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Full-face motorcycle helmets to reduce injury and death: A systematic review, meta-analysis, and practice management guideline from the Eastern Association for the Surgery of Trauma

      Highlights

      • Full-face helmets significantly reduce traumatic brain injury.
      • Full-face helmets significantly reduce facial fracture.
      • Full-face helmets reduce severity of head, neck, and facial injury.

      Abstract

      Background

      While motorcycle helmets reduce mortality and morbidity, no guidelines specify which is safest. We sought to determine if full-face helmets reduce injury and death.

      Methods

      We searched for studies without exclusion based on: age, language, date, or randomization. Case reports, professional riders, and studies without original data were excluded. Pooled results were reported as OR (95% CI). Risk of bias and certainty was assessed. (PROSPERO #CRD42021226929).

      Results

      Of 4431 studies identified, 3074 were duplicates, leaving 1357 that were screened. Eighty-one full texts were assessed for eligibility, with 37 studies (n = 37,233) eventually included. Full-face helmets reduced traumatic brain injury (OR 0.40 [0.23–0.70]); injury severity for the head and neck (Abbreviated Injury Scale [AIS] mean difference −0.64 [-1.10 to −0.18]) and face (AIS mean difference −0.49 [-0.71 to −0.27]); and facial fracture (OR 0.26 [0.15–0.46]).

      Conclusion

      Full-face motorcycle helmets are conditionally recommended to reduce traumatic brain injury, facial fractures, and injury severity.

      Graphical abstract

      Keywords

      1. Introduction

      Helmets mitigate excess morbidity and mortality from motorcycle collisions, which are over-represented in road traffic injuries.
      • Liu B.C.
      • Ivers R.
      • Norton R.
      • et al.
      Helmets for preventing injury in motorcycle riders.
      ,
      • WHO
      Global Status Report on Road Safety 2018.
      Injury prevention experts recommend universal helmet use but helmet type is not specified.
      • MacLeod J.B.
      • Digiacomo J.C.
      • Tinkoff G.
      An evidence-based review: helmet efficacy to reduce head injury and mortality in motorcycle crashes: EAST practice management guidelines.
      However, a recent scoping review identified helmet type as an important injury prevention intervention, particularly for head and neck injuries.
      • Tabary M.
      • Ahmadi S.
      • Amirzade-Iranaq M.H.
      • et al.
      The effectiveness of different types of motorcycle helmets - a scoping review.
      Nevertheless, no evidence-based guideline currently exists. Prior systematic reviews on the subject have methodological limitations, including: age- or language-restricted queries, use of outdated PRISMA guidelines, or search strategies with limitations in sensitivity (i.e. missing studies) or scope (i.e. missing grey literature or exclusion due to missing full text).
      • Lucci C.
      • Piantini S.
      • Savino G.
      • Pierini M.
      Motorcycle helmet selection and usage for improved safety: a systematic review on the protective effects of helmet type and fastening.
      • Chaichan S.
      • Asawalertsaeng T.
      • Veerapongtongchai P.
      • et al.
      Are full-face helmets the most effective in preventing head and neck injury in motorcycle accidents? A meta-analysis.
      • Higgins J.P.T.
      • Thomas J.
      • Chandler J.
      • et al.
      Cochrane Handbook for Systematic Reviews of Interventions: Cochrane.
      • Cavalcante D.K.F.
      • Veloso S.R.M.
      • Durao M.A.
      • et al.
      Do helmet use and type influence facial trauma occurrence and severity in motorcyclists? A systematic review and meta-analysis.
      Thus, the Eastern Association for the Surgery of Trauma Guidelines Committee Injury Prevention Task Force sought to develop a practice management guideline on the use of full-face motorcycle helmets using the previously validated Grading of Recommendations Assessment, Development and Evaluation (GRADE) methodology.
      • Guyatt G.H.
      • Oxman A.D.
      • Vist G.E.
      • et al.
      GRADE: an emerging consensus on rating quality of evidence and strength of recommendations.
      ,
      • Kerwin A.J.
      • Haut E.R.
      • Burns J.B.
      • et al.
      The eastern association of the Surgery of trauma approach to practice management guideline development using grading of recommendations, assessment, development, and evaluation (GRADE) methodology.

      1.1 Objectives

      The objective was to evaluate whether use of full-face helmets versus helmets that are not full-face among non-professional motorcycle riders reduces risk of injury and death and generate a recommendation based on the results. The GRADE approach utilizes a priori creation of questions in the Population, Intervention, Comparator, Outcomes (PICO) format. The review was conducted in accordance with Cochrane methodological expectations.
      • Higgins J.P.T.
      • Lasserson T.
      • Chandler J.
      • et al.
      Methodological Expectations of Cochrane Intervention Reviews.
      This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. This study was registered with the International Prospective Register of Systematic Reviews (PROSPERO #CRD42021226929).

      1.2 PICO question

      Before a literature search, a Population, Intervention, Comparator (PICO) question was formulated with working group consensus: Should non-professional motorcycle riders (P) wear full-face helmets (I) versus helmets that are not full-face (C) to reduce the risk of mortality; injury severity (of the head, face, and neck); traumatic brain injury (TBI); cervical spinal cord injury (SCI); cervical spine fracture; blunt cerebrovascular injury; or facial fracture (O)?

      1.3 Selection of outcome measures

      Working group members then independently voted on numerous candidate outcomes via an electronic, modified Delphi process, on a scale of 1–9. The top 7 critical
      • Higgins J.P.T.
      • Thomas J.
      • Chandler J.
      • et al.
      Cochrane Handbook for Systematic Reviews of Interventions: Cochrane.
      • Cavalcante D.K.F.
      • Veloso S.R.M.
      • Durao M.A.
      • et al.
      Do helmet use and type influence facial trauma occurrence and severity in motorcyclists? A systematic review and meta-analysis.
      • Guyatt G.H.
      • Oxman A.D.
      • Vist G.E.
      • et al.
      GRADE: an emerging consensus on rating quality of evidence and strength of recommendations.
      and important
      • Tabary M.
      • Ahmadi S.
      • Amirzade-Iranaq M.H.
      • et al.
      The effectiveness of different types of motorcycle helmets - a scoping review.
      • Lucci C.
      • Piantini S.
      • Savino G.
      • Pierini M.
      Motorcycle helmet selection and usage for improved safety: a systematic review on the protective effects of helmet type and fastening.
      • Chaichan S.
      • Asawalertsaeng T.
      • Veerapongtongchai P.
      • et al.
      Are full-face helmets the most effective in preventing head and neck injury in motorcycle accidents? A meta-analysis.
      outcomes were included.
      • Higgins J.P.T.
      • Thomas J.
      • Chandler J.
      • et al.
      Cochrane Handbook for Systematic Reviews of Interventions: Cochrane.
      Outcomes with a score <4 were deemed of limited importance and not included. Candidate outcomes and their scores are summarized in Supplementary Table 1.

      2. Material and methods

      2.1 Study types

      Only randomized controlled trials (RCTs), prospective and retrospective observational studies, case-control studies, and cross-sectional surveys that included both subjects receiving the intervention and comparator were eligible for inclusion. Both peer-reviewed and grey literature were considered.
      • Higgins J.P.T.
      • Thomas J.
      • Chandler J.
      • et al.
      Cochrane Handbook for Systematic Reviews of Interventions: Cochrane.
      ,
      • Higgins J.P.T.
      • Lasserson T.
      • Chandler J.
      • et al.
      Methodological Expectations of Cochrane Intervention Reviews.
      Case series and reports, commentaries, reviews, animal studies, laboratory studies, studies containing no original data or analyses, editorials, letters, and opinion articles were excluded. No limitations were placed on year or language.

      2.2 Participant types

      All relevant studies of non-professional motorcycle riders were eligible inclusive of age, race, ethnicity, sex, and other demographic characteristics, including seating position, study country, and purpose of use, such as transportation, recreational, or commercial. Studies of racing and off-road motorcycling were excluded.

      2.3 Intervention types

      Full-face helmets were defined as helmets that cover the full head, including base of skull posteriorly, and the face, including the cheeks and the lower face via a fixed chin bar. Helmets that are not full-face vary. An open-face helmet, also known as a ¾ helmet, lacks a chin bar but still covers the full head. A half helmet covers neither the face nor the base of the skull.
      A modular helmet has an articulating chin bar that can convert the helmet between full- and open-face. Because of possible crossover, this helmet was excluded. Novelty helmets do not meet materials or design standards and were also excluded.

      2.4 Outcome measure types

      Studies were included if they reported the outcomes of interest defined by the PICO question. Abbreviated Injury Scale (AIS) was selected to report injury severity.

