Osteonecrosis of the hip in Korean patients with systemic lupus erythematosus: risk factors and clinical outcome

Objective The objective of this paper is to identify the risk factors for development of symptomatic osteonecrosis (ON) and predictors of total hip replacement (THR) among systemic lupus erythematosus (SLE) patients in Korea. Methods The medical records of 1051 patients with SLE were reviewed, and 73 patients with symptomatic ON were identified. Among them, 64 patients were eligible for the analysis. Sixty-four age- and sex-matched SLE patients without apparent ON were included as disease controls. The risk factors for development of symptomatic ON were identified by logistic regression analyses. The predictors of THR were determined by Cox proportional hazards regression analyses. Results Among 64 patients with ON, 59 had ON of the hip and 36 underwent THR. Independent risk factors for development of symptomatic ON included Cushingoid body habitus (OR 21.792 (95% confidence interval (CI) 2.594-183.083)), use of cyclophosphamide (OR 2.779 (95% CI 1.106-6.981)) and azathioprine (OR 2.662 (95% CI 1.143-6.200)). In the Cox proportional hazards model, only advanced radiological stage of ON (Association for Research on Osseous Circulation (ARCO) stage) was a statistically significant predictor of THR. In subgroup analysis with stage I-III ON, multivariate Cox regression analysis showed neuropsychiatric SLE (NPSLE) (HR 6.295 (95% CI 2.178-18.192)) and cumulative prednisolone dose in the first six months after ON diagnosis>0.9g (HR 3.238 (95% CI 1.095-9.58)) to be independent predictors. Conclusions Advanced ARCO stage at the onset of ON is an independent risk factor for THR in SLE patients with ON. In ARCO stage I-III ON, patients with NPSLE and those receiving>0.9g prednisolone during the first six months after the ON diagnosis are likely to require THR.