Comparison of Kinematics and Clinical Outcomes of Two Designs of Mobile Bearing Total Knee Arthroplasty : Ultracongruent vervus Posterior Stabilized

Abstract

ABSTRACT

Introduction: There is no consensus as to whether to use posterior cruciate ligament sacrificing ultracongruent (UC)mobile TKA and posterior cruciate ligament substituting posterior stabilized(PS) mobile TKA. The purpose of this study is to assess kinematics and clinical outcomes of ultracongruent (UC) and posterior stabilized (PS) rotating-platform mobile bearing TKA. Methods: Ninety primary osteoarthritis knees were randomized to undergo computer assisted TKA with UC (n=45) or PS (n=45) prostheses and eighty two knees (UC: 42 knees, PS: 40 knees) were followed up for a minimum 3-years. The passive kinematic evaluation was performed before and after the implantation with a navigation system. Three parameters of tibiofemoral relationship (anterior/posterior translation, varus/valgus alignment and rotation) were recorded from 0° to 120° of flexion. The patients were clinically and radiographically evaluated at the 3-year follow-up. Results: Paradoxical anterior translation of the femur was observed from 0° to 82° of flexion in the UC knees (10.8mm) and 0° to 70° in the PS knees(8.7mm). The lengths of femoral roll-back in the UC knees and PS knees was 5.6mm and 6.7mm respectively, but never reached the starting point. Paradoxical internal rotation of the femur was found from 0° to 47° of flexion in the UC knees (5.8°) and 0° to 62° in the PS knees (9.9°). The femur of UC group was more externally rotated from 40º to 120º compared to the PS group. But, in regard to the coronal alignment, there was no significant difference between the groups. There was no significant difference in the maximal flexion(123°:125°, p=0.411), KS knee scores(91:94, p=0.221), KS function scores(81:84, p=0.588) and WOMAC index scores(15:15, p=0.540). There was no progressive radiolucent line or loosening in all knees. Conclusions: With knee flexion, mobile UC TKA showed more anterior translation and external rotation of the femur when compared to the mobile PS TKA. Although the kinematic result of UC mobile TKA was different from that of PS mobile TKA, the range of knee motion and other clinical outcomes were similar to PS knees