Lateral unicompartmental replacement: a road less traveled.

Lateral unicompartmental replacement is performed less frequently than medial replacement and is technically more difficult. The ratio of medial to lateral arthroplasties is approximately 10:1. Differences in technique include the following: The patella is more vulnerable to impingement on the leading edge of the femoral component and must be carefully recessed. Because the wear pattern in lateral disease is more posterior than in medial disease, there often is residual cartilage on the distal femoral condyle. This is also the case when UKA is performed for the sequella of a lateral plateau fracture. To avoid this impingement, residual cartilage should probably be removed from the distal condyle before its resection and the femoral component should be undersized anteriorly. Initial tibial resection should be very conservative to avoid the need for very thick tibial components to restore alignment and stability. Err toward shifting the femoral component laterally and the tibial component medially to maximize mediolateral congruency. Consider a medial parapatellar approach (avoiding the anterior horn of the medial meniscus) to facilitate visibility and component alignment. Avoid excessive posterior tibial slope.