Multimorbidity Double Burden: Elevated Refracture Risk Despite High Mortality Following Fractures - A Linked Cohort Study.

Multimorbidity - defined as the presence of two or more chronic conditions - is highly prevalent among older adults with fractures and is associated with excess mortality; however, its impact on refracture risk remains uncertain. This study aimed to quantify refracture risk across different multimorbidity clusters and fracture sites, in order to identify high-risk individuals. A whole-of-population data linkage cohort study was conducted among adults aged 50 years and above living in New South Wales, Australia with at least one hospital or emergency admission between 1 January 2005 and 30 June 2022. Individuals who sustained a fracture between 1 January 2005 to 30 June 2021 were followed until 30 June 2022 for refracture and mortality outcomes. Latent class analysis (LCA) identified multimorbidity clusters. Fine-Gray subdistribution and Cox proportional hazards models estimated refracture and mortality risk. Among 335,308 individuals with fractures, 31.2% were men (mean [SD] age, 76.3 (10.7) years) and 68.8% were women (77.4 [10.7] years). Six clusters were identified: five multimorbidity clusters (cardiometabolic, cardiovascular, cancer, geriatric and mental health; median comorbidity count: 4-13) and one low multimorbidity cluster (median comorbidity count: 0). When compared to the general NSW population risk of incident fracture and death, all clusters demonstrated substantially higher refracture risk (HR range: 2.39-3.38 in men, 1.62-2.36 in women) despite high competing mortality (HR range: 1.58-4.52 in men, 1.13-3.08 in women). The mental health cluster carried the highest refracture burden, while distal fracture sites were associated with higher refracture risk due to lower mortality. Multimorbidity does not attenuate refracture risk; instead, it heightens vulnerability among older fracture patients, even in the presence of competing mortality. These findings reinforce the need for timely, targeted secondary fracture prevention, particularly following non-hip, non-vertebral fractures.