Technical factors contributing to patellar instability in TKA

Patellar instability (PI) after total knee replacement (TKR) is one of the more frequent complications following the procedure. It is nearly completely avoidable with attention to detail during the procedure and particularly at the time of trial reduction. PI may be the result of malalignment of any of the components, not just malalignment of the patellar component. Most patients do not present for TKR with PI. Therefore if PI is evident at the time of tiral reduction, a check for component malalignment should ALWAYS be carried out, and not an immediate default to lateral release. Preoperative PI increases the risk of postoperative PI. The surgeon must be prepared to do whatever is necessary to be certain that there is no PI when the surgery is finished. This can include lateral release, but in some cases, medialization of the tibial tubercle may be necessary. When PI is encountered in follow-up after TKR, a careful evaluation of component malalignment is essential, including rotational malalignment of the femoral or tibial components that might not be obvious of standard radiographs.