Unicompartmental knee arthroplasty for spontaneous osteonecrosis of the knee: A meta-analysis

Background: Spontaneous osteonecrosis of the knee (SONK) is a poorly understood but debilitating disease entity. Total knee arthroplasty (TKA) is the standard of care for those patients who fail conservative management, but considering SONK's predilection for affecting a single knee compartment, unicompartmental knee arthroplasty (UKA) appears to be a more tailored option. Unfortunately, conflicting data exist on the utility of UKA in SONK. Thus, the purpose of this study was to evaluate functional outcomes and revision rates of UKA in the setting of SONK. Methods: A systematic literature search was performed to evaluate all studies examining patients who underwent UKA for SONK. Screening of the articles was performed using multiple Boolean search strings, methodological index for non-randomized studies criteria, and other selected exclusion criteria. Results: Seven studies were included, with a total of 276 knees (273 patients). The mean age was 68 years (64-74 years), with a mean body mass index of 26 kg/m(2) (25-29 kg/m(2)). The final range of motion was 125 degrees (124-126 degrees). Standardized mean difference (SMD) of clinical improvement pre- and post-outcome was 3.39 (p < 0.001). The improvement in the visual analog score was 57.03 points, with an SMD of 4.57 (p < 0.001). Revision rates were determined to be 5.51% (95% confidence interval of 1.96-10.69%). Conclusion: Our meta-analysis demonstrated that in properly selected patients, UKA could be an excellent alternative to TKA for patients with SONK. These data show that UKA has few complications, significant improvements on functional outcomes, and good survivorship at a mean follow-up of 6 years.