Following the PRISMA-P (Preferred Reporting Items for Systematic Review and Meta-Analysis Protocols) guidelines (Multimedia Appendix 1) [25], we outline an updated systematic review of quantitative and mixed methods studies reporting racial and/or ethnic differences in TBI outcomes across the lifespan. The systematic review protocol is registered in PROSPERO (CRD42023394529).

The PICOS (Patient, Intervention, Comparison, Outcomes, and Study Design) framework was used to develop our systematic review question and guide the development of the literature search strategies [26]. The elements are detailed below:

The Determinants of Inequities in Neurological Disease, Health, and Well-being framework by the National Institute of Neurological Disorders and Stroke will be used to also identify the individual-to-structural determinants of health reported in the included studies [21]

We have performed preliminary searches and piloted the study screening process using the CINAHL, Gale OneFile, PsycINFO (Ovid), and PubMed electronic databases to identify relevant quantitative or mixed method articles published in English. On January 9, 2023, we conducted a preliminary database search to ensure the inclusion of literature from January 1, 2009, to December 31, 2022. We recently conducted our final search on January 10, 2024, to identify relevant articles published since the last search through December 2023. We will hand search the reference lists of relevant systematic reviews and articles to identify additional studies not previously identified. All references identified through the searches will be exported into the online review software Covidence. Duplicates are removed automatically by the Covidence software.

A variety of Medical Subject Headings and relevant key words were developed and used by a medical librarian with significant experience in performing literature searches. The full search strategies for each database are included in Multimedia Appendix 2. Results were filtered by dates and English language.

Using Covidence, at least 2 of the 7 reviewers will independently screen each reference according to the title and abstract. All disagreements will be resolved either by the pair or by the inclusion of a third reviewer. During the initial preliminary search, we were able to identify 1746 records that were imported for screening (693 from CINAHL, 507 from PubMed, 326 from PsycINFO, and 220 from Gale OneFile). Of these, 520 duplicate references were automatically removed by Covidence. An additional 326 records were identified and added to Covidence (61 from CINAHL, 200 from PubMed, 21 from PsycINFO, and 44 from Gale OneFile) during the updated search through December 2023, and 103 duplicates were removed. We updated our search criteria to include Alaska Native, resulting in an additional 47 records identified (11 from CINAHL, 22 from PubMed, 10 from PsycINFO, and 4 from Gale OneFile). As a result, we added 12 additional abstracts after 35 duplicates were removed. We will begin the review of the 235 additional abstracts included. Upon abstract review completion and resolving any disagreements, we will begin the full-text screening phase. The full-text articles will be uploaded to Covidence to facilitate the review. Each full-text reference will be reviewed for inclusion by 2 independent reviewers out of the 7 total reviewers. Any disagreements will be resolved as a group. Full-text articles will be included in the data abstraction or collection phase. We will hand search the reference lists of relevant review articles that were flagged during the abstract and full-text screening phase, as well as review the references of the included full-text articles. We will also use hand searching methods to manually identify any relevant studies not identified through our included databases. A PRISMA (Preferred Reporting Items for Systematic Review and Meta-Analysis) flow diagram will document the selection process, including the reasons for exclusions.

The review team will meet to reflect on the full-text review process and included articles, then finalize the data extraction form and its elements for inclusion in Covidence. We will pilot test the data extraction form on at least 4 of the included articles before completing the process with the remaining included full-text articles. We will follow the same review process as before by having the reviewers work independently in pairs to extract data for each included article within Covidence. A third reviewer will resolve any discrepancies. If needed, the group will discuss the discrepancies to finalize the included data. If data are not clear in the article, the investigators will contact the authors to confirm.

The following data will be extracted from each of the included articles: source reference; publication year; population (ie, pediatric populations, adults aged ≥18 years, or older adults aged ≥55 years); race or ethnicity; sex or gender; geographic setting (eg, within or outside of the United States); study setting (eg, acute or inpatient, rehabilitation, outpatient, or community); sample characteristics; sample size; nature of study (descriptive, quantitative, or mixed methods); study design (eg, cross-sectional, cohort, or longitudinal); description and type of individual-, interpersonal-, institutional-, community-, or structural-level factors discussed (eg, socioeconomic status, health care coverage, housing, citizenship status, neighborhood location, or food security); measures of effect (eg, proportions, relative risks, odds ratios, or hazard ratios); outcome measures; and summary of author interpretations or conclusions.

