Symptomatic osteonecrosis of the hip and knee in patients with systemic lupus erythematosus: Prevalence, pattern, and comparison of natural course

Objective Osteonecrosis (ON), also known as avascular necrosis, is characterized by the collapse of the architectural bone structure secondary to the death of the bone marrow and trabecular bone. Osteonecrosis may accompany many conditions, especially rheumatic diseases. Among rheumatic diseases, osteonecrosis is most commonly associated with systemic lupus erythematosus (SLE). We assessed prevalence and distribution pattern of symptomatic ON in patients with SLE and compare the natural courses of hip and knee ON. Methods 912 SLE patients admitted between 1981 and 2012 were reviewed. SLE patients with symptomatic ON were retrospectively identified both from the existing SLE/APS database. The prevalence of symptomatic ON was calculated; with ON, the joint involvement pattern was determined by examining the distribution of the joints involved, and then the data about the hip and knee joints were entered in the Kaplan-Meier analysis. Kaplan-Meier methods were used to calculate 5- and 10-year rates of ON-related hip (the hip group) and knee survival (the knee group). Results Symptomatic ON developed in various joints in 97 of 912 patients with SLE, and the overall prevalence of ON was detected as 10.6%. The mean age at the time of SLE and ON diagnoses were 27.9 +/- 9.9 (14-53) and 34.2 +/- 11.3 (16-62) years, respectively. The mean duration from diagnosis of SLE to the first development of ON was 70.7 +/- 60.2 (range = 0-216) months. The most common site for symptomatic ON was the hips (68%, n=66), followed by the knees (38%, n = 37). According to Kaplan-Meier analysis, hip and knee joint survival rates associated with 5-year ON were 51% and 88%, and 10-year survival rates were 43% and 84%, respectively. Conclusion We observed that the prevalence of symptomatic ON in patients with SLE was 10.6%. With the estimated 10-year survival rates of 40% versus 84% for the hip and knee joints, respectively, hip involvement may demonstrate a more aggressive course to end-stage osteoarthritis than the knee involvement