      2.5 Search strategy

      A health science librarian conducted a systematic search of: Ovid MEDLINE, Elsevier Embase, Cochrane CENTRAL, CINAHL, SPORTDiscus, Scopus, Web of Science, and Engineering Village. The search strategy was written for MEDLINE and translated using each database's syntax and controlled vocabulary. No limits, filters, or hedges were used. The search strategy was adapted in part with the Institute for Evidence Based Healthcare's Polyglot Search translator.
      • Clark J.M.
      • Sanders S.
      • Carter M.
      • et al.
      Improving the translation of search strategies using the Polyglot Search Translator: a randomized controlled trial.
      Database subject headings and text words were used for motorcycle helmets, helmet types, and their synonyms. The search strategy was peer-reviewed using the Peer Review for Electronic Search Strategies (PRESS) tool (Appendix 1).
      • Rethlefsen M.L.
      • Kirtley S.
      • Waffenschmidt S.
      • et al.
      PRISMA-S: an extension to the PRISMA statement for reporting literature searches in systematic reviews.
      ,
      • McGowan J.
      • Sampson M.
      • Salzwedel D.M.
      • et al.
      PRESS peer review of electronic search strategies: 2015 guideline statement.
      A manual reference list search of relevant scoping and systematic reviews and included studies supplemented the database queries. An initial search was completed on December 23, 2020 and a second on November 6, 2021. An initial reference list search was completed on September 26, 2021 and a second on November 8, 2021. In total, 4431 abstracts were identified and 3074 duplicates were automatically removed by Covidence (Covidence, Melbourne, Australia) leaving 1357 abstracts for review.

      2.6 Study selection

      Abstracts were independently screened by two working group members. Of these, 81 studies were selected for possible inclusion. Full texts were independently reviewed by two team members and by first and senior authors. Any disagreement was adjudicated by one of the working group's two GRADE-trained methodologists. At this stage, 44 studies were excluded (Supplementary Table 2), with reasons summarized in a PRISMA 2020 flow diagram (Fig. 1).
      • Page M.J.
      • McKenzie J.E.
      • Bossuyt P.M.
      • et al.
      The PRISMA 2020 statement: an updated guideline for reporting systematic reviews.
      Retraction Watch and journal websites of included studies were reviewed to ensure no studies had been retracted.

      Oransky I, Marcus A. Retraction Watch [updated November 2021November 2, 2021]. Available from: https://retractionwatch.com.

      Thus, 37 studies were included.
      Fig. 1
      Fig. 1PRISMA flow diagram
      * Results separated by first and second search.

      2.7 Data extraction and management

      Data were extracted in duplicate in Excel (Microsoft, Redmond, WA) and meta-analyses were completed using Review Manager (Cochrane Collaboration, London, England). The working group chose to preferentially pool adjusted odds ratios over unadjusted event rates. When data that could be potentially included in a meta-analysis were not able to extracted based on published data alone, raw data was requested from the corresponding author. Statistical significance was set at p < 0.05. The Mantel-Haenszel method was used to calculate pooled odds ratios (95% confidence intervals) for dichotomous outcomes and the DerSimonian and Laird inverse variance method was used to calculate pooled mean differences (95% confidence intervals) for continuous outcomes. Random effects modeling was utilized for both outcome types. Heterogeneity was quantified with I2, explored with sensitivity analyses, and stratified: 0–40% may not be important, 30–60% may represent moderate heterogeneity, 50–90% may represent substantial heterogeneity, and 75–100% represents considerable heterogeneity.
      • Higgins J.P.T.
      • Thomas J.
      • Chandler J.
      • et al.
      Cochrane Handbook for Systematic Reviews of Interventions: Cochrane.
      Interpretations were then shared through email and conference calls with no major reviewer discrepancies.

      2.8 Methodological quality assessment

      The quality of each study was independently assessed by a working group member and at least the first or senior author using GRADEpro (Evidence Prime, Inc., Hamilton, Ontario, Canada). Each reviewer graded studies for effect size, risk of bias, inconsistency, indirectness, imprecision, and publication bias. Large effect was defined as OR <0.5 or OR >2.0 for purposes of upgrading.
      • Higgins J.P.T.
      • Thomas J.
      • Chandler J.
      • et al.
      Cochrane Handbook for Systematic Reviews of Interventions: Cochrane.
      Publication bias was assessed with funnel plots.
      A recommendation was generated based on the findings, quality of the evidence, benefits and harms, patient values and preferences, resource utilization, and feasibility. Peer-reviewed data on patient values and preferences were supplemented with expert opinion from academic acute care surgeons who identify as part of different motorcycle subcultures and regularly ride. Strong recommendations are based on moderate- or high-quality evidence and are phrased, “We recommend.” Weak recommendations are based on low- or very low-quality evidence and are phrased, “We conditionally recommend.”
      • Kerwin A.J.
      • Haut E.R.
      • Burns J.B.
      • et al.
      The eastern association of the Surgery of trauma approach to practice management guideline development using grading of recommendations, assessment, development, and evaluation (GRADE) methodology.

      3. Results

      3.1 PICO 1: should non-professional motorcycle riders wear full-face helmets vs helmets that are not full-face to reduce the risk of mortality; injury severity (of the head, face, and neck); traumatic brain injury (TBI); cervical spinal cord injury (SCI); cervical spine fracture; blunt cerebrovascular injury; or facial fracture?

