Fifteen-Year Results of Cementless Medial Oxford Unicompartmental Knee Arthroplasty

Background: The cementless Oxford Unicompartmental Knee Arthroplasty (OUKA) was introduced to minimize the risk of aseptic loosening, with evidence supporting its effectiveness for up to 10 years. However, it is not known if the fixation will be reliable thereafter and there is a concern that the interference fit of the cementless components may cause periprosthetic fractures. This prospective cohort study reports the 15-year survival and functional outcomes as well as the incidence of aseptic loosening and periprosthetic fracture. Methods: One thousand consecutive cementless OUKA, implanted between 2004 and 2017 for the recommended indications of antero-medial osteoarthritis (980) or avascular necrosis (20), were independently followed. Survival was assessed using various end points. The primary outcome measure was the Oxford Knee Score (OKS). Results: The mean OKS was 42 (SD 7.8) at 10 years and 41 (SD 8.8) at 15 years. 6% of knees were revised, and 1.2% had nonrevision reoperations. The 15-year survival for all reoperations was 89% (95% CI 86-92), for revision was 90% (CI 87-93), for conversion to TKA was 94% (CI 91-96.1), and for major revision needing revision TKA components was 99.4% (CI 98.8-100). The common causes for revision were lateral compartment arthritis (2.8%), pain (1.0%), bearing dislocation (0.9%), and fractured/worn bearing (0.6%). One aseptic femoral loosening occurred within the first year. There were no periprosthetic fractures. Conclusions: At 15 years, cementless OUKA, when used with the recommended indications and techniques, has excellent functional outcomes and good survival, with only 0.4% of knees needing revisions similar to those of TKA. Fixation was reliably achieved with only 1 case (0.1%) of loosening. This was an early failure of primary fixation of a femoral component due to damage to the fixation hole at surgery. There were no fractures related to the implants. Level of Evidence: The level of evidence is Level IV , therapeutic. See Instructions for Authors for a complete description of levels of evidence.