A Systematic Review of Clinical Outcome Trajectories from 3 to 12 Months Following Mild or Moderate Traumatic Brain Injury

Our objective was to determine the extent to which clinical outcomes at 3 months predict the 6- to 12-month trajectory in people presenting with mild or moderate traumatic brain injury (TBI). We conducted a systematic review following Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines and searched MEDLINE, EMBASE, EBSCO, and the Web of Science Citation Index from 2005 until May 2025. All observational or interventional study designs that reported clinical outcomes in patients at 3 months, and at a later time point, following mild or moderate TBI were eligible for inclusion. Two authors independently selected and extracted data. Risk of bias was assessed using the Downs and Black checklist. Thirty studies (29 observational, 1 interventional) involving 7993 patients (7781 with mild TBI [mTBI]) met the inclusion criteria. Study quality was variable, and heterogeneity in study inclusion criteria and outcome reporting precluded meta-analyses and identification of patient and injury predictors of post 3-month outcome trajectory. Vulnerable populations-including older adults, those with pre-existing cognitive impairment, psychiatric illness, or intoxication-were frequently excluded. Analysis of the four most commonly reported outcome measures (Rivermead Post-Concussion Symptoms Questionnaire, Extended Glasgow Outcome Scale, Short Form 36 Health Survey, and Quality of Life after Brain Injury)-revealed symptom and functional improvement over time, particularly from hospital discharge to 3 months post-injury. However, substantial problems persist thereafter with 21-65% of patients continuing to experience symptoms or impairment, depending on cohort and outcome measure. The small number of patients with moderate TBI precluded comparison of outcomes to patients with mTBI. To improve clinical care, research, and patient experience, future targeted studies should identify factors determining the post-TBI outcome trajectory.