      There were no randomized and 37 non-randomized studies included, comprising 37,233 subjects (Table 1).
      • Arif M.Z.
      • B R.R.
      • Prasad K.
      The role of helmet fastening in motorcycle road traffic accidents.
      • Brewer B.L.
      • Diehl 3rd, A.H.
      • Johnson L.S.
      • et al.
      Choice of motorcycle helmet makes a difference: a prospective observational study.
      • Cannell H.
      • King J.B.
      • Winch R.D.
      Head and facial injuries after low-speed motor-cycle accidents.
      • Capewell S.
      • Reece V.A.
      • Milne D.D.
      Motorcyclists should be encouraged to wear full face crash helmets.
      • Cavalcante J.R.
      • Oka S.C.
      • de Santana Santos T.
      • et al.
      Influence of helmet use in facial trauma and moderate traumatic brain injury victims of motorcycle accidents.
      • Chiu W.T.
      • Kuo C.Y.
      • Hung C.C.
      • Chen M.
      The effect of the Taiwan motorcycle helmet use law on head injuries.
      • Cini M.A.
      • Prado B.G.
      • Hinnig Pde F.
      • et al.
      Influence of type of helmet on facial trauma in motorcycle accidents.
      • Erhardt T.
      • Rice T.
      • Troszak L.
      • Zhu M.
      Motorcycle helmet type and the risk of head injury and neck injury during motorcycle collisions in California.
      • Hitosugi M.
      • Shigeta A.
      • Takatsu A.
      • et al.
      Analysis of fatal injuries to motorcyclists by helmet type.
      • Lam C.
      • Wiratama B.S.
      • Chang W.H.
      • et al.
      Effect of motorcycle helmet types on head injuries: evidence from eight level-I trauma centres in Taiwan.
      • Lin M.R.
      • Tsauo J.Y.
      • Hwang H.F.
      • et al.
      Relation between motorcycle helmet use and cervical spinal cord injury.
      • Liu C.H.
      104 the injury severity of the face, head and neck of motorcyclists in different types of helmets during motor vehicle accidents.
      • Liu C.H.
      • Huang Y.C.
      319: the relationship between facial bone fractures with accompanied injuries and the helmet types of the motorcyclists in traffic accidents.
      • Lopes Albuquerque C.E.
      • Nogueira Arcanjo F.P.
      • Cristino-Filho G.
      • et al.
      How safe is your motorcycle helmet?.
      • McIntyre A.
      • Nieuwesteeg M.
      • Cockfield S.
      Motorcyclist Injuries and Protective Clothing: Research with TAC Clients.
      • Moshy J.R.
      • Msemakweli B.S.
      • Owibingire S.S.
      • Sohal K.S.
      Pattern of mandibular fractures and helmet use among motorcycle crash victims in Tanzania.
      • O'Connor P.J.
      Motorcycle helmets and spinal cord injury: helmet usage and type.
      • O'Connor P.J.
      • Kloeden C.
      • McLean A.J.
      Do full-face helmets offer greater protection against cervical spinal cord injury than open-face helmets?.
      • Porto G.G.
      • de Menezes L.P.
      • Cavalcante D.K.F.
      • et al.
      Do type of helmet and alcohol use increase facial trauma severity?.
      • Ramli R.
      • Oxley J.
      Motorcycle helmet fixation status is more crucial than helmet type in providing protection to the head.
      • Ramli R.
      • Oxley J.
      • Hillard P.
      • et al.
      The effect of motorcycle helmet type, components and fixation status on facial injury in Klang Valley, Malaysia: a case control study.
      • Rice T.M.
      • Troszak L.
      • Erhardt T.
      • et al.
      Novelty helmet use and motorcycle rider fatality.
      • Sung K.M.
      • Noble J.
      • Kim S.C.
      • et al.
      The preventive effect of head injury by helmet type in motorcycle crashes: a rural Korean single-center observational study.
      • Tripathi M.
      • Tewari M.K.
      • Mukherjee K.K.
      • Mathuriya S.N.
      Profile of patients with head injury among vehicular accidents: an experience from a tertiary care centre of India.
      • Tsai Y.J.
      • Wang J.D.
      • Huang W.F.
      Case-control study of the effectiveness of different types of helmets for the prevention of head injuries among motorcycle riders in Taipei, Taiwan.
      • Vaughan R.G.
      Motor cycle helmets and facial injuries.
      • Wong S.L.
      • Liu C.H.
      • Huang Y.C.
      Assessing the facial, head and neck injuries of motorcyclists in various types of helmets during motor vehicle crashes using the abbreviated injury scale.
      • Wu D.
      • Dufournet M.
      • Martin J.L.
      Does a full-face helmet effectively protect against facial injuries?.
      • Yadukul S.
      • Devadass P.K.
      • Gururaj G.
      Role of helmet in preventing head injury among two wheeler occupants in fatal road traffic injuries.
      • Yeo J.D.
      Five-year review of spinal cord injuries in motorcyclists.
      • Yokoyama T.
      • Kawamata H.
      • Hitosugi M.
      • et al.
      Relationship between the severity of oral and maxillofacial injuries and helmet use by type in motorcycle accidents.
      • Yu W.Y.
      • Chen C.Y.
      • Chiu W.T.
      • Lin M.R.
      Effectiveness of different types of motorcycle helmets and effects of their improper use on head injuries.
      • Abhinandan Patel K.N.
      • Sneha T.R.
      • Reddy K.R.
      • et al.
      Changing trends in the pattern of maxillofacial injuries in helmeted motorcycle accident patients when compared to non-helmeted motorcycle accident patients.
      • Colangeli W.
      • Cordaro R.
      • Boschetti C.E.
      • et al.
      Protective effects of helmet type on facial injuries.
      • Brasileiro B.F.
      • Vieira J.M.
      • da Silveira C.E.S.
      Avaliação de traumatismos faciais por acidentes motociclísticos em Aracaju/SE.
      • Rocchi G.
      • Fadda M.T.
      • Marianetti T.M.
      • et al.
      Craniofacial trauma in adolescents: incidence, etiology, and prevention.
      • Usha M.
      • Ravindran V.
      • Soumithran C.S.
      • Ravindran Nair K.S.
      The impact of mandatory helmet law on the outcome of maxillo facial trauma: a comparative study in Kerala.
      The non-randomized studies consisted of: 8 prospective observational, 16 retrospective cohort, 2 before-and-after, 7 retrospective case-control, and 4 cross-sectional survey studies. Thirty-two studies were peer-reviewed and 5 were grey literature, including conference abstracts, industry or government reports, and unpublished studies. Eighteen studies were suitable for meta-analysis, with each study result reported in Fig. 2.
      • Arif M.Z.
      • B R.R.
      • Prasad K.
      The role of helmet fastening in motorcycle road traffic accidents.
      • Brewer B.L.
      • Diehl 3rd, A.H.
      • Johnson L.S.
      • et al.
      Choice of motorcycle helmet makes a difference: a prospective observational study.
      • Cannell H.
      • King J.B.
      • Winch R.D.
      Head and facial injuries after low-speed motor-cycle accidents.
      ,
      • Cavalcante J.R.
      • Oka S.C.
      • de Santana Santos T.
      • et al.
      Influence of helmet use in facial trauma and moderate traumatic brain injury victims of motorcycle accidents.
      ,
      • Hitosugi M.
      • Shigeta A.
      • Takatsu A.
      • et al.
      Analysis of fatal injuries to motorcyclists by helmet type.
      ,
      • Liu C.H.
      104 the injury severity of the face, head and neck of motorcyclists in different types of helmets during motor vehicle accidents.
      • Liu C.H.
      • Huang Y.C.
      319: the relationship between facial bone fractures with accompanied injuries and the helmet types of the motorcyclists in traffic accidents.
      • Lopes Albuquerque C.E.
      • Nogueira Arcanjo F.P.
      • Cristino-Filho G.
      • et al.
      How safe is your motorcycle helmet?.
      ,
      • Moshy J.R.
      • Msemakweli B.S.
      • Owibingire S.S.
      • Sohal K.S.
      Pattern of mandibular fractures and helmet use among motorcycle crash victims in Tanzania.
      • O'Connor P.J.
      Motorcycle helmets and spinal cord injury: helmet usage and type.
      • O'Connor P.J.
      • Kloeden C.
      • McLean A.J.
      Do full-face helmets offer greater protection against cervical spinal cord injury than open-face helmets?.
      ,
      • Rice T.M.
      • Troszak L.
      • Erhardt T.
      • et al.
      Novelty helmet use and motorcycle rider fatality.
      ,
      • Vaughan R.G.
      Motor cycle helmets and facial injuries.
      ,
      • Wong S.L.
      • Liu C.H.
      • Huang Y.C.
      Assessing the facial, head and neck injuries of motorcyclists in various types of helmets during motor vehicle crashes using the abbreviated injury scale.
      ,
      • Yeo J.D.
      Five-year review of spinal cord injuries in motorcyclists.
      ,
      • Yokoyama T.
      • Kawamata H.
      • Hitosugi M.
      • et al.
      Relationship between the severity of oral and maxillofacial injuries and helmet use by type in motorcycle accidents.
      ,
      • Brasileiro B.F.
      • Vieira J.M.
      • da Silveira C.E.S.
      Avaliação de traumatismos faciais por acidentes motociclísticos em Aracaju/SE.
      ,
      • Usha M.
      • Ravindran V.
      • Soumithran C.S.
      • Ravindran Nair K.S.
      The impact of mandatory helmet law on the outcome of maxillo facial trauma: a comparative study in Kerala.
      Reporting of adjusted odds ratios was too sparse to use generic inverse variance for meta-analyses. Thus, unadjusted event rates were pooled to create summary statistics. For two studies in which published data could not be extracted, corresponding authors were contacted for raw data, but neither were able to provide additional data.
      • Amirjamshidi A.
      • Ardalan A.
      • Nainei K.H.
      • et al.
      Comparison of standard and nonstandard helmets and variants influencing the choice of helmets: a preliminary report of cross-sectional prospective analysis of 100 cases.
      ,
      • Arif M.Z.
      • Rajanikanth B.R.
      • Prasad K.
      Soft tissue injuries of the maxillofacial region occurring from motorcycle accidents.
      Sources of funding were able to be identified for 25 studies, with none demonstrating a potential for bias. Funnel plots created for each outcome did not reveal publication bias. The quality of evidence was very low, with risk of bias, inconsistency, and imprecision. Even so, large effect size of intervention was demonstrated for TBI and facial fracture, upgrading their evidence quality to low.
      Table 1Characteristics of included studies.
      ReferenceMethodsPeer reviewedParticipants & settingOutcomesEvidence grade
      Abhinandan Patel 2021Cross-sectional surveyYesn = 741, urban faciomaxillary trauma surgery service, India, adultsFacial fracture, facial injury severityLow
      Arif 2019Prospective observationalYesn = 311, urban ED, India, no age restrictionFacial fractureLow
      Brasileiro 2010Prospective observationalYesn = 145, urban ED, Brazil, no age restrictionFacial fractureLow
      Brewer 2013Prospective observationalYesn = 151, urban ED, USA, no age restrictionMortality, TBI,

      C-spine/facial fracture
      Low
      Cannell 1982Retrospective cohortYesn = 56, urban accident registry, UK, no age restrictionH&N, facial injury severityVery low
      Capewell 1984Retrospective cohortNon = 194, urban ED, UK, no age restrictionH&N injuryVery low
      Cavalcante 2012Prospective observationalYesn = 272, urban ED patients with moderate TBI, Brazil, no age restrictionFacial fractureLow
      Chiu 2000Before-and-after studyYesn = 8795, national trauma registry, Taiwan, no age restrictionTBIVery low
      Cini 2014Retrospective case-controlYesn = 157, urban ED patients with isolated facial trauma, Brazil, no age restrictionH&N, facial injury severityVery low
      Colangeli 2021Retrospective cohortYesn = 287, urban maxillofacial department, Italy, adultsFacial injury severityLow
      Erhardt 2016Retrospective cohortYesn = 7545, police crash registry, USA, adultsH&N injuryVery low
      Hitosugi 2004Retrospective cohortYesn = 36, suburban autopsies, Japan, adultsH&N injury severity

