Population-based, inception cohort study of the incidence, course, and prognosis of mild traumatic brain injury after motor vehicle collisions

Objective: To determine the incidence, course, and prognosis of adult mild traumatic brain injury (MTBI) caused by motor vehicle collisions.

Design: Prospective, population-based, inception cohort study.

Setting: The province of Saskatchewan, Canada, with a population of about 1,000,000 inhabitants.

Participants: All adults (N=1716) incurring an MTBI in a motor vehicle collision between November 1997 and December 1999 in Saskatchewan.

Interventions: Not applicable.

Main outcome measures: Age- and sex-stratified incidence rates, time to self-reported recovery, and prognostic factors over a 1-year follow-up.

Results: Of 7170 adults injured in a motor vehicle collision over the 2-year inception period, 1716 (24%) met our cohort definition of MTBI. There were more women affected (53%), and MTBI was most common in the 18- to 23-year-old group. Most were not hospitalized (73%), but 28% reported loss of consciousness and 23% reported posttraumatic amnesia. The annual incidence of MTBI per 100,000 adults was 106.1 (95% confidence interval [CI], 98.9-113.6) in the first year and 118.3 (95% CI, 110.8-126.3) in the second year of the study. The 1-year follow-up rate was 84%. The median time to recovery was 100 days (95% CI, 97-103), and about 23% reported not having recovered by 1 year. Factors associated with delayed recovery included being older than 50 years, having less than a high school education, having poor expectations for recovery, having depressive symptoms, having arm numbness, having hearing problems, having headaches, having low back pain, and having thoracic back pain. Loss of consciousness and posttraumatic amnesia were not associated with recovery.

Conclusions: MTBI affects almost a quarter of persons reporting an injury after a traffic collision. The median time to recovery is 100 days, but 23% have still not recovered by 1 year. A mix of biopsychosocial factors is associated with recovery, including a strong effect of poor expectations for recovery.