Posterior-stabilized (PS) total knee arthroplasty: a matched pair analysis of a classic and its evolutional design

Introduction: Total Knee Arthroplasty (TKA) designs continue to be modified to optimize patient’s outcome. This study showed that patient outcome was only partially influenced by design modifications applied to a classic posterior-stabilized (PS) TKA system. Methods: A consecutive group of 100 knees (group 1: 100 patients) undergoing TKA using a classic cemented fixed-bearing PS TKA system was matched by age, gender, BMI to 100 knees (group 2: 100 patients) having the newer cemented fixed-bearing PS design, both by the same manufacturer. Patients were assessed preoperatively, at 12 months and at 24 months minimum follow-up (range, 24-46) in a standard prospective fashion. The outcome assessments used were the Oxford Knee Score, the Knee Society Score (KSS), range-of-motion (ROM) and a satisfaction survey. A twosample t-test comparing the two groups was performed. Results: No patients were lost at follow-up. At 2-year follow-up, implant group 2 showed a statistically significant decrease in postoperative anterior knee pain (p=0.006), greater ROM (p=0.0009) and revision rate for any reason; differences in clinical and radiological KSS (p=0.09), Oxford Score (p=0.08) and overall satisfaction rate did not reach statistical significance. At follow-up, 16 % of group 1 knees achieved > 130° flexion compared with 37% in group 2. There were two revisions for any reason in group 1 and none in group 2. Conclusion: Design modifications applied to the newer TKA system allowed greater flexion and lower anterior-mechanism complications but not appeared to achieve better overall clinical scores.