DOES THE MEDIAL PIVOT DESIGN WORK? A COMPARATIVE ANALYSIS OF MEDIAL PIVOT AND POSTERIOR STABILISED KNEE ARTHROPLASTY

Abstract

Background: Knee prosthesis design is being constantly altered in a bid to imitate kinematics of the normal knee. It is hoped that this will improve the wear characteristics and performance of the implant. The ‘Medial Pivot’ knee has a characteristic geometry and is expected to lower contact stresses on the tibial surface and ease rehabilitation while providing greater stability.

We conducted a study comparing the midterm outcome of the Medial Pivot knee (MP) to the Posterior Stabilised (PS) knee.

Materials and Methods: Over a 3 year period, 312 knee replacements were carried out of which 124 were MP and 188 were PS. 100 patients from each of the 2 groups were called for review. Demographic data, age at operation, time since surgery and ASA grading were noted. Postoperative knee function was assessed using the American Knee Society (AKS) and Oxford Knee (OK) scores and the scores were compared between the 2 groups. Individual functional parameters were also compared.

Results: 38 patients with 42 replaced knees in the MP group and 43 patients with 52 replaced knees in the PS group were reviewed. The 2 groups were comparable in terms of gender of patients and age at operation and were followed up to a mean 31 months. For the MP group the mean AKS knee assessment score was 77/100, AKS function score was 75/100 and OK Score was 23/60. For the PS group the corresponding values were 81/100, 77/100 and 22/60. The differences in scores between the groups were not statistically significant. Only active and passive knee extension was better following MP Arthroplasty than PS arthroplasty (p< 0.05). Although the mean flexion was better following the PS arthroplasty, this was not statistically significant.

Conclusion: Our study has shown that the midterm outcome for the Medial Pivot knee system did not show any distinct advantage over the Posterior Stabilised knee system in terms of knee pain & function.