Current Trends in Comorbidity Prevalence and Associated Mortality in a Population-Based Cohort of Hip Fracture Patients in Denmark

Pia Kjær Kristensen,1,2 Thomas Johannesson Hjelholt,3,4 Morten Madsen,3 Alma B Pedersen2,3 1Department of Orthopedic Surgery, Aarhus University Hospital, Aarhus, Denmark; 2Department of Clinical Medicine, Aarhus University, Aarhus, Denmark; 3Department of Clinical Epidemiology, Aarhus University Hospital, Aarhus, Denmark; 4Department of Internal Medicine, Viborg Regional Hospital, Viborg, DenmarkCorrespondence: Pia Kjær Kristensen, Department of Orthopedic Surgery, Aarhus University Hospital, Palle Juul-Jensens Boulevard 165, Aarhus, 8200, Denmark, Tel +45 78454111, Email pkkr@clin.au.dkBackground and Purpose: Patients with hip fractures often have comorbidities, but detailed data on comorbidity and its impact on prognosis are lacking. We described the current trends in the prevalence of comorbidity and the magnitude of the associated mortality.Patients and Methods: From the Danish Multidisciplinary Hip Fracture Registry we included 31,443 hip fracture patients (diagnosed in 2014– 2018). We calculated the prevalence of individual diseases and comorbidity measured with the Charlson Comorbidity Index (CCI), the Elixhauser Index, and the Rx-Risk Index. We calculated sex and age-adjusted odds ratios (aORs) for 30-day mortality and hazard ratios (aHRS) for one-year mortality with 95% confidence intervals (CI).Results: The most common diseases identified with the CCI were cerebrovascular diseases (18%), malignancies (17%), chronic pulmonary disease (14%), and dementia (11%). Using the Elixhauser Index, hypertension (37%), cardiac arrhythmias (21%), and fluid and electrolyte disorders (15%) were most prevalent, while ischemic heart disease (42%), hypertension (39%), and use of antiplatelets (37%) were most prevalent when using the Rx-Risk Index. Using the Rx-Risk Index, only 28% of patients had no comorbidity compared to 38% for CCI and 44% for the Elixhauser Index, and the prevalence was stable through the years. Compared to patients with no comorbidity, patients with very severe comorbidity had an aORs for 30-day mortality of 2.6 (CI: 2.4– 2.9) using CCI, 2.6 (CI: 2.4– 3.1) using the Elixhauser Index, and 3.1 (CI: 2.7– 3.4) using the Rx-Risk Index.Interpretation: More than 50% of the patients with hip fractures have moderate to very severe comorbidity, with considerable variation between indices. The prevalence of individual diseases varies considerably. All indices had comparable dose-response associations with mortality. These results are relevant for clinicians to amend prevention and target care, and for researchers to decide which comorbidity measure to use depending on the research question.Keywords: Charlson Comorbidity Index, comorbidity, Elixhauser Index, hip fracture, mortality, Rx-Risk