Symptomatic knee osteonecrosis in patients with systemic lupus erythematosus: a case-control study

To explore the associated risk factors of symptomatic knee osteonecrosis (KON) in patients with systemic lupus erythematosus (SLE), we conducted a retrospective case-control study to compare the clinical and laboratory features between SLE patients with and without symptomatic KON matched by age and gender. Univariate and multivariate regression analyses were used to evaluate possible associated risk factors. Twenty (one male, nineteen females) out of 3941 lupus patients were identified as symptomatic KON, which was confirmed by magnetic resonance imaging. The mean age at KON onset was 34.4 (range 12-67) years, and the median course of lupus at KON onset was 72.5 (range 8-123) months. Univariate and multivariate analyses identified that the prevalence of cutaneous vasculitis (OR 5.23; 95 % CI 1.11-24.70), hyperfibrinogenemia (OR 4.75; 95 % CI 1.08-20.85), and elevated IgG levels (OR 6.05; 95 % CI 1.58-23.16) were statistically higher in KON group, and hydroxychloroquine (HCQ) usage was statistically lower in KON group (OR 0.27; 95 % CI 0.07-0.97). Glucocorticoid usage, in terms of maximal dose, duration of treatment, and the percentage of receiving methylprednisolone pulse therapy, did not show statistical difference between the two groups (p > 0.05). Symptomatic KON is a relatively rare complication of SLE. Cutaneous vasculitis, hyperfibrinogenemia, and elevated IgG levels are possible risk factors, whereas HCQ may provide a protective effect. Our results suggest that lupus activity as well as hypercoagulation status may play a role in the pathogenesis of KON in lupus.