Polyethylene bearing wear is comparable for cemented and cementless Oxford unicompartmental knee replacements: Ten-year results of a randomized controlled trial.

PURPOSE: There is concern that using cementless components may increase polyethylene wear of the Oxford unicompartmental knee replacement (OUKR). Therefore, this study aimed to measure bearing wear at 10 years in patients from a randomized trial comparing Phase 3 cemented and cementless OUKRs and to investigate factors that may affect wear. It was hypothesized that there would be no difference in wear rate between cemented and cementless OUKRs. METHODS: Bearing thickness was determined using radiostereometric analysis at postoperative, 3-month, 6-month, 1-year, 2-year, 5-year and 10-year timepoints. As creep occurs early, wear rate was calculated using linear regression between 6 months and 10 years for 39 knees (20 cemented, 19 cementless). Associations between wear and implant, surgical and patient factors were analysed. RESULTS: The linear wear rate of the Phase 3 OUKR was 0.06 mm/year with no significant difference (p = 0.18) between cemented (0.054 mm/year) and cementless (0.063 mm/year) implants. Age, Oxford Knee Score, component size and bearing thickness had no correlation with wear. A body mass index ≥ 30 was associated with a significantly lower wear rate (p = 0.007) as was having ≥80% femoral component contact area on the bearing (p = 0.003). Bearings positioned ≥1.5 mm from the tibial wall had a significantly higher wear rate (p = 0.002). CONCLUSIONS: At 10 years, the Phase 3 OUKR linear wear rate is low and not associated with the fixation method. To minimize the risk of wear-related bearing fracture in the very long-term surgeons should consider using 4 mm bearings in very young active patients and ensure that components are appropriately positioned, which is facilitated by the current instrumentation. LEVEL OF EVIDENCE: Level III, retrospective comparative study.

Fixed lateral unicompartmental knee replacement is a reliable treatment for lateral compartment osteoarthritis after mobile-bearing medial unicompartmental replacement.

PURPOSE: Lateral osteoarthritis following medial unicompartmental knee replacement (UKR) is usually treated with total knee replacement, however, lateral UKR is a less invasive option that preserves a well-functioning medial UKR. This study aimed to determine the 5-year outcome of the cemented Fixed Lateral Oxford UKR (FLO) when used for the treatment of severe lateral disease after medial Oxford unicompartmental knee replacement. METHODS: Forty-four knees with lateral bone-on-bone osteoarthritis (n = 43) and avascular necrosis (n = 1) treated with the FLO following medial Oxford UKR were followed up prospectively. The Oxford Knee Score (OKS) and Tegner Activity Score (TAS) were collected pre- and post-operatively. Life-table analysis was used to determine survival rates. RESULTS: The mean patient age at the time of FLO surgery was 74.4 years with a mean time of 12.1 years between the primary medial UKR and the conversion to a bi-UKR with a FLO. Mean follow-up of the FLO was 3.5 years. After FLO no intra-operative or medical complications, re-admissions, or mortality occurred. There was one reoperation in which a bearing was exchanged for a medial bearing dislocation. There were no revisions of the FLO, so the FLO survival rate at 5 years was 100% (24 at risk). The mean pre-operative OKS was 22, which significantly (p < 0.0001) improved to a mean of 42, 42, and 40 at 1, 2, and 5 years, respectively. The median TAS had a non-significant improvement from 2.5 (Range 0-8) pre-operatively to 2 (Range 1-6) at 5 years postoperatively. CONCLUSION: The FLO is a reliable treatment for lateral osteoarthritis following medial UKR. At 5 years there was a 100% survival of the FLO with a mean OKS of 40. LEVEL OF EVIDENCE: IV, Prospective Case Series.