PATIENTS WITH ROTATIONAL MISMATCH BETWEEN FEMUR AND TIBIA AFTER TKA SHOW NO IMPROVEMENT IN THE KNEE SOCIETY FUNCTION SCORE AND DIFFERENT KINEMATICS

Abstract

Background: As many as 20% of all patients after total knee arthroplasty (TKA) are not satisfied with their result. Different factors affecting clinical outcome include leg alignment, rotational alignment, soft tisssue-balancing, the femoro-patellar joint, and patient-related factors. The purpose of this study was to assess relationships between prosthesis rotational alignment, function score and knee kinematics after TKA.

Materials and Methods: From initially eighty patients with a cemented, unconstrained, cruciate-retaining TKA with a rotationg platform without patellar resurfacing seventy-three patients were available for post-operative physical and radiological examination after a median of 20 months follow-up.

Results: Nine patients had more than 10° rotational mismatch between the femoral and tibial component in the postoperative CT-scans. These patients were not different from the remaining 64 patients in the KSS Knee score (both groups 89 points at follow-up) and EQ 5D VAS (65 points vs 70 points at follow-up) but showed significantly worse results in the KSS Function score. While the normal patients with less than 10° rotational mismatch impoved from a median preoperative 55 points to a median 70 points at follow-up, the group with more than 10° mismatch deteriorated from a median 60 points preoperatively to a median 50 points at follow-up (p = 0.001).

For seven of these nine patients, kinematic analysis was available during passive flexion from approximately 0° to 120°. There were no substantial differences in the average range of total axial rotation achieved in this group compared to the normal group, but the pattern of motion during that range was quite different. While external rotation steadily increased with knee flexion in the normal group, there was internal rotation between 30° and 80° of flexion in the group with more than 10° rotational mismatch.

Conclusion: Rotational mismatch between femoral and tibial components exceeding 10° resulted in different kinemtics after TKA. This might contribute to worse clinical results observed in those patients and should therefore be avoided.