Below-Knee (Transtibial) Amputation

Definition & Overview

Indications

• Peripheral arterial disease (PAD) with non-viable foot and no revascularization options
• Diabetic foot: major infection, significant tissue loss, or non-healing ulcers
• Trauma
• Malignancy (tumor with clear margins)
• Congenital deformities
• Irreversible ischemia/gangrene of the foot

• Knee flexion contracture (>20 degrees) - makes prosthetic use impractical
• Absent femoral pulse (above-knee amputation is more appropriate)
• Insufficient viable anterior/posterior flap tissue
• Ankle-brachial index <0.5 (poor healing likelihood)

Level of Amputation

• The tibia is typically transected 10-15 cm distal to the tibial tuberosity
• The fibula is transected 2 cm proximal to the tibial level to avoid a prominent distal fibula in the prosthetic socket

Surgical Technique

Flap Options

• Posterior skin/muscle is supplied by sural arteries, which arise proximal to the knee - relatively spared in tibial artery disease
• Highest incidence of primary wound healing

Step-by-Step (Long Posterior Flap - Greenfield/Sabiston)

1. Mark the skin - Anterior incision at level of tibial transection (2/3 leg circumference); longitudinal extensions (1/3 circumference each side); posterior incision connects them with curved transitions
2. Deepen incision through fascia; ligate the great and small saphenous veins
3. Anterior compartment - Deepen through periosteum; divide anterior compartment muscles at incision level; identify and suture-ligate the anterior tibial neurovascular bundle; clear periosteum circumferentially
4. Tibial transection - Cut tibia with oscillating/reciprocating saw; bevel the anterior surface at 45 degrees to prevent skin erosion from the sharp edge; tibia transected 1 fingerbreadth proximal to the skin incision
5. Fibula - Dissect out and transect 2 cm proximal to tibial cut with bone cutters
6. Posterior dissection - Retract tibia anteriorly; divide posterior musculature along longitudinal flap edges (careful to protect posterior flap skin edges); identify, ligate and divide posterior tibial and peroneal neurovascular bundles
7. Nerves - The tibial nerve and peroneal nerve are ligated with absorbable suture and sharply transected as proximally as possible to allow retraction away from the wound (prevents neuroma at scar)
8. Hemostasis - Manual compression; ligate remaining vessels; no bone wax
9. Posterior flap - Rotate anteriorly; debulk excess muscle to allow tension-free closure; preserve gastrocnemius muscle and fascia
10. Closure - Secure deep posterior musculature over the tibial end (myodesis); approximate posterior fascia to anterior fascia with absorbable sutures; close subcutaneous tissue and skin (vertical mattress or staples); optional closed-suction drain

Key Anatomical Points (Fischer's Mastery)

• The anteromedial surface of the tibia lies just deep to superficial fascia - no muscle division needed to expose it
• Anterior tibial vessels and deep peroneal nerve lie in the anterior compartment between tibialis anterior and EDL
• Common peroneal nerve wraps around the fibular neck - must be divided proximal to its bifurcation
• Posterior tibial and peroneal vessels lie between superficial and deep posterior compartments (deep to soleus, superficial to tibialis posterior)
• Great saphenous vein + saphenous nerve are in the superficial fascia just posterior to the medial tibial border

Nonischemic vs. Ischemic Limbs (Campbell's 2026)

Postoperative Management

• Analgesia: Regular opioids; consider preoperative/perioperative regional nerve block (reduces phantom pain)
• Two-stage approach for septic foot: initial guillotine amputation as distal as possible, then formal BKA once infection cleared and patient stabilized
• Stump dressing: Rigid dressings preferred in early postoperative period (reduces edema, protects residual limb, prepares for prosthesis)
• Early prosthetic fitting: Can begin 5-21 days postoperatively if the residual limb can transfer load and patient has adequate physical reserve
• Prevent contracture: Physiotherapy started early; avoid prolonged hip/knee flexion
• Contralateral limb care: Pressure ulcer prevention is critical - a wound on the remaining foot delays mobilization
• Nutritional optimization: Albumin ≥3 g/dL, lymphocyte count ≥1500/mL required for adequate wound healing
• TcPO2: <20 mmHg predicts wound healing failure

Predicting Healing

Outcomes & Energy Expenditure

• Ambulation rates (with or without assistance): up to 65% of BKA patients
• Energy expenditure for walking: BKA increases oxygen consumption by 40-50% above normal (vs. 90-100% for above-knee amputation)
• BKA patients are more likely to successfully use a prosthesis than transfemoral amputees
• More proximal amputation = decline in physical function and quality of life
• Patients with dysvascular limbs or on dialysis have lower prosthetic success rates

Complications

• Wound dehiscence / non-healing (most common in vascular disease - may require revision to AKA)
• Stump infection / surgical site infection
• Hematoma (prevented by closed-suction drain)
• Neuroma (minimized by high nerve transection and proximal retraction)
• Phantom limb pain / sensation
• Flexion contracture at the knee (prevented by early physio)
• Skin breakdown over bony prominences with prosthesis use
• Patellar problems (patellar dislocation, patella alta) - especially in younger amputees using patellar tendon-bearing sockets

Prosthetic Fitting

• Minimum stump length: 8 cm below knee (preferably 10-12 cm) for adequate leverage
• Suction-suspension prostheses are available when stump shape is good
• Contemporary liner and ankle-foot storage systems now accommodate longer residual limbs
• Shorter stumps (<8.8 cm) may require total-contact socket fitting with fibular head retention for better purchase

• Fischer's Mastery of Surgery, 8th ed., pp. 6659-6660
• Mulholland and Greenfield's Surgery, 7th ed., p. 5001-5002
• Campbell's Operative Orthopaedics, 15th ed. 2026, pp. 878-879
• Sabiston Textbook of Surgery, p. 1516-1520
• Miller's Review of Orthopaedics, 9th ed., p. 2503-2509
• Bailey and Love's Short Practice of Surgery, 28th ed., p. 8000-8041