CHANGES IN VARUS-VALGUS LAXITY AFTER MOBILE-BEARING TOTAL KNEE ARTHROPLASTY WITH A MINIMUM FIVE-YEAR FOLLOW-UP

Abstract

Introduction: We performed a randomized, prospective, stress arthrometric study on 60 knees in 60 patients who had received mobile-bearing prostheses to determine the changes in varus–valgus laxity with time using a Telos arthrometer, and to evaluate the relationship between laxity and retention of the posterior cruciate ligament (PCL).

Materials and Methods: Thirty patients received PCL-retaining (PCLR) prostheses with an average of 75 months of follow-up (range: 60–106 months). Another 30 patients received PCL-sacrificing (PCLS) prostheses with an average of 78 months of follow-up (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 total knee arthroplasty (TKA) procedures were judged to be 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 six months, one year, two years, and five years after surgery. The intrasubject error was less than 1°.

Results: Varus laxity measurements with the PCLR prosthesis at six months, one year, two years, and five years were 3.7°, 4.0°, 4.1°, and 4.2°, respectively. With valgus laxity, measurements at the same time periods were 3.5°, 3.5°, 3.5°, and 3.6°, respectively. Varus laxity measurements with the PCLS prosthesis at six months, one year, two years, and five years were 4.3°, 4.3°, 4.3°, and 4.4°, respectively. With valgus laxity, measurements at the same time periods were 3.7°, 3.4°, 3.5°, and 3.6°, respectively. There were no significant differences in varus and valgus laxity between the PCLR and PCLS groups using repeated measure ANOVA methods (p > 0.05).

Discussion: Coronal laxity did not change with time in patients who had good clinical results. There were no significant differences between the PCLR and PCLS groups in changes in the varus-valgus laxity for a long time after the patients received prostheses. 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. Our results suggest that surgeons should appreciate the importance of obtaining balanced coronal laxity for long-term success following mobile-bearing TKA.