CLINICAL, FUNCTIONAL AND KINEMATIC RESULTS WITH AN ‘ACL-SUBSTITUTING’ KNEE ARTHROPLASTY DESIGN

Abstract

Outcomes following TKA often are good, but patients sometimes lack adequate range of motion and strength. Reasons for these deficits may include instability and the loss of cruciate ligament function. One approach to TKA design is to retain the PCL, and configure the TKA surfaces to approximate the function of the ACL. This can be accomplished by having a lateral surface that controls tibiofemoral motion near extension, but allows femoral rollback with flexion. We have been using such a fixed-bearing TKA design since 2001. The purpose of this study was to determine if an ‘ACL-substituting’ arthroplasty design provides clinical and functional results comparable to traditional PCL-retaining arthroplasty designs.

This series consists of 407 consecutive knees in 185 male and 222 female patients (73±9 years, 28±5 BMI) operated from November 2001 to August 2006. All patients underwent TKA by the same surgeon using PCL-retention and implantation of the same cemented ‘ACL-substituting’ TKA design. Clinical outcomes were evaluated using Knee Society Scores and radiographic review for the first 100 TKA with minimum 2 year follow-up. A subset of patients participated in IRB-approved protocols to quantitatively evaluate TKA motion and strength. Functional outcomes were assessed during gait, stair-climbing and curb step-over tasks for 10 unilateral TKA using a motion capture system, force platforms and inverse dynamics to measure the dynamic knee joint flexion moment. Kinematic outcomes were studied during kneeling for 20 TKA using fluoroscopy and shape matching techniques.

Knee Society Scores averaged 96+7 (pain) and 95+12 (function) at an average of 3.2+0.7 (range, 2 to 5) years follow-up. Passive flexion averaged 122°±10°, with 70% of the TKA achieving > 120° flexion. Radiolucent lines (2–4 mm wide) were observed in 7 TKA. Peak flexion moments (dynamic strength) for the TKA averaged 79%, 80% and 85% of the patients’ contralateral normal knees during the gait, stair-climbing and step-over tasks, respectively. In maximum kneeling, knees averaged 131°±13° flexion, 10° ±4° tibial rotation, and 2mm/10mm posterior position of the medial/lateral condyles.

This series’ early clinical follow-up was comparable to any well performing TKA. Knee flexion during passive examination and kneeling were comparable to the best reported results for PCL-retaining and PCL-substituting TKA. Peak knee flexion moments, a measure of functional strength, were comparable to the strongest knees reported in the literature. These early results suggest a fixed-bearing prosthesis with ‘ACL-substitution’ can provide patient performance comparable to the best performing designs.