Through Knee Amputation with foot fillet sole flap cover
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Through Knee Amputation (TKA) is not routinely performed in either the UK or US with both countries reporting an incidence between 2%-5% of all lower limb amputations. Through knee amputation is more commonly described in relation to trauma and malignancy. However, most patients requiring amputation have either peripheral vascular disease and/or diabetes. Where possible a Below Knee Amputation (BKA) is favoured because of the increased energy required to ambulate with either a TKA or Above Knee Amputation (AKA), and the walking speeds are reduced due to the heavier prosthesis containing 2 joints i.e. a knee and ankle.
Through knee amputation has several advantages but concerns remain regarding poor wound healing, failure to rehabilitate, and revision to an AKA, so in a population with multiple co-morbidities, some surgeons prefer one definitive operation and perform an AKA.
Advantages of the TKA are that it has functional superiority compared to an AKA in both ambulatory and non-ambulatory patients. The longer lever arm makes walking less onerous and uses less energy. Retention of the adductor muscles is better for proprioception and aids the limbs overall power. The larger weightbearing surface area reduces the risk of prosthesis related pressure sores, and the intact femur is end-weightbearing and makes transfers easier in non-ambulant patients. In the sitting position, the additional weight of the whole femur helps with counter-balance and compared to the AKA, the prosthesis fitting is simplified without the need for a belt or strapping. Compared to the BKA patient that is non-ambulant, a TKA is preferable because the BKA patients can develop a flexion contracture of the knee and develop stump pressure sores on the posterior aspect.
Disadvantages are primarily related to poor wound healing in the peripheral vascular disease / diabetic population, where surgeons then opt to perform an AKA. The other issue is the level of the prosthetic knee joint which does not align with the normal native joint, and when sitting can have an abnormal cosmetic appearance. An AKA also has space within the prosthesis to accommodate a shock absorbing mechanism.
A common FRCS exam question is regarding the amount of energy required for ambulation for patients with a BKA or AKA.
- A BKA typically uses 40% more energy than a non-amputee.
- An AKA typically uses 65% more energy than a non-amputee.
So on average, an AKA uses approximately 50% more energy to ambulate than a BKA.
- A TKA therefore uses between 40%-65% more energy than a non-amputee.
Of note, the amount of energy used by a BKA varies depending on the length of the tibial segment.
Through knee amputation has been described with a range of techniques (please see the Indications section for a full description). These are called:
In this technique we use the classical technique to perform a TKA for a young male patient with an infected tibial plateau fracture with articular surface bone loss. Unfortunately this patient sustained a Schatzker 5 tibial plataeu fracture and compartment syndrome requiring fasciotomy. Despite spanning external fixation and allowing the soft tissues to settle, he underwent open reduction internal fixation with local flap cover but this became infected. Following serial debridements he was counselled on the reconstructive options with a TKA being one option.
OrthOracle readers will also find the following instructional operative techniques of interest:
The following technique was a combined OrthoPlastic procedure with Miss Deborah Foong, Consultant Plastic Surgeon, FRCS (Plast).
Author: Ross Fawdington FRCS (Tr & Orth)
Institution: The Queen Elisabeth Hospital, Birmingham, UK.
Clinicians should seek clarification on whether any implant demonstrated is licensed for use in their own country.