Background Traumatic brain injury (TBI) is extremely common in children, with approximately 500,000 cases attending hospital in the UK each year. Over 90% are considered mild and most children recover well. However, some have persistent symptoms, though relatively few are diagnosed as post-concussion syndrome (PCS). TBI, and particularly repeated TBI, is increasingly associated with poor outcomes in adulthood. Poor post-injury symptom pattern recognition impedes the development of interventions to prevent PCS.

Objective To identify factors associated with long- term adverse outcomes in children after mild traumatic brain injury (mTBI) to inform recommendations for research.

Methods Using published methods for scoping reviews, we identified observational studies reporting demographic, premorbid and injury-related factors, or bio-marker risk factors, for adverse outcomes 3 months or longer after mTBI in children under 18 years. We searched Medline, EMBASE and CINAHL and the reference lists of included studies and systematic reviews up to January 2022. Titles, abstracts and full texts were screened in duplicate and data extraction completed by one author. Risk factors were tabulated for outcomes (i) PCS (ii) recovery. Following scoping review methods, effect estimates were not pooled and included studies not assessed for bias.

Results Forty-nine risk factors for 12 different outcomes were reported in 73 included studies. Risk factors most commonly assessed were sex (n=28), age (n=23), injury mechanism (n=22) and prior mTBI (n=18). Wider determinants known to influence health and behaviour (e.g. socioeconomic status) were seldom studied. Twelve studies reported PCS outcomes and 29 reported recovery outcomes. Additional outcomes studied were symptom scores/severity (n=22), quality of life (n=9) and cognitive function (n=9). The associations between any of the risk factors and adverse outcomes were inconsistent.

Conclusions Variable definitions of ‘mild’ TBI and severity thresholds may have contributed to the inconsistent findings and suggest consensus on definitions would be helpful. The most studied outcomes (recovery patterns and symptom severity) may not be the most important for clinicians or patients. To enable reliable prediction of children at risk of poor outcomes following mTBI, future primary studies should be prospective, population-based, address pre-specified hypotheses and include long term follow up of patient-important outcomes.

Theme social determinants.