COMPUTER ASSISTED LIGAMENT BALANCING IN TOTAL KNEE REPLACEMENT

Abstract

The ligament balancing technique involves precise measurement and equalisation of flexion and extension gaps. A force tension distractor that has separate arms for the medial and lateral joint compartments was used. We describe our experience of 40 total knee replacements (TKR) using this technique.

We undertook a prospective randomised trial using computer assisted navigation in TKRs applying two different soft tissue balancing techniques. The aim was to see how balancing techniques help us achieve a rectangular flexion extension gap. The 40 TKR that underwent the ligament balancing procedure were part of this trial. The distractor used was derived from the Freeman-Swanson knee instrumentation which measures the gap and tension in the medial and lateral compartments. The options to make the gap rectangular were: 1. adjustment of femoral cut by change in external rotation (for the flexion gap); 2. soft- tissue release or 3. a combination of both. Using computer assisted navigation it was possible to perform real time motion analysis during surgery.

We found that three degrees of external rotation for the femoral component was adhered to in only 16 out of 40 knees. The remaining 60% had external rotation of femoral component varying between two and eight degrees. No maltracking of the patella resulted in any of the TKR with increased rotation of the femoral component. The axis of movement was plotted on a graph at the end of the surgery by passive extension to flexion to which the operating surgeon was blinded.

Varying external rotation of femoral component might be an option in balancing difficult knees. Computer navigation enables precise tailoring of bony resection to suit different deformities.