Two investigators out of the 7 will independently assess the methodological quality of each individual article based on the Newcastle-Ottawa Quality Assessment Scale [27]. A third reviewer will address any disagreements, or the team will meet to discuss and decide as a group. If needed, study authors will be contacted to provide additional details or clarification.

Primary post-TBI outcomes include treatment outcomes (eg, emergency department, discharge disposition, rehabilitation placement or access, and rehabilitation treatment), mortality, functional outcomes (eg, functional status at admission, discharge, and 1+ years follow-up using the Functional Independence Measure, Disability Rating Scale, and Functional Status Examination instruments), psychosocial outcomes (eg, employment or productivity, community integration, marital status, quality of life or life satisfaction, and driving), cognitive or neuropsychological outcomes (eg, executive functioning, processing speed, and working memory), and emotional or neurobehavioral outcomes (eg, posttraumatic stress, postconcussion disorder, depression, anxiety, and aggression). Studies may also address as secondary outcomes those of caregivers of people with TBI (eg, caregiver burden, family functioning, psychological symptoms, posttraumatic stress disorder, and quality of life). However, if sufficient studies are identified based on caregiver outcomes, then we will report the findings in a separate review.

We plan to conduct a narrative synthesis instead of a meta-analysis due to the high likelihood of heterogeneity and the diversity of confounding variables and the data included in the studies. For the narrative synthesis, we will synthesize the types of studies, methodologies used, methodological considerations, findings of the studies (particularly regarding racial and ethnic differences in outcomes), evidence of findings, limitations of methods, and a summary of author conclusions. If sufficient data are identified, we will conduct a subgroup analysis by age (eg, older adults or pediatric populations) or by sex or gender.

No ethical approval from an institutional review board was required for this systematic review.

The goal of this work is to seek and review additional literature regarding outcomes of minoritized populations with TBI across the recovery process. Outcomes of interest are broad and inclusive of physical and cognitive functioning, as well as emotional and behavioral outcomes. This work will also review treatment outcomes in studies examining differences between minoritized and nonminoritized communities. This comprehensive review builds upon and updates decades-long research examining racial and ethnic disparities in TBI outcomes as the field continues to investigate ways to achieve health equity in the population with TBI.

This work is especially appropriate currently as many fields of research increase focus on SDoH [21,28], which affect all areas of a person’s environment, from education to health care access and quality, to economic stability and the social context. With the increased awareness and inclusion of SDoH in research since 2009, this review can contribute to the identification of higher-level intervention opportunities in terms of clinical and community programming, as well as policy changes affecting treatment across numerous points in the continuum of care. With this review, we expect to gain additional insight into progress or continuing barriers to health equity and be able to identify any gaps in the literature in the science of treatment and recovery for minoritized populations with TBI.

Limitations of our study include the use of only English-language studies, which can limit the representativeness of the review. Our study is also limited by the validity of the articles we include. The heterogeneity of the articles can make it difficult to draw conclusions; however, to facilitate interpretation, we will summarize the findings based on outcomes of interest. The definitions of race and ethnicity are informed socially and are continuously changing; these definitions could change in the future and alter the implications of our review. The treatment of racial and ethnic groups as homogenous could also lead to erroneous conclusions. We focused only on racial and ethnic social identities; therefore, we must acknowledge that there are multiple dimensions of social identities that may influence disparities in outcomes after TBI.

The results of this updated systematic review could provide greater insights into ethnic and racial disparities experienced following TBI across the lifespan. We hope that the results of this updated systematic review will not only corroborate the findings of Gary et al [14] and others, but also add to the knowledge base regarding post-TBI outcome differences by race or ethnicity. It will also include a comprehensive analysis of disparities across the various stages of recovery, outcomes, and settings and will use rigorous and systematic processes of review, data collection, and extraction. Instead of being one of many disparities-focused reviews, we hope that our findings will be serve as foundational knowledge to inform clinical practice; guide the development of patient-centered and culturally-guided services, programs, and interventions to address identified disparities; as well as to inform policy and practice changes to address systemic inequities that continue to perpetuate health disparities for marginalized communities with TBI.