DOES A NEW KNEE DESIGN PERFORM AS WELL AS THE DESIGN IT REPLACES?

Abstract

Introduction: When introducing new joint replacement designs, it is difficult to predict with any certainty the clinical performance of the new design. Using roentgen stereophotogrammetric analysis (RSA) to evaluate the first two years of follow-up may serve as a predictor of late mechanical loosening for both hip and knee prostheses. This randomized study was designed to evaluate the performance of the new Triathlon total knee system and compare the results to its predecessor design, the Duracon total knee system.

Methods: Sixty patients were consecutively randomized to receive either a Duracon (30 patients) or Triathlon total knee (30 patients). All components were cemented, and the posterior Cruciate Retaining version was used for both systems. The study was approved by the Ethical Committee for Lund University. All patients met the inclusion criteria. The mean age was 66 years (Duracon) vs 67 years (Triathlon). The BMI was 29 for both groups. The left knee was operated on in 15 vs 18 patients for the Duracon and for the Triathlon group. There were no statistically significant differences between the demographics for the two groups, except for the number of Ahlbäcks grade III OA, 20 (Duracon) vs 28 (Triathlon). The mean duration of surgery was 64 minutes (Duracon) vs 67 (Triathlon). The hospital stay was 5 days for both groups. The patients were followed up postoperatively at 3, 12 and 24 months. The principal evaluation tool was RSA to measure migration. The clinical results were evaluated using KOOS and KSS.

Results: There were no significant differences in rotation or translation for the three coordinal axes. Neither were there any significant differences in the Maximal Total Point Motion (MTPM) during the 2-year follow-up The MTPM for the Duracon and Triathlon groups respectively was 0.5±0.5 vs 0.4±0.3 mm at 3 months, 0.6±0.4 vs 0.6±0.5 mm at 1 year, and 0.8.±5 vs 0.6±0.7 mm at 2 years. There were no significant differences in the clinical results between the groups when using the KSS and the KOOS.

Discussion: The results of this study suggest that the new Triathlon total knee system is at least clinically equivalent to the Duracon total knee system. There were no significant differences in the RSA 2-year follow-up data nor in the clinical data (p< 0.05), which suggests the Triathlon knee system may replicate the excellent long-term clinical results achieved by the Duracon knee system.