Excess mortality following a first and subsequent osteoporotic fracture: a Danish nationwide register-based cohort study on the mediating effects of comorbidities

OBJECTIVES: This study aimed to examine the risk of mortality following incident and subsequent osteoporotic fractures, the effect of different fracture type combinations, and the mediating role of postfracture morbidity in a Danish population. METHODS: We used the National Patient Registry to identify patients ≥60 years with incident major osteoporotic fracture of the hip, vertebrae, wrist or humerus between 2013 and 2018, and controls matched 1:10 on age and sex. Possible mediators were identified using International Classification of Diseases, 10th Revision codes registered in the 6 months following index fracture. HRs were estimated using Cox regression analyses with 95% CIs. The effect of possible mediators was estimated using mediation analyses. RESULTS: The study included 106 303 patients and 1 062 988 controls. Mortality following index fracture was highest in the month following hip fractures (HR 10.98 (95% CI 10.23 to 11.79) in women and HR 16.40 (95% CI 15.00 to 17.93) in men). Subsequent hip fractures resulted in the highest HRs for all fracture type combinations. In women, the highest HR was observed in patients with index wrist/subsequent hip fractures (HR 2.43 (95% CI 2.12 to 2.78)). In men, the highest HR was observed in patients with index humerus/subsequent hip fractures (HR 2.69 (95% CI 2.04 to 3.54)). Pneumonia mediated the largest proportion of mortality, but dehydration, urinary tract infection and sepsis were also important factors. CONCLUSIONS: The highest mortality risk was found in the month immediately following both index and subsequent fracture. The combination of index and subsequent fractures at different skeletal sites had a substantial impact on the risk of mortality. Postfracture morbidities were found mediate the association.