The role of pre-existing comorbidity on the rate of recovery following injury: A longitudinal cohort study.

Understanding the role of comorbidity in recovery following injury is an important challenge given the increasing prevalence of multimorbidity (2 or more comorbidities) in many countries. The Prospective Outcomes of Injury Study recruited 2856 injured 18-64 year olds that had registered for entitlements with New Zealand's universal no-fault injury insurer. Recovery, or lack of, in this longitudinal cohort was measured using the World Health Organization Disability Assessment Schedule at 3, 12 and 24 months post-injury. Twenty-one pre-existing chronic conditions were used to identify comorbidity. To investigate whether rates of recovery differed by pre-injury comorbidity, the interaction between time and comorbidity was modelled using Generalised Estimating Equations. Of 1,862 participants with complete data, the distribution reporting none, one comorbidity, or multimorbidity pre-injury was 51%, 27%, and 21% respectively. Longitudinal analysis estimated no difference (log odds per year 0.05, 95% Confidence Interval -0.17 to 0.27) between the rate of change of disability for those with one pre-injury comorbidity compared to those with none. Those with pre-injury multimorbidity had significantly slower reduction in disability over time than those with no pre-injury comorbidity (log odds per year 0.27, 95% Confidence Interval 0.05 to 0.48). In a working age cohort, the rate of recovery in the 24 months following injury was similar for those with none or one pre-existing comorbidity and significantly slower for those with multimorbidity. It is important that further research explores mechanisms driving this, and that researchers and health providers identify and implement better supports for injured people with multimorbidity.