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.