Below-Knee Amputation (Transtibial)

The operation in one line. A below-knee (transtibial) amputation divides the tibia and fibula roughly a hand's breadth below the knee, covers the bone end with a cushioned gastrocnemius-based muscle flap, and preserves the knee joint - the single most important determinant of efficient prosthetic walking. The Big Four indications ("Dead, Dangerous, Damaged, Damn nuisance").

Why preserving the knee matters. Whenever the limb can heal at a transtibial level, a BKA is preferred over an AKA: - Energy cost of gait - transtibial amputees ambulate with roughly a 25% increase in energy expenditure above normal, whereas transfemoral amputees require around 65% more. The knee joint is the single biggest determinant of efficient prosthetic walking.

• Prosthetic rehabilitation - preserving the anatomical knee dramatically improves the proportion of patients who become independent prosthetic walkers, particularly the frail, elderly and dysvascular in whom every extra metabolic demand matters.
• Functional independence - lower fall risk, better balance, and a higher likelihood of returning to community ambulation than with an above-knee amputation.
• The trade-off - this benefit only holds if the BKA level will heal. A non-healing BKA that converts to an AKA is worse than a primary AKA, so level selection is the critical judgement. Level selection. The level is dictated by where the flap will heal, not by cosmetic length - but a well-shaped stump is the aim wherever perfusion allows. - Ideal length - about 12-15cm of tibia from the tibial tuberosity, classically a hand's breadth below the tuberosity (a rough guide is about 2.5cm of bone per 30cm of body height).
• Minimum functional length - a stump shorter than about 8cm of tibia below the joint line gives a poor lever arm, is hard to fit and is prone to flexion contracture; an extremely short stump may be no better functionally than a knee disarticulation.
• Maximum length - avoid an over-long distal stump, because soft-tissue cover and perfusion are poorer in the lower third of the leg and the muscle bulk for padding is thinner.
• Perfusion overrides geometry - in the dysvascular limb the level is ultimately set by where the flap will heal. Contraindications to a transtibial level. - Inadequate perfusion at the proposed level (very low TcPO2, absent popliteal pulse with unreconstructable disease).
• A knee flexion contracture or a non-functional knee that would preclude prosthetic use.
• Extensive proximal soft-tissue loss, sepsis or tumour reaching the upper calf.
• A non-ambulatory patient in whom a higher, more reliably healing level may be more pragmatic (individualised). Pre-operative optimisation. Wound healing in the dysvascular and diabetic limb is governed by perfusion and nutrition, so optimise before committing to a level: - Vascular assessment and intervention - confirm inflow and decide whether revascularisation could lower the amputation level or improve healing.
• Sepsis control - in wet gangrene or ascending infection, consider a staged guillotine amputation first to control sepsis before definitive flap-based closure.
• Metabolic and nutritional optimisation - tight glycaemic control, correct anaemia, and address malnutrition (serum albumin and total lymphocyte count are practical, validated healing predictors).
• Medical and anaesthetic work-up - these patients are frequently elderly with significant cardiac, renal and respiratory comorbidity; multidisciplinary peri-operative care reduces mortality. Consent specifically for wound failure and possible conversion to a higher level, stump or phantom limb pain, neuroma, infection, knee flexion contracture, and the realistic prosthetic and mobility outlook given the patient's comorbidity and the contralateral limb.

The goal is to divide the tibia and fibula at a level that will heal, cover the bevelled bone end with a cushioned, stable gastrocnemius-based flap, handle each nerve and vessel deliberately, and close without tension so the scar lies off the weight-bearing bone-end - then protect it all in a rigid dressing with the knee in extension. The exposure is laid out as the opening steps below. The images below illustrate one specialised transtibial technique - a sensate calcaneal (plantar) flap transferred onto the tibial end to permit terminal weight-bearing - shown intra-operatively and through to long-term follow-up.

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Immediate post-operative phase (0-2 weeks) - Rigid dressing (or rigid removable dressing) with the knee in full extension to control oedema, protect the stump and prevent flexion contracture.