      C-spine fracture
      Low
      Lam 2020Cross-sectional surveyYesn = 725, 8 trauma center survivors to discharge, Taiwan, adultsH&N injuryVery low
      Lin 2004Retrospective case-controlYesn = 147, national trauma registry, Taiwan, no age restrictionC-spine SCIVery low
      Liu 2007Retrospective cohortNon = 115, urban hospital trauma registry, no age restriction, TaiwanTBI, facial fractureVery low
      Liu 2012Prospective observationalNon = 127, urban ED, Taiwan, no age restrictionH&N, facial injury severityVery low
      Lopes-Albuquerque 2014Retrospective cohortYesn = 253, urban ED discharges referred to craniomaxillofacial clinic, Brazil, no age restrictionTBI, facial fractureLow
      McIntyre 2011Retrospective cohortNon = 500, public insurance claims database, Australia, no age restrictionHead injuryVery low
      Moshy 2020Prospective observationalYesn = 132, urban ED, Tanzania, no age restrictionFacial fractureLow
      O'Connor 2002Retrospective cohortYesn = 159, urban autopsies, Australia, no age restrictionTBI, C-spine SCIVery low
      O'Connor 2005Retrospective case-controlYesn = 94, urban SCI unit, Australia, no age restrictionMortality

      C-spine SCI
      Very low
      Porto 2020Prospective observationalYesn = 455, 2 urban trauma centers, Brazil, no age restrictionFacial fractureLow
      Ramli 2014Retrospective case-controlYesn = 755, 4 urban EDs, Malaysia, no age restrictionFacial fractureVery low
      Ramli 2016Cross-sectional surveyYesn = 755, 4 urban EDs, Malaysia, no age restrictionHead injury

      Head injury severity
      Very low
      Rice 2017Retrospective cohortYesn = 7189, state police crash registry, USA, adultsMortality, head injuryLow
      Rocchi 2007Retrospective cohortYesn = 39, urban maxillofacial trauma surgery service, adolescentsFacial fractureVery low
      Sung 2016Retrospective cohortYesn = 738, rural ED, South Korea, adultsHead injury severityLow
      Tripathi 2014Prospective observationalYesn = 1346, urban ED, India, adultsHead injury severityLow
      Tsai 1995Retrospective case-controlYesn = 1351, 16 EDs in variety of population densities, Taiwan, all agesHead injury

      Head injury severity
      Very low
      Usha 2013Before-and-after studyYesn = 191, district maxillofacial trauma service, India, no age restrictionFacial fractureVery low
      Vaughan 1977Retrospective cohortYesn = 1651, urban police crash registry, Australia, all agesFacial fractureVery low
      Wong 2008Retrospective cohortNon = 183, urban hospital trauma registry, Taiwan, all agesH&N, facial injury severityVery low
      Wu 2019Cross-sectional surveyYesn = 405, regional trauma registry patients with head impact, France, adultsHead injury

      Facial injury
      Very low
      Yadukul 2016Retrospective cohortYesn = 220, urban autopsy registry, India, adultsTBI

      Facial fracture
      Very low
      Yeo 1979Retrospective case-controlYesn = 43, urban SCI unit, Australia, no age restrictionC-spine SCIVery low
      Yokoyama 2006Retrospective cohortYesn = 54, urban ED, Japan, no age restrictionH&N, facial injury severityVery low
      Yu 2011Retrospective case-controlYesn = 916, urban ED, Taiwan, no age restrictionTBILow
      ED, emergency department; TBI, traumatic brain injury; C-spine, cervical spine; H&N, head and neck; SCI, spinal cord injury.

      3.2 Mortality

      There were 3 studies reporting on mortality (Table 2).
      • Brewer B.L.
      • Diehl 3rd, A.H.
      • Johnson L.S.
      • et al.
      Choice of motorcycle helmet makes a difference: a prospective observational study.
      ,
      • O'Connor P.J.
      Motorcycle helmets and spinal cord injury: helmet usage and type.
      ,
      • Rice T.M.
      • Troszak L.
      • Erhardt T.
      • et al.
      Novelty helmet use and motorcycle rider fatality.
      All studies were suitable for inclusion in a meta-analysis, which demonstrated no association (OR 0.79 [0.57–1.08]) (Fig. 2A).
      Table 2Summary of evidence.
      Certainty assessment№ of patientsEffectCertaintyImportance
      № of studiesStudy designRisk of biasInconsistencyIndirectnessImprecisionOtherFull-face helmetsNon-full face helmetsRelative (95% CI)Absolute (95% CI)
      Mortality
      3observationalseriousaseriousbnot seriousseriouscnone131/5084 (2.6%)57/1746 (3.3%)OR 0.79 (0.57–1.08)7 fewer per 1000 (from 14 fewer to 3 more)⨁◯◯◯ Very lowCritical
      Injury severity of head and neck, Abbreviated Injury Scale (Scale from: 0 to 6)
      9observationalseriousanot seriousnot seriousseriouscnone54352MD 0.64 lower (1.1 lower to 0.18 lower)⨁◯◯◯ Very lowCritical
      Injury severity of face, Abbreviated Injury Scale (Scale from: 0 to 6)
      7observationalseriousanot seriousnot seriousseriouscnone34336MD 0.49 lower (0.71 lower to 0.27 lower)⨁◯◯◯ Very lowCritical
      Traumatic brain injury
      15observationalseriousanot seriousnot seriousnot seriouslarge effect104/278 (37.4%)165/326 (50.6%)OR 0.40 (0.23–0.70)215 fewer per 1000 (from 315 fewer to 88 fewer)⨁⨁◯◯ LowCritical
      Cervical spinal cord injury
      4observationalseriousaseriousbseriousdseriouscnone55/218 (25.2%)20/38 (52.6%)OR 0.41 (0.09–1.97)213 fewer per 1000 (from 435 fewer to 160 more)⨁◯◯◯ Very lowCritical
      Cervical spine fractures
      5observationalseriousaseriousbnot seriousvery seriouscnone14/101 (13.9%)11/86 (12.8%)OR 1.43 (0.27–7.63)45 more per 1000 (from 90 fewer to 400 more)⨁◯◯◯ Very lowCritical
      Facial fracture
      14observationalseriousanot seriousnot seriousnot seriouslarge effect85/176 (48.3%)74/126 (58.7%)OR 0.26 (0.13–0.50)317 fewer per 1000 (from 431 fewer to 172 fewer)⨁⨁◯◯ LowImportant
      a. small, observational studies; b. heterogeneity of treatment effect; c. low event rate with wide confidence intervals; d. indirect population. CI, confidence interval; MD, mean difference; OR, odds ratio.

