Background Hip fractures (HP) have serious long-term effects, including 1 year mortality rate of up to 30% and poor functional recovery. Studies on the risk of HP fracture in SLE are limited due to the use of selected samples, failure to adjust for time-varying treatments and confounders. Our objective was to assess the risk of HP in patients with newly diagnosed SLE compared to the general population.
Methods Using physician billing data and a previously validated SLE case definition, we assembled an incident cohort of all patients with SLE who received care between January 1997 and March 2015 in the province of British Columbia, Canada. The main outcome was the first ever HP during follow-up. HP (ICD-9-CM codes 820.0, 820.2; ICD-10-CM codes S72.0, S72.1, S72.2) were identified using hospitalization data. We excluded patients with previous HP, pathological fractures or Pagets disease before the index date (SLE diagnosis). Non-SLE controls were randomly selected from the general population and matched (1:5) to SLE patients on birth year, sex, and index year. First, we used Kaplan-Meier estimates and log-rank test to compare time to first hip fracture between SLE and non-SLE controls. Multivariable analyses adjusting for baseline covariates known as potential risk factors for HP were done. In addition, marginal structure Cox models were then used to estimate the impact of having SLE on the risk of hip fracture, adjusting for time-dependent covariates, including glucocorticoid use, number of outpatient, inpatient and rheumatologist visits.
Results We identified 5047 patients with a new diagnosis of SLE and 25 235 non-SLE controls (mean age 40 years; 86% females for each cohort), yielding 73 and 273 HP, respectively. The incidence rate for HP for SLE and non-SLE were 0.93 and 0.69 per 1000 person-years, respectively. Patients with SLE had a higher risk of HP (p<0.001, figure 1). The age- and sex-adjusted hazard ratio (HR) was 2.04 (95%CI;1.53–2.73). After adjusting for age, sex and baseline covariates, the HR was 1.85 (95% CI;1.37–2.52). After adjusting for age, sex, baseline covariates, and weighted time-dependent covariates, the HR was 1.63 (95% CI;1.07–2.50).
Conclusions Patients with a new diagnosis of SLE have 1.6 fold increased risk of HP than the general population. Given the impact of HP, this has important implications for mortality, functional status, and quality of life of people with SLE.
Funding Source(s): Canadian Institutes for Health Research (Grants MOP 125960 and THC 135235).
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