Summary

In this study, mobile bearing CR TKA showed significantly greater posterior translation of the lateral femoral condyle in the 90° to 120° flexion position.

Abstract

Purpose

In recent years, there have been many reports on intraoperative kinematics in total knee arthroplasty (TKA) using navigation systems, in addition to those examining clinical outcomes and alignment. This study aimed to compare the intraoperative kinematics of mobile bearing and fixed bearing TKA using intraoperative navigation data.

Methods

Forty patients (8 males and 32 females) underwent TKA. Implants were used in 20 patients with e-motion CR (Aesculap) in the mobile bearing group and Columbus CR (Aesculap) in the fixed bearing group. Surgery was performed using the OrthoPilot Navigation System (Aesculap) with a medial stabilizing technique. The amount of posterior translation (mm) of the lateral femoral condyle and medial femoral condyle to the tibia was calculated from the intraoperative data from 0° to 120° by 15°. The amount of posterior translation of the lateral femoral condyle and medial femoral condyle at each flexion angle between the two groups was compared.

Results

The posterior displacement of the femoral epicondyle at 15° and 30° was 0.06 mm and 0.8 mm in the mobile bearing group and 1.5 mm and 1.1 mm in the fixed bearing group. On the other hand, the posterior displacement of the external femoral condyle at 90°, 105°, and 120° was 2.6 mm, 5.5 mm, and 6.2 mm in the mobile bearing group and 0.2 mm, 0.7 mm, and 1.5 mm in the fixed bearing group, respectively, with the mobile bearing group showing significantly greater posterior displacement. There was no significant difference in the amount of posterior translation of the external femoral condyles at 45°, 60°, and 75°.
The amount of posterior translation of the endocondyle of the femur at 15°, 30°, and 45° was 0.03 mm, 0.1 mm, and 0.1 mm in the mobile bearing group and 1.7 mm, 2.6 mm, and 2.7 mm in the fixed bearing group, respectively, showing significantly smaller posterior translation in the mobile bearing group. There was no significant difference in the amount of posterior shift of the medial femoral condyle from 60° to 120°.

Discussion

In this study, mobile bearing CR TKA showed significantly greater posterior translation of the lateral femoral condyle in the 90° to 120° flexion position. In a normal knee, the medial femoral condyle hardly moves back and forth until 120° of flexion, while the lateral femoral condyle moves backward in medial pivot motion. Mobile bearing TKA may show intraoperative kinematics closer to those of the normal knee than fixed bearing CR TKA.