A randomized, prospective stress arthrometric study was done on 60 knees in 60 patients, using a Telos arthrometer to determine the changes of varus-valgus laxity with time and to evaluate the relationship between laxity and retention of posterior cruciate ligament (PCL) using mobile bearing prostheses.

Thirty knees had PCL -retaining (PCLR) with an average 75 months follow-up (range; 60–106 months) and 30 had PCL-sacrificing (PCLS) prostheses with an average 78 months (range; 60–109 months). In all patients, the preoperative diagnosis was osteoarthritis. The coronal conformity of the PCLR and PCLS designs was similar. All of the TKA procedures were judged clinically successful (Hospital for Special Surgery scores: PCLR 92 ±4 points, PCLS 92 ±3 points). The patients had no clinical complications. Varus-valgus laxity was measured with the knee in extension at 6 months, 1 year, 2 year and 5 year after surgery. The intrasubject error was less than 1 degree.

Laxity with PCLR at 6 months, 1, 2 and 5 years was 3.7, 4.0, 4.1, 4.2 degrees with varus, 3.5, 3.5, 3.5, 3.6 degrees with valgus laxity. Laxity with PCLS was 4.3, 4.3, 4.3, 4.4 degrees with varus, 3.7, 3.4, 3.5, 3.6 degrees with valgus laxity. The changes of the varus and valgus laxity had no significant differences in both PCLR and PCLS groups using a repeated measure ANOVA methods (p> 0.05).

The coronal laxity has proved to be no changes with time for the patients who have clinical good results. The changes of the varus-valgus laxity for long timehad no significant differences in both PCLR and PCLS groups. Therefore, we conclude that the PCL doesn’t affect coronal stability in Extension and that the characteristics of the component geometry may act as a resistance factor. We surgeons should have a new understanding of the importance to obtain the balanced coronal laxity for successful mobile-bearing TKA for long period.