• Elevate the residual limb early but avoid a pillow under the knee (it promotes contracture).
• Remove the suction drain at about 24-48 hours; monitor the flap for perfusion and haematoma.
• Multimodal analgesia with attention to phantom and residual limb pain: regional catheters, gabapentinoids or amitriptyline, paracetamol or NSAIDs and short-term opioids; introduce mirror therapy early.
• Encourage knee extension and prone-lying periods; begin gentle hip and knee range of motion and bed mobility. Intermediate phase (2-6 weeks) - Suture or clip removal at about 2-3 weeks (later in dysvascular and diabetic patients who heal more slowly).
• Progress to a stump shrinker or elastic compression once the wound is sound, to shape the stump for prosthetic casting; continue oedema control and desensitisation.
• Early walking aids (such as a pneumatic post-amputation mobility aid) allow trial weight-bearing and gait re-education before the definitive prosthesis; Burgess-style early or immediate postsurgical prosthetic fitting accelerates rehabilitation in suitable patients.
• Multidisciplinary care: vascular and diabetic optimisation, podiatry, protection of the contralateral limb (high risk of subsequent amputation), wound care and dietitian input. Rehabilitation (6 weeks to 6-12 months) - Cast for a definitive socket once the stump is mature and stable; progressive prosthetic gait training toward independent community ambulation, leveraging the preserved knee and the favourable ~25% energy cost of transtibial gait.
• Counsel realistically - outcomes depend on age, cardiorespiratory reserve, comorbidity and the contralateral limb; set expectations honestly and individualise goals (community versus household ambulation versus wheelchair independence). Mortality after major lower-limb amputation for vascular disease is substantial.
• Reinforce knee extension at every stage - the flexion contracture is the most preventable cause of a functionally useless transtibial stump. Watch also for late neuroma, stump breakdown over a prominent bone end, and the contralateral limb. Warning signs requiring urgent review: increasing pain, swelling, erythema or discharge (infection or haematoma); new flap discolouration or dehiscence; a developing knee flexion contracture compromising prosthetic fitting.

The non-healing or failing stump. Re-assess perfusion (consider angiography or revascularisation if not already optimised), nutrition and infection. Minor distal margin necrosis can be managed conservatively, but a substantially non-viable flap is best dealt with by timely revision rather than repeated futile debridements. Conversion to an AKA is a salvage decision - explain that the rehabilitation trade-off (higher energy cost) is the price of a reliably healing wound. Staged ("guillotine") amputation. In severe ascending infection or wet gangrene, a rapid open guillotine amputation through healthy tissue controls sepsis; definitive flap-based BKA closure is performed once infection is controlled, reducing the risk of closing over infected tissue.

Surgical anatomy that governs the operation. At the level of section the leg holds four compartments, and each must be addressed deliberately: - Anterior compartment - tibialis anterior, EHL, EDL and fibularis tertius, carrying the anterior tibial artery and deep peroneal nerve on the interosseous membrane; these are divided and ligated as the anterior flap and muscles are taken.

• Lateral compartment - fibularis longus and brevis, with the superficial peroneal nerve that emerges through the deep fascia in the lower leg.
• Superficial posterior compartment - gastrocnemius and soleus, the muscle bulk that forms the durable long posterior myocutaneous flap with its robust overlying calf skin.
• Deep posterior compartment - tibialis posterior, FDL and FHL, carrying the posterior tibial artery and nerve and the peroneal artery, the principal pedicles to ligate. The bones. The tibia is triangular with a subcutaneous antero-medial surface; the sharp anterior crest must be bevelled 45-60 degrees with all edges smoothed. The fibula is divided 1-2cm shorter than the tibia so it does not become a distal prominence, and its lateral edge is bevelled. Nerves to address. The tibial nerve is the largest; it lies deep posteriorly with an accompanying artery (a sizeable epineurial vessel) that must be ligated to prevent a stump haematoma, and is treated with gentle traction neurectomy. The common peroneal nerve is addressed proximally - vulnerable as it winds round the fibular neck, so the traction neurectomy is kept high to keep the neuroma away from the lateral stump. The sural nerve runs subcutaneous in the posterior flap with the short saphenous vein, and the saphenous nerve medially with the long saphenous vein. Blood supply relevant to the flaps. The long posterior flap is perfused chiefly by the posterior tibial and peroneal arteries via the sural arteries to gastrocnemius, giving it reliable perfusion even in dysvascular limbs. The skew flap is based on the perforating or angiosomal supply to skin, with the sagittal flaps positioned to optimise cutaneous perfusion. The angiosome concept - matching the retained flap to the dominant patent inflow (for example the posterior tibial) - supports healing in ischaemic limbs. Surface anatomy and landmarks for marking. The tibial tuberosity is the primary reference for level (the cut sits a hand's breadth distal to it). The anterior tibial crest is subcutaneous and palpable - the line to bevel, and where skin breakdown occurs if a spike is left. The fibular head and neck mark the common peroneal nerve proximally. The posterior calf bulk - the gastrocnemius-soleus mass - becomes the durable posterior flap; mark its length against the AP diameter of the leg at the level of section. Functional anatomy for the prosthesis. The patellar tendon, tibial flares and gastrocnemius pad are the weight-tolerant areas a patellar-tendon-bearing or total-surface-bearing socket loads, so preserving padded, mobile-free soft tissue over the bone end is essential. A flexion contracture at the knee changes socket alignment and the moment arm, which is why maintaining full passive extension is both an anatomical and a rehabilitation priority. Wound-healing predictors - why level selection fails or succeeds. Arterial perfusion (a palpable popliteal pulse, ankle-brachial index, toe pressures) reflects inflow to the flap; the long posterior flap's gastrocnemius supply makes it relatively forgiving in ischaemia. Transcutaneous oxygen pressure measured at the proposed level - values above about 30-40 mmHg predict primary healing, while very low values predict failure. Nutrition and immunocompetence matter: low serum albumin and a depressed total lymphocyte count are associated with non-healing and amputation in diabetic foot disease. Uncontrolled diabetes and active infection both impair healing and should be addressed before definitive closure.

