Method

This was a population-based, nationwide, cohort study. We included 74,771 from the Danish Multidisciplinary Hip Fractures Register (1) consisting of patients 65 years of age or older, who underwent surgery between January 1^st 2005 and December 31^st 2016 for all types of hip fracture. Cross-linkage with the Danish National Patient Register and The Danish Civil Registration system was made.

Demographic data extracted included vital status, civil status, gender, age, Body Mass Index (BMI), fracture classification (AO/OTA 31A-C) and surgical procedures binary registered as joint replacement or internal fixation, Charlson comorbidity index (CCI) and secondary diseases not included in CCI. Outcome was reoperations due to deep SSI in accordance with the definition from Centre for Disease Control (2). We computed cumulative incidence rates and risk ratios (RR) by calendar year periods and by different risk factors, considering death as competing risk and adjusting for age, gender, CCI, fracture type and surgery type.