To investigate the association between extent of subchondral bone marrow edema (BME) as classified by magnetic resonance imaging (MRI) and intermediate to long-term outcomes after unicompartmental knee arthroplasty (UKA) for medial compartment osteoarthritis.
We enrolled 150 knees (144 patients) that underwent fixed-bearing UKA between April 2003 and December 2014 with a minimum follow-up of 5 years; the mean overall follow-up duration was 9.8 years (5.1 to 17.7 years). We divided the patients into two groups based on the presence or absence of preoperative BME. Patients were also subdivided into four groups according to their BME scores determined by the MRI Osteoarthritis Knee Score (MOAKS) method. Clinical outcomes were assessed using the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) and Forgotten Joint Score. Furthermore, survival rates and relevant risk factors that affect joint survivorship were analyzed.
The groups with BME demonstrated significantly worse postoperative WOMAC pain and Forgotten Joint Scores at the final follow-up than the group without BME. (all p < 0.05). We also found significant differences among the scores of groups with different BME grades (all p < 0.05). Post hoc analysis demonstrated differences between groups 1 and 2, 1 and 3, 1 and 4, and 2 and 4 (all p < 0.05) with a significant correlation between postoperative clinical outcome and the extent of BME (r = 0.430 [WOMAC pain], r = -0.342 [Forgotten Joint Score]; p < 0.05). The survival rate was 95.4% at a mean period of 9.8 years, and survival was not associated with the presence of BME (p = 0.232; log-rank test).
In the intermediate to long-term follow up, preoperative BME negatively impacted the clinical outcomes after UKA, although UKA contributed to excellent survival rates after a mean follow-up of 9.8 years regardless of BME severity.