      3.3 Injury severity

      There were 12 studies reporting on head, neck, or face injury severity (Table 2).
      • Cannell H.
      • King J.B.
      • Winch R.D.
      Head and facial injuries after low-speed motor-cycle accidents.
      ,
      • Cini M.A.
      • Prado B.G.
      • Hinnig Pde F.
      • et al.
      Influence of type of helmet on facial trauma in motorcycle accidents.
      ,
      • Hitosugi M.
      • Shigeta A.
      • Takatsu A.
      • et al.
      Analysis of fatal injuries to motorcyclists by helmet type.
      ,
      • Liu C.H.
      104 the injury severity of the face, head and neck of motorcyclists in different types of helmets during motor vehicle accidents.
      ,
      • Ramli R.
      • Oxley J.
      Motorcycle helmet fixation status is more crucial than helmet type in providing protection to the head.
      ,
      • Sung K.M.
      • Noble J.
      • Kim S.C.
      • et al.
      The preventive effect of head injury by helmet type in motorcycle crashes: a rural Korean single-center observational study.
      • Tripathi M.
      • Tewari M.K.
      • Mukherjee K.K.
      • Mathuriya S.N.
      Profile of patients with head injury among vehicular accidents: an experience from a tertiary care centre of India.
      • Tsai Y.J.
      • Wang J.D.
      • Huang W.F.
      Case-control study of the effectiveness of different types of helmets for the prevention of head injuries among motorcycle riders in Taipei, Taiwan.
      ,
      • Wong S.L.
      • Liu C.H.
      • Huang Y.C.
      Assessing the facial, head and neck injuries of motorcyclists in various types of helmets during motor vehicle crashes using the abbreviated injury scale.
      ,
      • Yokoyama T.
      • Kawamata H.
      • Hitosugi M.
      • et al.
      Relationship between the severity of oral and maxillofacial injuries and helmet use by type in motorcycle accidents.
      ,
      • Abhinandan Patel K.N.
      • Sneha T.R.
      • Reddy K.R.
      • et al.
      Changing trends in the pattern of maxillofacial injuries in helmeted motorcycle accident patients when compared to non-helmeted motorcycle accident patients.
      ,
      • Colangeli W.
      • Cordaro R.
      • Boschetti C.E.
      • et al.
      Protective effects of helmet type on facial injuries.
      Five studies reported head and neck AIS and were suitable for meta-analysis, which found an association (AIS mean difference −0.64 [−1.10 to −0.18]) with moderate to substantial heterogeneity (I2 = 65%) (Fig. 2B).
      • Cannell H.
      • King J.B.
      • Winch R.D.
      Head and facial injuries after low-speed motor-cycle accidents.
      ,
      • Hitosugi M.
      • Shigeta A.
      • Takatsu A.
      • et al.
      Analysis of fatal injuries to motorcyclists by helmet type.
      ,
      • Liu C.H.
      104 the injury severity of the face, head and neck of motorcyclists in different types of helmets during motor vehicle accidents.
      ,
      • Wong S.L.
      • Liu C.H.
      • Huang Y.C.
      Assessing the facial, head and neck injuries of motorcyclists in various types of helmets during motor vehicle crashes using the abbreviated injury scale.
      ,
      • Yokoyama T.
      • Kawamata H.
      • Hitosugi M.
      • et al.
      Relationship between the severity of oral and maxillofacial injuries and helmet use by type in motorcycle accidents.
      A sensitivity analysis excluding Cannell et al. demonstrated a similar association, (AIS mean difference OR -0.84 [−1.16 to −0.52]) with reduced heterogeneity (I2 = 30%). Four studies reported face AIS and were suitable for meta-analysis, which found an association (AIS mean difference −0.49 [−0.71 to −0.27]) (Fig. 2C).
      • Cannell H.
      • King J.B.
      • Winch R.D.
      Head and facial injuries after low-speed motor-cycle accidents.
      ,
      • Liu C.H.
      104 the injury severity of the face, head and neck of motorcyclists in different types of helmets during motor vehicle accidents.
      ,
      • Wong S.L.
      • Liu C.H.
      • Huang Y.C.
      Assessing the facial, head and neck injuries of motorcyclists in various types of helmets during motor vehicle crashes using the abbreviated injury scale.
      ,
      • Yokoyama T.
      • Kawamata H.
      • Hitosugi M.
      • et al.
      Relationship between the severity of oral and maxillofacial injuries and helmet use by type in motorcycle accidents.
      Among studies reporting on the above outcomes but unable to be included in the meta-analyses, three studies found an association between full-face helmets and reduced injury severity. Abhinandan Patel et al. (n = 741) found that subjects wearing full-face helmets had lower Facial Injury Severity Scores (FISS) (2.0 ± 1.4 vs 3.9 ± 2.3, p < 0.0001) as did Colangeli et al. (n = 287) (2.2 ± 1.5 vs 3.1 ± 2.0, p = 0.0002).
      • Abhinandan Patel K.N.
      • Sneha T.R.
      • Reddy K.R.
      • et al.
      Changing trends in the pattern of maxillofacial injuries in helmeted motorcycle accident patients when compared to non-helmeted motorcycle accident patients.
      ,
      • Colangeli W.
      • Cordaro R.
      • Boschetti C.E.
      • et al.
      Protective effects of helmet type on facial injuries.
      Two studies used AIS to report reductions in injury severity. Sung et al. (n = 738) found the strongest association between full-face helmets and reduced head AIS (full-face −0.4 [−0.6 to −0.2], open-face −0.2 [−0.5 to −0.01], half helmet −0.2 [−0.4 – 0.0]).
      • Sung K.M.
      • Noble J.
      • Kim S.C.
      • et al.
      The preventive effect of head injury by helmet type in motorcycle crashes: a rural Korean single-center observational study.
      Ramli et al. (n = 755) reported that full-face helmets were associated with a lower incidence of severe head injury, defined as AIS 3–6 (0 vs 30%, p = 0.005).
      • Ramli R.
      • Oxley J.
      • Hillard P.
      • et al.
      The effect of motorcycle helmet type, components and fixation status on facial injury in Klang Valley, Malaysia: a case control study.
      Two studies used surrogate outcomes to suggest reductions in injury severity. Cini et al. (n = 157) found that non-full face helmets was associated with an increased risk of operation (OR 3.05 [1.24–7.48]) and Tripathi et al. (n = 1346) found a decreased incidence of moderate to severe TBI in their full-face helmet group (11 vs 37%, p < 0.0001).
      • Cini M.A.
      • Prado B.G.
      • Hinnig Pde F.
      • et al.
      Influence of type of helmet on facial trauma in motorcycle accidents.
      ,
      • Tripathi M.
      • Tewari M.K.
      • Mukherjee K.K.
      • Mathuriya S.N.
      Profile of patients with head injury among vehicular accidents: an experience from a tertiary care centre of India.
      Finally, Tsai et al. (n = 1351) was the sole study to find no difference in moderate to severe TBI incidence between full-face helmets and those that were not (14 vs 19%, p = 1.000).
      • Tsai Y.J.
      • Wang J.D.
      • Huang W.F.
      Case-control study of the effectiveness of different types of helmets for the prevention of head injuries among motorcycle riders in Taipei, Taiwan.

      3.4 Traumatic brain injury

      There were 15 studies reporting on TBI (Table 2).
      • Brewer B.L.
      • Diehl 3rd, A.H.
      • Johnson L.S.
      • et al.
      Choice of motorcycle helmet makes a difference: a prospective observational study.
      ,
      • Capewell S.
      • Reece V.A.
      • Milne D.D.
      Motorcyclists should be encouraged to wear full face crash helmets.
      ,
      • Chiu W.T.
      • Kuo C.Y.
      • Hung C.C.
      • Chen M.
      The effect of the Taiwan motorcycle helmet use law on head injuries.
      ,
      • Erhardt T.
      • Rice T.
      • Troszak L.
      • Zhu M.
      Motorcycle helmet type and the risk of head injury and neck injury during motorcycle collisions in California.
      ,
      • Lam C.
      • Wiratama B.S.
      • Chang W.H.
      • et al.
      Effect of motorcycle helmet types on head injuries: evidence from eight level-I trauma centres in Taiwan.
      ,
      • Liu C.H.
      • Huang Y.C.
      319: the relationship between facial bone fractures with accompanied injuries and the helmet types of the motorcyclists in traffic accidents.
      • Lopes Albuquerque C.E.
      • Nogueira Arcanjo F.P.
      • Cristino-Filho G.
      • et al.
      How safe is your motorcycle helmet?.
      • McIntyre A.
      • Nieuwesteeg M.
      • Cockfield S.
      Motorcyclist Injuries and Protective Clothing: Research with TAC Clients.
      ,
      • O'Connor P.J.
      • Kloeden C.
      • McLean A.J.
      Do full-face helmets offer greater protection against cervical spinal cord injury than open-face helmets?.
      ,
      • Ramli R.
      • Oxley J.
      Motorcycle helmet fixation status is more crucial than helmet type in providing protection to the head.
      ,
      • Rice T.M.
      • Troszak L.
      • Erhardt T.
      • et al.
      Novelty helmet use and motorcycle rider fatality.
      ,
      • Tsai Y.J.
      • Wang J.D.
      • Huang W.F.
      Case-control study of the effectiveness of different types of helmets for the prevention of head injuries among motorcycle riders in Taipei, Taiwan.
      ,
      • Wu D.
      • Dufournet M.
      • Martin J.L.
      Does a full-face helmet effectively protect against facial injuries?.
      ,
      • Yadukul S.
      • Devadass P.K.
      • Gururaj G.
      Role of helmet in preventing head injury among two wheeler occupants in fatal road traffic injuries.
      ,
      • Yu W.Y.
      • Chen C.Y.
      • Chiu W.T.
      • Lin M.R.
      Effectiveness of different types of motorcycle helmets and effects of their improper use on head injuries.
      Four studies were suitable for meta-analysis, which demonstrated a large effect (OR 0.40 [0.23 to 0.70]) (Fig. 2D).
      • Brewer B.L.
      • Diehl 3rd, A.H.
      • Johnson L.S.
      • et al.
      Choice of motorcycle helmet makes a difference: a prospective observational study.
      ,
      • Liu C.H.
      • Huang Y.C.
      319: the relationship between facial bone fractures with accompanied injuries and the helmet types of the motorcyclists in traffic accidents.
      ,
      • Lopes Albuquerque C.E.
      • Nogueira Arcanjo F.P.
      • Cristino-Filho G.
      • et al.
      How safe is your motorcycle helmet?.
      ,
      • O'Connor P.J.
      • Kloeden C.
      • McLean A.J.
      Do full-face helmets offer greater protection against cervical spinal cord injury than open-face helmets?.
      The studies not suitable for data extraction because they did not stratify brain and non-brain head injuries reported similar results, with only 2 of 9 finding no association and none finding a positive association. Capewell et al. (n = 194) found a lower incidence of head and neck injuries comparing full-to open-face helmets (7 vs 34%, p < 0.0001).
      • Capewell S.
      • Reece V.A.
      • Milne D.D.
      Motorcyclists should be encouraged to wear full face crash helmets.
      Chiu et al. (n = 8795) reported an association between non-full face helmets and severe head injury, defined as Glasgow Coma Scale (GCS) ≤8 (OR 1.76 [1.15–2.69]).
      • Chiu W.T.
      • Kuo C.Y.
      • Hung C.C.
      • Chen M.
      The effect of the Taiwan motorcycle helmet use law on head injuries.
      Erhardt et al. (n = 7545) and Rice et al. (n = 7189) found that full-face helmets had a lower incidence of head injury (11 vs 23%, p < 0.0001) and (11 vs 30%, p < 0.0001), respectively, while McIntyre et al. (n = 500) reported similar findings for open head injuries (3 vs 14%, p < 0.001).
      • Erhardt T.
      • Rice T.
      • Troszak L.
      • Zhu M.
      Motorcycle helmet type and the risk of head injury and neck injury during motorcycle collisions in California.
      ,
      • McIntyre A.
      • Nieuwesteeg M.
      • Cockfield S.
      Motorcyclist Injuries and Protective Clothing: Research with TAC Clients.
      ,
      • Rice T.M.
      • Troszak L.
      • Erhardt T.
      • et al.
      Novelty helmet use and motorcycle rider fatality.
      While Lam et al. (n = 725) reported an association between non-full face helmets and head injury (OR 1.32 [1.07–1.63]), Ramli et al. (n = 755) and Wu et al. (n = 405) found no association between non-full face helmets and head injury (OR 1.86 [0.57–6.09]) and non-facial head injury (OR 0.84 [0.33–2.13]), respectively.
      • Lam C.
      • Wiratama B.S.
      • Chang W.H.
      • et al.
      Effect of motorcycle helmet types on head injuries: evidence from eight level-I trauma centres in Taiwan.
      ,
      • Ramli R.
      • Oxley J.
      Motorcycle helmet fixation status is more crucial than helmet type in providing protection to the head.
      ,
      • Wu D.
      • Dufournet M.
      • Martin J.L.
      Does a full-face helmet effectively protect against facial injuries?.
      Tsai et al. (n = 1351) indirectly suggested a difference by reporting that compared to unhelmeted subjects, those wearing full-face helmets had a lower risk of head injury (OR 0.26 [0.14–0.47]) while those wearing non-full face helmets did not (OR 0.72 [0.38–1.37]).
      • Tsai Y.J.
      • Wang J.D.
      • Huang W.F.
      Case-control study of the effectiveness of different types of helmets for the prevention of head injuries among motorcycle riders in Taipei, Taiwan.
      Yadukul et al. (n = 220) found that full-face helmets reduced incidence of TBI (21% vs 90%, p = 0.0158) but no helmets met national quality standards.
      • Yadukul S.
      • Devadass P.K.
      • Gururaj G.
      Role of helmet in preventing head injury among two wheeler occupants in fatal road traffic injuries.
      Yu et al. (n = 916) compared full-face helmets to open-face and half helmets separately. Relative to full-face helmets, there was an association with half-helmets (OR 2.10 [1.01–4.38]) but not open-face helmets (OR 1.03 [0.44–2.43]).
      • Yu W.Y.
      • Chen C.Y.
      • Chiu W.T.
      • Lin M.R.
      Effectiveness of different types of motorcycle helmets and effects of their improper use on head injuries.

