Hip fractures have serious consequences, including a 1-year mortality rate of 30%. Population-based studies on hip fractures in individuals with systemic lupus erythematosus (SLE) are scarce. Our objective was to assess the independent risk of hip fractures in patients with newly diagnosed SLE compared to the general population, accounting for baseline and time-varying confounders.
A cohort of all patients with incident SLE who received health care between January 1, 1997 and March 31, 2015 was assembled. The primary outcome was the occurrence of the first hip fracture since the study entry date. Individuals without SLE were randomly selected from the general population and matched (5:1) to those with SLE based on age, sex, and index year. Cumulative incidence was calculated after accounting for competing risks of death. Marginal structural Cox models were used to estimate the impact of SLE on hip fractures, adjusting for baseline and time-dependent covariates (i.e., glucocorticoid use and the number of outpatient, inpatient, and rheumatologist visits).
Among 5,047 individuals with incident SLE and 25,235 individuals without SLE (86% female, mean age 40 years), we found 73 and 272 hip fractures during 78,915 and 395,427 person-years, respectively. The crude incidence rate ratio was 1.34 (95% confidence interval [95% CI] 1.02-1.75). After adjusting for baseline covariates, the hazard ratio (HR) was 1.86 (95% CI 1.37-2.52). After further adjustment for time-dependent covariates, the HR remained significant at 1.62 (95% CI 1.06-2.48).
Patients with newly diagnosed SLE have a 62% increased risk of hip fractures compared to individuals without SLE. For patients with SLE, this result has important implications for prevention of osteoporosis, which may lead to hip fractures.