Importance of joint line preservation in unicompartmental knee arthroplasty: Finite element analysis

Unicompartmental knee arthroplasty (UKA) is an effective surgical technique for pain relief and functional restoration in patients with localized osteoarthritis of the knee joint. However, the role of the joint line in UKA, especially its biomechanical effect, has not been previously investigated. This study numerically evaluates the effects of the joint line on the contact stresses in polyethylene (PE) inserts, articular cartilage, and lateral meniscus using the finite element (FE) analysis. The FE model for joint line was modeled as the orthogonal projection line from the medial tibial plateau to the anatomical axis. The joint line was varied from -6 to +6 mm in 2 mm intervals, and the seven FE models were analyzed and compared under ISO gait loading conditions. The contact stresses in the PE insert, articular cartilage, and lateral meniscus matched those of the reference joint line (0 mm) in the ±2 and ±4 mm joint line cases but significantly differed from the reference in the ±6 mm joint line cases. On the +6 mm joint line, the contact stress was greater on the PE insert than on the articular cartilage, whereas the reverse occurred on the -6 mm joint line. This study confirms the post-operative significance of joint line preservation in UKA implantation surgery. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:347-352, 2017.