      3.5 Cervical spinal cord injury

      There were 4 studies reporting on cervical SCI (Table 2).
      • Lin M.R.
      • Tsauo J.Y.
      • Hwang H.F.
      • et al.
      Relation between motorcycle helmet use and cervical spinal cord injury.
      ,
      • O'Connor P.J.
      Motorcycle helmets and spinal cord injury: helmet usage and type.
      ,
      • O'Connor P.J.
      • Kloeden C.
      • McLean A.J.
      Do full-face helmets offer greater protection against cervical spinal cord injury than open-face helmets?.
      ,
      • Yeo J.D.
      Five-year review of spinal cord injuries in motorcyclists.
      Three studies were suitable for meta-analysis, which demonstrated no association (OR 0.41 [0.09–1.97]) though with moderate to substantial heterogeneity (I2 = 64%) (Fig. 2E).
      • O'Connor P.J.
      Motorcycle helmets and spinal cord injury: helmet usage and type.
      ,
      • O'Connor P.J.
      • Kloeden C.
      • McLean A.J.
      Do full-face helmets offer greater protection against cervical spinal cord injury than open-face helmets?.
      ,
      • Yeo J.D.
      Five-year review of spinal cord injuries in motorcyclists.
      A sensitivity analysis excluding Yeo et al. still showed no association (OR 0.86 [0.33–2.27]), but with less heterogeneity (I2 = 0). Lin et al. (n = 147), thoughnot suitable for data extraction, indirectly reported no association: compared to unhelmeted subjects neither full-face helmets (OR 0.57 [0.06–5.50]) nor non-full face helmets (OR 0.52 [0.10–2.65]) were associated with cervical SCI.
      • Lin M.R.
      • Tsauo J.Y.
      • Hwang H.F.
      • et al.
      Relation between motorcycle helmet use and cervical spinal cord injury.

      3.6 Cervical spine fracture

      There were 5 studies reporting on cervical spine fracture (Table 2).
      • Brewer B.L.
      • Diehl 3rd, A.H.
      • Johnson L.S.
      • et al.
      Choice of motorcycle helmet makes a difference: a prospective observational study.
      ,
      • Capewell S.
      • Reece V.A.
      • Milne D.D.
      Motorcyclists should be encouraged to wear full face crash helmets.
      ,
      • Erhardt T.
      • Rice T.
      • Troszak L.
      • Zhu M.
      Motorcycle helmet type and the risk of head injury and neck injury during motorcycle collisions in California.
      • Hitosugi M.
      • Shigeta A.
      • Takatsu A.
      • et al.
      Analysis of fatal injuries to motorcyclists by helmet type.
      • Lam C.
      • Wiratama B.S.
      • Chang W.H.
      • et al.
      Effect of motorcycle helmet types on head injuries: evidence from eight level-I trauma centres in Taiwan.
      Two studies were suitable for meta-analysis, demonstrating no association (OR 1.43 [0.27–7.63]) though with moderate to substantial heterogeneity (I2 = 68%) (Fig. 2F).
      • Brewer B.L.
      • Diehl 3rd, A.H.
      • Johnson L.S.
      • et al.
      Choice of motorcycle helmet makes a difference: a prospective observational study.
      ,
      • Hitosugi M.
      • Shigeta A.
      • Takatsu A.
      • et al.
      Analysis of fatal injuries to motorcyclists by helmet type.
      The studies not suitable for data extraction because they did not stratify cervical spine fractures reported mostly similar results, with 2 of 3 finding an association, but most likely due to head injuries rather than neck injuries. Capewell et al. combined head and neck injuries and found a lower incidence among full-face helmeted riders as reported above.
      • Capewell S.
      • Reece V.A.
      • Milne D.D.
      Motorcyclists should be encouraged to wear full face crash helmets.
      Erhardt et al. found no difference in incidence of neck injuries among subjects with and without full-face helmets (8% vs 9%, p = 0.4184).
      • Erhardt T.
      • Rice T.
      • Troszak L.
      • Zhu M.
      Motorcycle helmet type and the risk of head injury and neck injury during motorcycle collisions in California.
      Lam et al. (n = 725) combined head and neck injuries and reported that non-full face helmets increased injury incidence (OR 1.32 [1.07–1.63]).
      • Lam C.
      • Wiratama B.S.
      • Chang W.H.
      • et al.
      Effect of motorcycle helmet types on head injuries: evidence from eight level-I trauma centres in Taiwan.

      3.7 Blunt cerebrovascular injury

      There were no studies that reported on blunt cerebrovascular injury.

