Advantages: more stable end-bearing construct, decreased tibiofibular joint instability, better load transfer

• Tourniquet traditionally avoided (though recent RCTs show it may be safe)
• Tension myodesis and osteomyoplasty contraindicated in ischemic limbs - compresses remaining blood supply
• Skew or posterior flaps favored over anterior flaps

Neurovascular Management

Postoperative Management

• Rigid dressing or posterior splint - prevents knee flexion contracture (major complication)
• Closed-suction drain - optional, at surgeon's discretion to prevent hematoma
• Skin closure kept for at least 3 weeks until healed
• Stump shrinker applied after wound healing to shape residual limb for prosthetic fitting
• Early prosthetic fitting: 5 to 21 days postoperatively if residual limb can transfer load and patient has adequate physiologic reserve
• Formal inpatient rehabilitation is brief; most prosthetic training is outpatient

Rehabilitation

• Requires functional quadriceps - stumps lacking quadriceps function are not useful for prosthetic ambulation
• Physiatrist + physical therapist guide progression: rigid dressing → temporary prosthesis → permanent prosthesis (process takes several months)
• Endoskeletal (pylon) prosthetic designs preferred - easier to modify
• Goals: return to prior occupation, hobbies, education (with social work + vocational counseling support)
• Rehabilitation in nonischemic limbs is far more aggressive and successful due to younger, healthier population

Complications

Key Points Summary

• BKA preserves the knee joint and dramatically reduces the energy cost of ambulation compared to AKA
• The long posterior flap (Burgess) is the standard technique for vascular patients
• Ideal tibial length: 12.5-17.5 cm; minimum functional length ~8.8 cm
• Fibula cut 2 cm proximal to tibia; anterior tibial cortex beveled at 45°
• All nerves divided under traction and allowed to retract - prevents neuroma
• Tension myodesis is contraindicated in ischemic limbs
• Knee flexion contracture and wound breakdown are the two major preventable complications