Below-knee amputation (BKA)

Common indications

• Severe peripheral arterial disease with non-salvageable foot
• Major diabetic foot infection or gangrene
• Extensive trauma or burns
• Tumor or irreversible tissue loss
• Failed limb-salvage procedures

Basic operative principles

• The surgeon plans skin and muscle flaps that have adequate blood supply.
• The tibia and fibula are divided, with the tibia shaped to avoid a prominent sharp edge.
• Blood vessels are ligated and nerves divided sufficiently proximally to reduce painful neuroma risk.
• Muscle is secured over the bone and the flap is closed to form a padded residual limb for later prosthetic fitting.

After surgery

1. Pain management, including treatment of phantom-limb pain if it occurs.
2. Monitoring wound healing, bleeding, infection, and stump blood supply.
3. Preventing knee-flexion contracture through correct positioning and physiotherapy.
4. Residual-limb shaping with dressings or a rigid removable protector as advised.
5. Early rehabilitation, strengthening, balance training, and prosthetic assessment.

Important complications

• Delayed healing or wound infection
• Skin breakdown or poor stump perfusion
• Knee-flexion contracture
• Phantom sensation or phantom pain
• Neuroma-related stump pain
• Venous thromboembolism
• Need for revision to a higher level if healing fails

Steps of below-knee amputation

1. Preoperative assessment and planning
   • Confirm that the limb is non-salvageable and assess vascular supply.
   • Select the lowest level likely to heal while preserving sufficient tibial length for prosthetic use.
   • Mark the tibial tuberosity, knee joint line, intended bone-cut level, and skin flaps.
   • Give anesthesia, antibiotics when indicated, and position the patient supine.
2. Apply tourniquet and prepare the limb
   • Prep and drape the limb.
   • A thigh tourniquet may be used if appropriate, but use depends on vascular status and operative judgment.
3. Mark and create skin flaps
   • The tibia is generally divided about 12 to 15 cm distal to the tibial tuberosity.
   • Create a shorter anterior skin incision and a longer posterior musculocutaneous flap.
   • The posterior flap provides well-padded coverage over the bone ends.
4. Divide anterior and lateral compartment muscles
   • Incise skin and fascia.
   • Divide muscles of the anterior and lateral compartments at an appropriate level.
   • Identify, ligate, and divide anterior tibial vessels as needed.
5. Expose and divide the tibia
   • Elevate periosteum sufficiently to permit bone division.
   • Divide the tibia, usually slightly proximal to the skin edge.
   • Bevel or round the anterior tibial edge to prevent a sharp bony prominence and later pressure injury.
6. Divide the fibula
   • Expose and transect the fibula about 1 to 2 cm proximal to the tibial cut.
   • Smooth the bone end as required.
7. Control vessels and manage nerves
   • Securely ligate major vessels.
   • Gently draw down major nerves, divide them sharply at a proximal level, and allow them to retract into soft tissue. This aims to reduce painful neuroma formation.
8. Complete the posterior flap
   • Release posterior compartment muscles from the tibia and fibula while preserving adequate gastrocnemius-soleus tissue for padding.
   • Debulk excessive muscle only if needed to create a well-contoured residual limb.
9. Myoplasty or myodesis
   • Advance posterior muscle and fascia anteriorly over the bone ends.
   • Secure the flap to anterior fascia or bone, according to the surgeon's technique, to provide stable soft-tissue padding.
10. Hemostasis, irrigation, and closure

• Release the tourniquet if used and obtain meticulous hemostasis.
• Irrigate the wound.
• Insert a drain selectively.
• Close fascia, subcutaneous tissue, and skin without tension.

1. Dress and protect the stump

• Apply a sterile compression dressing, rigid dressing, or removable rigid protector as appropriate.
• Keep the knee extended and begin early rehabilitation to avoid knee-flexion contracture.

In a grossly infected or septic foot

• First: distal guillotine amputation to control sepsis.
• Later: formal below-knee stump formation after stabilization and confirmation of viable tissue.