      3.8 Facial fracture

      There were 14 studies reporting on facial fracture (Table 2).
      • Arif M.Z.
      • B R.R.
      • Prasad K.
      The role of helmet fastening in motorcycle road traffic accidents.
      ,
      • Brewer B.L.
      • Diehl 3rd, A.H.
      • Johnson L.S.
      • et al.
      Choice of motorcycle helmet makes a difference: a prospective observational study.
      ,
      • Cavalcante J.R.
      • Oka S.C.
      • de Santana Santos T.
      • et al.
      Influence of helmet use in facial trauma and moderate traumatic brain injury victims of motorcycle accidents.
      ,
      • Liu C.H.
      • Huang Y.C.
      319: the relationship between facial bone fractures with accompanied injuries and the helmet types of the motorcyclists in traffic accidents.
      ,
      • Lopes Albuquerque C.E.
      • Nogueira Arcanjo F.P.
      • Cristino-Filho G.
      • et al.
      How safe is your motorcycle helmet?.
      ,
      • Moshy J.R.
      • Msemakweli B.S.
      • Owibingire S.S.
      • Sohal K.S.
      Pattern of mandibular fractures and helmet use among motorcycle crash victims in Tanzania.
      ,
      • Porto G.G.
      • de Menezes L.P.
      • Cavalcante D.K.F.
      • et al.
      Do type of helmet and alcohol use increase facial trauma severity?.
      ,
      • Ramli R.
      • Oxley J.
      • Hillard P.
      • et al.
      The effect of motorcycle helmet type, components and fixation status on facial injury in Klang Valley, Malaysia: a case control study.
      ,
      • Vaughan R.G.
      Motor cycle helmets and facial injuries.
      ,
      • Yadukul S.
      • Devadass P.K.
      • Gururaj G.
      Role of helmet in preventing head injury among two wheeler occupants in fatal road traffic injuries.
      ,
      • Abhinandan Patel K.N.
      • Sneha T.R.
      • Reddy K.R.
      • et al.
      Changing trends in the pattern of maxillofacial injuries in helmeted motorcycle accident patients when compared to non-helmeted motorcycle accident patients.
      ,
      • Brasileiro B.F.
      • Vieira J.M.
      • da Silveira C.E.S.
      Avaliação de traumatismos faciais por acidentes motociclísticos em Aracaju/SE.
      • Rocchi G.
      • Fadda M.T.
      • Marianetti T.M.
      • et al.
      Craniofacial trauma in adolescents: incidence, etiology, and prevention.
      • Usha M.
      • Ravindran V.
      • Soumithran C.S.
      • Ravindran Nair K.S.
      The impact of mandatory helmet law on the outcome of maxillo facial trauma: a comparative study in Kerala.
      Nine studies were suitable for meta-analysis, which found a large effect (OR 0.26 [0.15–0.46]) (Fig. 2G).
      • Arif M.Z.
      • B R.R.
      • Prasad K.
      The role of helmet fastening in motorcycle road traffic accidents.
      ,
      • Brewer B.L.
      • Diehl 3rd, A.H.
      • Johnson L.S.
      • et al.
      Choice of motorcycle helmet makes a difference: a prospective observational study.
      ,
      • Cavalcante J.R.
      • Oka S.C.
      • de Santana Santos T.
      • et al.
      Influence of helmet use in facial trauma and moderate traumatic brain injury victims of motorcycle accidents.
      ,
      • Liu C.H.
      • Huang Y.C.
      319: the relationship between facial bone fractures with accompanied injuries and the helmet types of the motorcyclists in traffic accidents.
      ,
      • Lopes Albuquerque C.E.
      • Nogueira Arcanjo F.P.
      • Cristino-Filho G.
      • et al.
      How safe is your motorcycle helmet?.
      ,
      • Moshy J.R.
      • Msemakweli B.S.
      • Owibingire S.S.
      • Sohal K.S.
      Pattern of mandibular fractures and helmet use among motorcycle crash victims in Tanzania.
      ,
      • Vaughan R.G.
      Motor cycle helmets and facial injuries.
      ,
      • Brasileiro B.F.
      • Vieira J.M.
      • da Silveira C.E.S.
      Avaliação de traumatismos faciais por acidentes motociclísticos em Aracaju/SE.
      ,
      • Usha M.
      • Ravindran V.
      • Soumithran C.S.
      • Ravindran Nair K.S.
      The impact of mandatory helmet law on the outcome of maxillo facial trauma: a comparative study in Kerala.
      Among studies reporting on facial fracture but unable to be included in the meta-analyses, Abhinandan Patel et al. (n = 741) reported 103 fractures in 140 full-face helmet subjects and 660 fractures in 364 non-full face helmet subjects.
      • Abhinandan Patel K.N.
      • Sneha T.R.
      • Reddy K.R.
      • et al.
      Changing trends in the pattern of maxillofacial injuries in helmeted motorcycle accident patients when compared to non-helmeted motorcycle accident patients.
      Rocchi et al. (n = 39) reported 3 fractures in 3 adolescents wearing full-face helmets and 37 fractures in 19 adolescents wearing non-full face helmets.
      • Rocchi G.
      • Fadda M.T.
      • Marianetti T.M.
      • et al.
      Craniofacial trauma in adolescents: incidence, etiology, and prevention.
      The remaining three studies did not find any difference. Porto et al. (n = 455) reported no association between the use of non-full face helmets and severe facial injury, defined as FISS ≥6 (OR 1.99 [0.86–4.63]).
      • Porto G.G.
      • de Menezes L.P.
      • Cavalcante D.K.F.
      • et al.
      Do type of helmet and alcohol use increase facial trauma severity?.
      Ramli et al. (n = 755) found no association between open-face and half-helmets (OR 1.43 [0.50–4.04]) or “tropical” helmets (OR 1.47 [0.43–5.10]), which are most similar to half-helmets, and facial injury, though their study was confounded by the facts that 30% of helmets were not fastened and 7% did not meet national quality standards.
      • Ramli R.
      • Oxley J.
      • Hillard P.
      • et al.
      The effect of motorcycle helmet type, components and fixation status on facial injury in Klang Valley, Malaysia: a case control study.
      Yadukul et al. (n = 220) did not report any facial fractures in riders using approved full-face helmets (n = 15), but no non-full face helmets met national standards.
      • Yadukul S.
      • Devadass P.K.
      • Gururaj G.
      Role of helmet in preventing head injury among two wheeler occupants in fatal road traffic injuries.

      4. Discussion

      4.1 Recommendation

      In developing a recommendation, GRADE suggests taking into consideration not only the results but also: the potential harms and benefits, patients values and preferences, and the predicted burden and use of resources to implement the recommendation.
      • Andrews J.C.
      • Schunemann H.J.
      • Oxman A.D.
      • et al.
      GRADE guidelines: 15. Going from evidence to recommendation-determinants of a recommendation's direction and strength.
      Based on these factors, 11 out of 11 authors voted in favor of the following:
      We conditionally recommend that motorcycle riders wear full-face helmets to reduce traumatic brain injury, facial fracture, and head, face, and neck injury severity.
      The overall quality of evidence was graded as very low. All studies were non-randomized with most having risk of bias, inconsistency, and imprecision. On the other hand, 2 of 7 outcomes demonstrated a large effect size of intervention, upgrading their quality of evidence to low. Of note, when upgrading non-randomized studies, there is a risk of magnifying bias, thus overestimating effect.
      • Guyatt G.H.
      • Oxman A.D.
      • Sultan S.
      • et al.
      GRADE guidelines: 9. Rating up the quality of evidence.
      However, that the upper limit of the confidence intervals were not near one and both sets of studies demonstrated consistent results allowed the group to more confidently upgrade the quality of evidence.
      • Higgins J.P.T.
      • Thomas J.
      • Chandler J.
      • et al.
      Cochrane Handbook for Systematic Reviews of Interventions: Cochrane.
      With respect to harms and benefits, based on prior meta-analysis, there appears to be no harm to motorcycle riders who wear full-face helmets.
      • Lucci C.
      • Piantini S.
      • Savino G.
      • Pierini M.
      Motorcycle helmet selection and usage for improved safety: a systematic review on the protective effects of helmet type and fastening.
      On the other hand, increased protection and thus reduced morbidity would seem to benefit both riders and society by reducing overall costs and quality-of-life years lost. Further research is needed.
      With respect to patient values and burden, there is evidence to suggest that rider preferences, though varied by subculture, may be a barrier to implementation.
      • Tsui C.K.
      • Rice T.M.
      • Pande S.
      Predictors of nonstandard helmet use among San Francisco Bay-area motorcyclists.
      Surveys of both drivers and passengers suggest that the cost, discomfort, and perceived reductions in visual and auditory acuity associated with a full-face helmet decrease their desire to wear one.
      • Khan I.
      • Khan A.
      • Aziz F.
      • et al.
      Factors associated with helmet use among motorcycle users in Karachi, Pakistan.
      • Pham K.H.
      • Le Thi Q.X.
      • Petrie D.J.
      • et al.
      Households' willingness to pay for a motorcycle helmet in Hanoi, Vietnam.
      • Ranney M.L.
      • Mello M.J.
      • Baird J.B.
      • et al.
      Correlates of motorcycle helmet use among recent graduates of a motorcycle training course.
      • Akaateba M.A.
      • Yakubu I.
      • Akanbang B.A.
      Correlates and barriers associated with motorcycle helmet use in wa, Ghana.
      • Fong M.C.
      • Measelle J.R.
      • Dwyer J.L.
      • et al.
      Rates of motorcycle helmet use and reasons for non-use among adults and children in Luang Prabang, Lao People's Democratic Republic.
      • Karuppanagounder K.
      • Vijayan A.V.
      Motorcycle helmet use in Calicut, India: user behaviors, attitudes, and perceptions.
      • Bachani A.M.
      • Hung Y.W.
      • Mogere S.
      • et al.
      Helmet wearing in Kenya: prevalence, knowledge, attitude, practice and implications.
      In actuality, full-face helmet use does not functionally impair cognitive performance.
      • McKnight A.J.
      • McKnight A.S.
      The effects of motorcycle helmets upon seeing and hearing.
      ,
      • Bogerd C.P.
      • Walker I.
      • Bruhwiler P.A.
      • Rossi R.M.
      The effect of a helmet on cognitive performance is, at worst, marginal: a controlled laboratory study.
      Discomfort can result from weight, poor fit due to limited availability that does not take into consideration female or child users, or environment, such as overheating due to airflow reduction.
      • Fong M.C.
      • Measelle J.R.
      • Dwyer J.L.
      • et al.
      Rates of motorcycle helmet use and reasons for non-use among adults and children in Luang Prabang, Lao People's Democratic Republic.
      ,
      • Chiou M.
      • Wickremasinghe W.
      • Kache S.
      • Tennakoon L.
      Barriers to using motorcycle helmets among children between 3 and 18 Years old in kurunegala district of Sri Lanka: a descriptive study of use, knowledge, attitudes, and practices.
      ,
      • Siddiqui S.
      • Arora S.
      • Peipert J.
      • et al.
      Survey of helmet influences of female pillions in New Delhi.
      This is particularly relevant in subtropical and tropical climates, where most motorcycle riders reside.
      World Bank Development Indicators
      Time Series: Two-Wheelers (Per 1,000 People).
      Thus, the working group extrapolated that some motorcycle riders are unlikely to choose to wear full-face helmets. Like prior transportation injury prevention initiatives such as seat belt or helmet use, it is likely that enactment and, importantly, enforcement of legislation will be a necessary part of any injury prevention efforts around full-face helmet utilization.
      With respect to resource use, the higher cost of a full-face helmet may be a barrier to a significant number of motorcycle riders, especially in lower- and middle-income countries.
      World Bank Development Indicators
      Time Series: Two-Wheelers (Per 1,000 People).
      Further, given aforementioned rider concerns about full-face helmets, it is likely that the ideal full-face helmet does not yet exist. We call to action stakeholders who research and develop motorcycle helmets to focus their efforts on improving full-face helmets for the over 200 hundred million motorcycle riders worldwide.
      World Bank Development Indicators
      Time Series: Two-Wheelers (Per 1,000 People).

