抄録
Objective: It is known that high flexion in the normal knee is associated with internal rotation of tibia, but whether this rotation is reproduced in total knee arthroplasty (TKA) remains uncertain. It is assumed that different axial rotation magnitudes and patterns may occur after TKA. The purpose of this study was to intraoperatively evaluate the magnitudes and direction of axial tibiofemoral rotation in deep knee flexion.
Methods: One hundred and thirty-eight consecutive patients who underwent 156 primary mobile-bearing, posterior-stabilized TKAs were included. All the operations were performed by senior author (Y.K.) or under his supervision, using the gap balancing technique. After all the bone cut and soft tissue releases were completed, the flexion angle and tibiofemoral rotation were measured with specially designed trial components with the mobile-bearing mechanism in flexion under gravity and in manual passive maximum flexion. For the measurement of the flexion angle, the knees were photographed and the picture data was transferred to a personal computer. Because of the high conformity of the femoral component and tibial insert, no rotation could occur between the femoral component and the polyethylene insert.
Results: The mean flexion angle was 124.1°±9.5° (range, 99°-144°) under gravity and 136.7°±9.6° (range, 108°-156°) in passive maximum flexion. During this flexion arc (12.9°±3.5° range, 4°-23°), the average amount of the rotation was small measuring 1.3°±3.6° of internal rotation (range, external 12°-internal 12°). One hundred and eleven knees (71.2%) showed less than 3° of rotation and in 51 knees (32.7%) showed no rotation.
Conclusion: It has been reported that deep knee flexion in normal knees is always associated with significant internal rotation of the tibia. Intraoperative measurements in the current study have shown however, that the direction of tibial rotation in passive maximum flexion is unpredictable. In addition, the overall amount is negligible (approximately 1.3°) and absent in 32.7% of the knees. This information should be considered in the design of knee prostheses which aims to achieve deep knee flexion. The possible advantage for mobile-bearing TKA would be the ability to accommodate a wide and unpredictable range of axial rotation in deep flexion.
