Antiphospholipid score is a novel risk factor for idiopathic osteonecrosis of the femoral head in patients with systemic lupus erythematosus

Abstract Objective Idiopathic osteonecrosis of the femoral head (ION) is a common complication of SLE associated with CS therapy. Although the pathogenesis of ION involves local bone ischaemia favoured by thrombophilia, the involvement of aPL in lupus ION remains to be elucidated. We have previously reported the aPL score (aPL-S) as a quantitative marker of aPL and the development of thrombotic events in autoimmune diseases. The aim of this study was to identify the impact of aPL on the development of ION using aPL-S. Methods This was a single-centre retrospective study comprising 88 consecutive SLE patients who underwent MRI of the hip joints from January 2000 to March 2017. Baseline characteristics, pharmacotherapy and total hip arthroplasty performed during follow-up were evaluated. Results The presence of ION was confirmed by MRI scan in 38 patients (43.1%). Male gender, positivity of any aPL, aPL-S, high aPL-S (≥30) and high dose of CS were identified as risk factors for ION by univariate analysis. Multivariate analysis revealed high aPL-S (odds ratio 5.12, 95% CI 1.18–29.79) and use of high-dose CS (odds ratio 10.25, 95% CI 3.00–48.38) as independent variables. Kaplan–Meier analysis showed that patients with high aPL-S received total hip arthroplasty more frequently than those without aPL (P = 0.010). Conclusions We newly identified high aPL-S as an important risk factor for ION development in SLE, suggesting the involvement of aPL-induced coagulopathy in the pathophysiology of lupus ION.