In Vivo Laxity of Low Contact Stress Mobile-Bearing Prostheses

A stress arthrometric study was done on 60 knees in 54 patients with total knee arthroplasties using a Telos arthrometer, to determine anteroposterior and abduction and adduction laxity and to evaluate the relationship between laxity and retention of the posterior cruciate ligament using low contact stress mobile-bearing prostheses. Thirty knees had posterior cruciate ligament-retaining and 30 had posterior cruciate ligament-sacrificing prostheses. The selected patients had successful knee arthroplasty 6 months previously. Anteroposterior displacement was measured at 30° and 90° flexion; there were no statistically significant differences between the posterior cruciate ligament-retaining (10.5 mm at 30°, 9.3 mm at 90°) and posterior cuciate ligament-sacrificing (9.8 mm at 30°, 9.7 mm at 90°) groups. Abduction and adduction were between 0° and 20° flexion, there were no significant differences between the two groups. Because all the patients in this study had good clinical results, approximately 10 mm anteroposterior displacement and 4° laxity in the coronal direction are considered favorable in low contact stress mobile-bearing prostheses of both designs.