LATERAL UNICOMPARTMENTAL KNEE REPLACEMENT: FIXED OR MOBILE BEARING?

Abstract

The aim of this prospective cohort study is to compare the early results in a single surgeon series of the mobile and fixed bearing versions of the Preservation UKR for lateral OA. Lateral UKRs were only considered for patients with isolated lateral compartment osteoarthritis with a functioning anterior cruciate ligament. Mild patellofemoral osteoarthritis was not considered a contraindication. If there was any doubt over the condition of the medial compartment or patellofemoral joint, single photon emission computed tomography was performed. Significant uptake it the medial or patellofemoral joint was considered a contraindication. Patients were assessed preoperatively and at 1 and 2 years postoperatively with the American Knee Society Score (AKSS), Oxford Knee Score (OKS) and with anteroposterior, lateral and Rosenberg radiographs.

Between 29^th May 2001 and 15^th May 2003, the senior author (GK) performed 233 consecutive Preservation UKRs. Of these, 30 were lateral UKRs (13%) performed in 12 men and 16 women (2 bilateral cases) with a mean age of 67 years (range 36 to 93 years). A metal-backed mobile bearing tibial component was used in 13 knees and an all-polyethylene fixed bearing tibial component in 17 knees. Patients in the mobile bearing group were significantly younger (t test; p< 0.0001) and had better AKSS knee (Mann-Whitney U test; p=0.05) and AKSS function scores (Mann-Whitney U test; p=0.005). The patients were reviewed after a minimum of 2 years (range 2 to 3.4 years). There was no significant difference between the 2 groups. There had been 3 revisions in the mobile bearing group for tibial loosening and none in the fixed bearing group (chi squared test; not significant). There was 1 tibial periprosthetic fracture in the fixed bearing group. This study shows that the choice of bearing type makes little difference in clinical outcome or range of motion over the first 2 years when using the Preservation Knee. A similar good functional result was obtained with a fixed bearing despite the mobile bearing group being younger and having significantly better preoperative AKS knee and function scores. The 3 revisions for tibial loosening in the mobile bearing group are a concern. However, these results are short-term and there may be improved implant longevity in the long-term with mobile bearing tibial components due to reduced polyethylene wear.