Rigid dressings and early rehabilitation. Burgess popularised the immediate postoperative rigid dressing and immediate or early postsurgical prosthetic fitting, allowing earlier mobilisation and oedema control. Rigid removable dressings protect the stump, control oedema, may speed healing and reduce knee flexion contracture compared with soft dressings, and facilitate progression to weight-bearing. The evidence base. Burgess (1971) established the long posterior myocutaneous flap with myoplasty for peripheral vascular insufficiency, the workhorse for dysvascular limbs; its gastrocnemius-based blood supply underpins its reliability in critical ischaemia. Robinson (1982) introduced the skew flap based on the cutaneous perforator supply to produce a cylindrical, well-perfused stump. The multicentre randomised trial by Ruckley (1991) randomised 191 patients across 11 centres and found no significant difference in primary healing between the skew and long posterior flaps. Wolthuis (2006) challenged the dogma that a tourniquet is contraindicated in dysvascular amputation, but as a non-randomised cohort the evidence is suggestive rather than definitive. Waters (1976) established the objective basis for preserving the knee: walking performance and oxygen cost were significantly better the lower (more distal) the amputation level.

Further reading and source references 1. Burgess EM, Romano RL, Zettl JH, Schrock RD Jr. Amputations of the leg for peripheral vascular insufficiency. J Bone Joint Surg Am. 1971;53(5):874-890. Classic description of the long posterior flap transtibial amputation with myoplasty in dysvascular limbs. 2. Burgess EM. Amputations below the knee. Artif Limbs. 1969;13(1):1-12. Foundational account of below-knee amputation principles and stump management. 3. Romano RL, Burgess EM. Level selection in lower extremity amputations. Clin Orthop Relat Res. 1971;74:177-184. Principles of choosing the amputation level to balance healing and prosthetic function. 4. Robinson KP, Hoile R, Coddington T. Skew flap myoplastic below-knee amputation: a preliminary report. Br J Surg. 1982;69(9):554-557. Original description of the skew-flap technique based on cutaneous perforator supply. 5. Robinson KP. Skew-flap below-knee amputation. Ann R Coll Surg Engl. 1991;73(3):155-157. Refinement and rationale of the skew-flap design for a cylindrical, well-perfused stump. 6. Ruckley CV, Stonebridge PA, Prescott RJ. Skewflap versus long posterior flap in below-knee amputations: multicenter trial. J Vasc Surg. 1991;13(3):423-427. Multicentre RCT showing no significant difference in primary stump healing between the two flaps. 7. Wolthuis AM, Whitehead E, Ridler BM, Cowan AR, Campbell WB, Thompson JF. Use of a pneumatic tourniquet improves outcome following trans-tibial amputation. Eur J Vasc Endovasc Surg. 2006;31(6):642-645. Reduced blood loss and transfusion with tourniquet, without increased wound failure. 8. Burgess EM, Romano RL. The management of lower extremity amputees using immediate postsurgical prostheses. Clin Orthop Relat Res. 1968;57:137-146. Introduction of the rigid dressing and immediate postsurgical prosthetic fitting concept. 9. Holloway GA Jr, Burgess EM. Cutaneous blood flow and its relation to healing of below knee amputation. Surg Gynecol Obstet. 1978;146(5):750-756. Early evidence linking skin perfusion to transtibial wound healing and level selection. 10. Brookes JDL, Jaya JS, Tran H, et al. Broad-Ranging Nutritional Deficiencies Predict Amputation in Diabetic Foot Ulcers. Int J Low Extrem Wounds. 2020;19(1):27-33. Demonstrates nutritional status (including albumin) as a predictor of amputation and healing. 11. Waters RL, Perry J, Antonelli D, Hislop H. Energy cost of walking of amputees: the influence of level of amputation. J Bone Joint Surg Am. 1976;58(1):42-46. Prosthetic walking performance and oxygen cost are progressively better the lower (more distal) the amputation level. 12. Ameli FM, Byrne P, Provan JL. Selection of amputation level and prediction of healing using transcutaneous tissue oxygen tension (PtcO2). J Cardiovasc Surg (Torino). 1989;30(2):220-224. Prospective study supporting transcutaneous oxygen tension as a valid predictor of primary amputation healing.