The modification of bone cut angle and joint line obliquity did not change the tibiofemoral kinematics and stability of knee joint after total knee arthroplasty.

INTRODUCTION: Previous reports using cadaveric knees and musculoskeletal computer simulation have shown that kinematically aligned (KA) total knee arthroplasty (TKA) provides more natural and physiological tibiofemoral kinematic patterns than mechanically aligned (MA) TKA. These reports suggested that the modification of joint line obliquity improve the knee kinematics. This study aimed to determine whether joint line obliquity change the intraoperative tibiofemoral kinematics in TKA candidates with knee osteoarthritis.

METHODS: Thirty consecutive knees with varus osteoarthritis that underwent TKA using a navigation system were evaluated. Two types of trial components were prepared: (1) MA TKA model: component trial in which articulating surface was parallel to the bone cut surface (2) KA TKA model: the femoral component trial, which mimicked the KA TKA method of Dossett et al. was designed 3° valgus and 3° internal rotation to the femoral bone cut surface, and the tibial component trial was designed 3° varus to the tibial bone cut surface. These two trials were set on the same knees during the operation, and the tibiofemoral rotational kinematics and varus-valgus laxity were measured from 0° to 120° of knee flexion using a navigation system.

RESULTS: The joint gap was 20 ± 2 mm and 3° ± 1° varus in extension and 20 ± 2 mm and 3° ± 1°varus in flexion. The differences in femoral component rotation between KA TKA and MA TKA were not statistically significant for any knee flexion angle. The differences in varus-valgus laxity between KA TKA and MA TKA were also not statistically significant for any knee flexion angle.

CONCLUSION: Although the degree of joint line obliquity varies widely in various KA TKA methods, this study, which mimicked the method of Dossett et al. showed that the modification of joint line obliquity did not change the tibiofemoral kinematics and stability of the knee joint in TKA candidates with knee osteoarthritis.