Dynamic Intraoperative ligament balancing for total knee arthroplasty

Complications after total knee arthroplasty, such as malalignment, instability, and excessive wear, have been attributed to poor soft tissue balance. Traditional instruments that assist in intraoperative soft tissue balancing rely on static measurements. We used a custom tibial trial, instrumented with force transducers, for dynamic measurement of soft tissue balance. Six cadaver knees and two patients were implanted with the trial tray along with a standard femoral component and a tibial insert. We recorded tibial forces during passive knee flexion, after the initial bone cuts were made, after soft tissue balancing, and after replacing the selected optimal insert with one that was 2 mm thicker. In all knees, substantial imbalance in tibial forces initially was recorded. Soft tissue balancing substantially reduced the imbalance. Although reasonable balance was achieved at 0 degrees and 90 degrees flexion, there was some measurable imbalance at flexion angles other than 0 degrees and 90 degrees. Increasing the thickness of the insert by 2 mm substantially increased net tibial forces. Inconsistent soft tissue balance may explain some of the wide variation in knee kinematics. Surgical navigation systems have reduced the variability in component alignment. An instrumented tibial trial can be a valuable adjunct to directly measure soft tissue balance.