Risk factors associated with the occurrence of hip fracture in Japanese patients with rheumatoid arthritis: a prospective observational cohort study

Risk factors associated with the occurrence of hip fracture in Japanese patients with rheumatoid arthritis (RA) were evaluated in a prospective, observational cohort study. Physical disability, advanced age, history of total knee replacement (TKR), and low body mass index (BMI) appear to be associated with the occurrence of hip fracture. This study seeks to evaluate the association between potential risk factors and the occurrence of hip fractures in Japanese RA patients. A total of 9,720 patients (82.1 % female; mean age, 55.7 years) with RA were enrolled in a prospective observational study from 2000 to 2010. Self-reported hip fractures were verified using patient medical records. Cox proportional hazards models were used to analyze independent contributions of various risk factors to hip fracture occurrence. During a mean follow-up of 5.2 years, 152 patients reported 152 hip fractures. Among these patients, 97 hip fractures in 97 patients (15 males, 82 females) were verified with medical records. Japanese version of the Health Assessment Questionnaire (J-HAQ) disability score [per 1 score, hazard ratio (HR), 2.64; 95 % confidence interval (CI), 1.94-3.58], age (per 10 years; HR, 1.53; 95 % CI, 1.25-1.87), history of TKR (HR, 3.75; 95 % CI, 1.57-8.96), and BMI (per 1 kg/m(2), HR, 0.92; 95 % CI, 0.86-0.99) were significantly associated with hip fractures. Among the scores on the eight domains of the J-HAQ, J-HAQ (arising) (HR, 1.74; 95 % CI, 1.28-2.36) and J-HAQ (hygiene) (HR, 1.58; 95 % CI, 1.11-2.24) were significantly correlated with the occurrence of hip fracture. High J-HAQ disability score, advanced age, history of TKR, and low BMI appear to be associated with the occurrence of hip fractures in Japanese RA patients. Among the eight domains of the J-HAQ, arising and hygiene disabilities appear to be correlated with the occurrence of hip fractures in this patient population.