The incidence of subsequent contralateral hip fracture and factors associated with increased risk: the IMPACT Contralateral Fracture Study

Summary
Patients who sustain a contralateral hip fracture experience significantly inferior outcomes; however, the incidence and predictors of contralateral hip fracture remain poorly understood. In the present study, 2.5% of patients sustained a contralateral hip fracture within 12 months, and socioeconomic deprivation was associated with reduced risk of contralateral hip fracture.

Introduction
Hip fractures are associated with high morbidity and mortality, and patients that sustain a subsequent contralateral fracture experience inferior outcomes. The risk of contralateral fracture is highest within the first year; however, the incidence and associated factors remain poorly understood. The aims were to investigate (i) the incidence of a subsequent contralateral hip fracture within the first year, (ii) identify factors associated with an increased risk of contralateral fracture and (iii) compare early mortality risk after index versus contralateral hip fracture.

Methods
This study included all patients aged over 50 years admitted to NHS hospitals in Scotland between 1st March 2020 and 31st December 2020 (n = 5566) as routine activity of the Scottish Hip Fracture Audit (SHFA). Multivariate logistic regression was used to examine factors associated with 30-day mortality, and cox regression was used to identify factors associated with a contralateral fracture.

Results
During the study period 2.5% (138/5566) of patients sustained a contralateral hip fracture within 12 months of the index hip fracture. Socioeconomic deprivation was inversely associated with increased risk of contralateral fracture (odds ratio 2.64, p < 0.001), whilst advancing age (p = 0.427) and sex (p = 0.265) were not. After adjusting for significant cofounders, there was no significant difference in 30-day mortality following contralateral fracture compared to index fracture (OR 1.22, p = 0.433).

Conclusion
One in 40 (2.5%) hip fracture patients sustained a contralateral fracture within 12 months of their index fracture, and deprivation was associated with a reduced risk of contralateral fracture. No difference in 30-day mortality was found.