Long posterior flap technique for below-knee amputation

Step-by-step

1. Assess the level and flap viability
   • Confirm that a below-knee level is likely to heal.
   • Examine the anterior and posterior skin, calf muscle, and arterial inflow.
   • In severe infection or wet gangrene, a staged guillotine amputation followed by delayed formal stump construction may be safer.
2. Position and prepare
   • Place the patient supine.
   • Administer general or regional anesthesia.
   • Prep and drape the full leg, with a tourniquet used selectively.
   • Mark the tibial tuberosity, knee joint line, proposed tibial division level, and planned flap outline.
3. Plan the incision
   • The tibial cut is commonly planned about 12 to 15 cm below the tibial tuberosity.
   • Mark a relatively short anterior flap and a longer posterior musculocutaneous flap extending toward the calf/ankle.
   • Curve the medial and lateral incision limbs toward the malleoli.
   • The purpose of the longer posterior flap is to bring vascularized skin, fascia, gastrocnemius, and soleus tissue over the anterior tibial end without tension.
4. Incise skin and deep fascia
   • Incise along the marked anterior, medial, and lateral lines down to deep fascia.
   • Control bleeding as dissection proceeds.
   • Divide the fascia and anterior/lateral compartment muscles with electrocautery at the planned level.
5. Control anterior neurovascular structures
   • Identify and securely ligate the relevant vessels.
   • Handle the nerves gently. The tibial and peroneal nerves are placed under slight traction, divided sharply at a sufficiently proximal level, and allowed to retract into soft tissue. This reduces the risk of a painful terminal neuroma at the scar or bone end.
6. Expose and divide the tibia
   • Elevate periosteum enough to expose the tibia while preserving suitable soft tissue.
   • Divide the tibia approximately 2 cm proximal to the anterior skin edge.
   • Bevel and smooth the anterior tibial crest so it does not create a sharp pressure point beneath the future prosthesis.
7. Expose and divide the fibula
   • Dissect out the fibula.
   • Divide it approximately 2 cm proximal to the tibial cut, avoiding a prominent lateral bony end.
   • Smooth irregular bone edges.
8. Fashion the posterior flap
   • Release the posterior compartment from the tibia and fibula using an amputation knife or cautery.
   • Preserve adequate gastrocnemius muscle and fascia for cushioning.
   • Remove only enough excess posterior muscle to prevent a bulky, poorly shaped stump.
   • Preserve flap perfusion and avoid excessive tension or aggressive thinning.
9. Achieve hemostasis
   • Identify and ligate vessels individually.
   • Irrigate the operative field.
   • If a tourniquet was used, release it and obtain meticulous hemostasis before closure.
   • Bone wax is generally avoided in this setting because it may interfere with healing or serve as a foreign body.
10. Bring the posterior flap anteriorly

• Advance the posterior musculofascial flap over the tibial and fibular ends.
• Suture the posterior flap fascia to the anterior fascia using interrupted absorbable sutures.
• This is a myoplasty: it creates stable soft-tissue padding over bone and avoids an adherent, tender scar directly over the tibia.

1. Close the wound

• Ensure skin closure is tension-free and the scar is positioned away from the main distal pressure-bearing area where possible.
• Close deep dermis with absorbable sutures, then use staples or mattress sutures for skin according to surgeon preference.
• A drain may be used selectively.

1. Dress and rehabilitate

• Apply a sterile compression dressing or rigid removable dressing.
• Maintain the knee in extension, avoiding prolonged pillow support beneath the stump.
• Begin early physiotherapy, edema control, contracture prevention, and later prosthetic rehabilitation.

Why use a long posterior flap?

Key technical points to remember

• Preserve the knee joint and adequate tibial length, but do not choose a level unlikely to heal.
• Tibia: cut about 12 to 15 cm below tibial tuberosity and bevel the anterior edge.
• Fibula: cut about 2 cm shorter than the tibia.
• Divide nerves proximally and sharply.
• Bring posterior gastrocnemius-soleus tissue forward for durable stump padding.
• Close only after adequate blood supply, hemostasis, and a tension-free flap are confirmed.