Mobile bearing shows larger rollback motion than fixed bearing in total knee arthroplasty using a medial stabilising technique with a navigation system.

Purpose: This study aimed to investigate the intraoperative knee kinematics of cruciate-retaining total knee arthroplasty with a medial stabilising technique (MST-TKA) and compare the kinematics between mobile- and fixed-bearing MST-TKAs. We hypothesised that mobile-bearing MST-TKA would result in greater physiological kinematic motion than fixed-bearing MST-TKA.

Methods: Twenty-one and 20 knees underwent mobile- and fixed-bearing MST-TKAs using a navigation system (Orthopilot® ver. 6.0; B. Braun Aesculap), respectively. In the preoperative and postoperative kinematic analysis, the knee was moved manually from 0° to 120°, and femoral anteroposterior translations of the medial femoral condyle (MFC) and lateral femoral condyle (LFC) were recorded every 0.1 s from 0° to 120°. Data were subsequently extracted from the software every 10° of flexion and compared between the two groups, and the correlation coefficients between preoperative and postoperative kinematics were calculated.

Results: In the postoperative analysis, the MFC in the mobile-bearing group showed significant posterior translation at 100°, 110° and 120° compared to the fixed-bearing group ( < 0.01). Similarly, the LFC in the mobile-bearing group showed significant posterior translation at 100°, 110° and 120° compared to the fixed-bearing group ( < 0.05,  < 0.01 and  < 0.05, respectively). In the mobile-bearing group, the preoperative and postoperative anteroposterior translations of the MFC and LFC were correlated ( < 0.01), while in the fixed-bearing group, there was no correlation.

Conclusion: The femoral rollback motion in the mobile-bearing MST-TKA correlated with the preoperative kinematics and was larger than that in the fixed-bearing group.

Level Of Evidence: Level II, therapeutic prospective cohort study.