The Role of Comorbidity on Mortality after Hip Fracture: A Nationwide Norwegian Study of 38,126 Women with Hip Fracture Matched to a General Population Comparison Cohort.

Hip fracture patients often have comorbidities. We investigated whether the combination of comorbidity and hip fracture could explain the previously observed excess mortality among hip fracture patients compared to the general population. Using a population-based matched design with 38,126 Norwegian women suffering a hip fracture in the period 2009-2015 and the same number women in a matched comparison cohort, we matched on pre-fracture comorbidity, age, and education. We estimated relative survival, and additive and multiplicative comorbidity-hip fracture interaction. An additive comorbidity-hip fracture interaction of 4-9 per 100 patients was observed mainly during the first year after hip fracture. Among women with high comorbidity, 15 additional deaths per 100 patients were observed and of these, 9 deaths could be attributed to the interaction and 6 to the hip fracture per se. On the relative scale, we observed an increasing heterogeneity in survival by comorbidity over time; survival was reduced by around 40% after 6 years, among patients with high comorbidity while among women with no comorbidity, survival was reduced with 17% (hip fracture vs. no hip fracture). In summary, pre-fracture comorbidity was associated with short-term absolute excess mortality and long-term relative excess mortality.