Spontaneous Osteonecrosis of the Knee Is Associated With Increased Five-Year Implant Complications Compared to Osteoarthritis Patients Undergoing Primary Total Knee Arthroplasty.

Abstract

Spontaneous osteonecrosis of the knee (SPONK) is a potential, although uncommon, indication for total knee arthroplasty (TKA). Unlike secondary osteonecrosis, SPONK typically affects a single femoral condyle in patients over 50 years of age and is sometimes treated with TKA once joint-preserving strategies fail. However, implant survivorship of TKA for SPONK versus osteoarthritis (OA) remains under-characterized. This study aimed to compare outcomes, including (a) mechanical complications (aseptic loosening, periprosthetic fracture), (b) periprosthetic joint infection, and (c) all-cause revision, between patients undergoing TKA for SPONK and OA at two and five years. We retrospectively queried a nationwide database to identify 43,680 patients who underwent TKA from 2010 to 2021, including 7,282 patients who had SPONK matched by age, sex, and comorbidities to 36,398 patients who had OA. Implant-related complications were assessed at two and five years. Multivariable logistic regressions computed the odds ratios (ORs) and 95% confidence intervals with a significance threshold of P < 0.001. Among mechanical complications, patients undergoing TKA for SPONK had a significantly higher risk of aseptic loosening at both two (OR: 1.52, P < 0.001) and five years (OR: 1.63, P < 0.001) compared to OA. Similarly, elevated risk of periprosthetic fracture was observed at five years (OR: 2.15, P < 0.001). The 5-year risk of periprosthetic joint infection was higher for SPONK patients (OR: 1.33, P < 0.001), as was the two- (OR: 1.37, P < 0.001) and 5-year (OR: 1.48, P < 0.001) risk of all-cause revision. Patients over the age of 50 years undergoing TKA for SPONK have a significantly increased risk of implant-related complications compared to those who had OA, particularly for aseptic loosening, periprosthetic fracture, periprosthetic joint infection, and all-cause revision. These findings suggest that TKA may not represent the optimal first-line arthroplasty for isolated SPONK and likely should be reserved for more advanced or multicompartmental disease or salvage procedures following treatment failure.