Making your next unicompartmental knee arthroplasty last: three keys to success

Alignment, ligament balance, and implant fixation are essential in unicompartmental knee arthroplasty. Adequate exposure allows assessment of the opposite compartment, trimming of medial femoral and tibial osteophytes, and a thorough notchplasty. Intramedullary instruments provide accurate and reproducible alignment of the implants in extension, and the anteroposterior axis offers the best landmark for varus-valgus alignment in flexion and also centers the femoral component on the surface of the tibial component. Complete osteophyte excision frees the collateral and cruciate ligaments and minimizes ligament balancing. The implants should allow 1 to 3 mm of laxity in flexion and extension, and if more laxity is required, reresection should be done posteriorly or distally. Fixation depends on excellent bone stock along with precise alignment, and avoiding tibial overresection ensures adequate support of the implant.