      4.2 Using these guidelines in clinical practice

      Clinicians should encourage the use of full-face helmets while understanding that the role of the clinician in the face of a conditional recommendation should be to help their patient “arrive at a management decision consistent with [patient] values and preferences.”
      • Callcut R.A.
      • Raja A.S.
      • Como J.J.
      • et al.
      Writing an EAST Practice Management Guideline (PMG): A Step-by-step How-To-Guide.

      4.3 Limitations

      There are important limitations to note. First, the systematic review and meta-analyses are limited by the quality of evidence. The increased risk of selection bias found in low quality evidence may have led to confounding, reporting bias, imprecision, and inability to determine causality. Few studies reported on whether helmets fit, were fastened, or met quality standards, which are known confounders.
      • Lucci C.
      • Piantini S.
      • Savino G.
      • Pierini M.
      Motorcycle helmet selection and usage for improved safety: a systematic review on the protective effects of helmet type and fastening.
      A recent international study on helmet standards estimated that up to half of helmets used in low- and middle-income countries may be nonstandard.
      • Road Traffic Injuries Research Network Multicenter Study C.
      • Ackaah W.
      • Afukaar F.
      • et al.
      The use of non-standard motorcycle helmets in low- and middle-income countries: a multicentre study.
      Finally, motorcycle subcultures often have different helmet type preferences, riding styles, and speeds, but were not reported in most studies.
      • Tsui C.K.
      • Rice T.M.
      • Pande S.
      Predictors of nonstandard helmet use among San Francisco Bay-area motorcyclists.
      Second, heterogeneity may limit conclusions. The prespecified assumption, which was confirmed by the literature search, was that there would be a paucity of evidence on this topic and an effort to collect as much data as possible was made. Nearly all heterogeneity appeared to be the result of studies performed in outlying years (1977, 1979, and 1982). Regional differences in helmet standards may have contributed. Further, variations in riding environment or traffic control infrastructure and enforcement may have also played a role. Heterogeneity was explored via random effects modeling and sensitivity analyses, the latter confirming that studies contributing to heterogeneity did not contribute significantly to effect size. Additionally, for outcomes with moderate to substantial heterogeneity, the overall number of studies included was small (range 2–5), which can limit I2 accuracy.
      • von Hippel P.T.
      The heterogeneity statistic I(2) can be biased in small meta-analyses.
      Further, for the most influential outcomes, heterogeneity was <40%, which may not be important.
      • Higgins J.P.T.
      • Thomas J.
      • Chandler J.
      • et al.
      Cochrane Handbook for Systematic Reviews of Interventions: Cochrane.
      Finally, use of dichotomous outcomes may preclude a more nuanced analysis that could be of interest to clinicians and patients. Injury severity and functional outcomes are poorly studied. Reporting of injury severity is also heterogeneous, making comparisons among studies difficult and drawing conclusions even more difficult.

      4.4 Future directions

      Future research should include: cost analyses, quality of life measurements, injury severity metrics, and long-term outcomes. Research would benefit from a prospective study design that captures and adjusts for important confounders such as fastening, fit, motorcycle subculture, and whether the helmet meets quality standards. Each confounder has been previously reported in the literature, suggesting feasibility, but is far from standard. It will also be important to focus on better understanding of and overcoming barriers to wearing a full-face helmet. Integrating electronic technology is a potential area of development.
      • Tabary M.
      • Ahmadi S.
      • Amirzade-Iranaq M.H.
      • et al.
      The effectiveness of different types of motorcycle helmets - a scoping review.
      Improving the quality and breadth of data will allow for better community and legislative education and interventions.

      5. Conclusions

      We conditionally recommend using full-face helmets for motorcycle riders to reduce traumatic brain injury, facial fracture, and injury severity of the head, neck, and face. Stakeholders who research and develop helmets ought to focus on improving full-face helmet design to increase utilization.

      Authorship

      EMU and RR designed the study. EMU, JMR, and RR searched the literature. All authors collected, analyzed, and interpreted the data. EMU, NB, LMK, KHS, JMR, and RR drafted the article. All authors critically revised the article and approved the final version.

      Declaration of competing interest

      ZMB is a paid educational consultant for Zimmer-Biomet and KLS-Martin for areas unrelated to the current study.

      Acknowledgements

      Celine Soudant, MLIS, research librarian at Memorial Sloan Kettering Cancer Center peer-reviewed the search strategy. Caroline Park, MD, MPH, Assistant Professor of Surgery at University of Texas Southwestern; Gayle Minard, MD, retired; Stepheny Berry, MD, Assistant Professor of Surgery at University of Kansas; and, Samuel Cemaj, MD, Associate Professor of Surgery at University of Nebraska, all acute care surgeons who also ride motorcycles, provided supplemental opinion on patient values and preferences.

      Appendix A. Supplementary data

      The following are the Supplementary data to this article:

      References

        • Liu B.C.
        • Ivers R.
        • Norton R.
        • et al.
        Helmets for preventing injury in motorcycle riders.
        Cochrane Database Syst Rev. 2008; 1: CD004333
        • WHO
        Global Status Report on Road Safety 2018.
        World Health Organization, Geneva, Switzerland2018
        • MacLeod J.B.
        • Digiacomo J.C.
        • Tinkoff G.
        An evidence-based review: helmet efficacy to reduce head injury and mortality in motorcycle crashes: EAST practice management guidelines.
        J Trauma. 2010; 69: 1101-1111
        • Tabary M.
        • Ahmadi S.
        • Amirzade-Iranaq M.H.
        • et al.
        The effectiveness of different types of motorcycle helmets - a scoping review.
        Accid Anal Prev. 2021; 154106065
        • Lucci C.
        • Piantini S.
        • Savino G.
        • Pierini M.
        Motorcycle helmet selection and usage for improved safety: a systematic review on the protective effects of helmet type and fastening.
        Traffic Inj Prev. 2021; 22: 301-306
        • Chaichan S.
        • Asawalertsaeng T.
        • Veerapongtongchai P.
        • et al.
        Are full-face helmets the most effective in preventing head and neck injury in motorcycle accidents? A meta-analysis.
        Prev Med Rep. 2020; 19101118
        • Higgins J.P.T.
        • Thomas J.
        • Chandler J.
        • et al.
        Cochrane Handbook for Systematic Reviews of Interventions: Cochrane.
        2021 ([updated February 2021October 29, 2021]. Available from:)
        • Cavalcante D.K.F.
        • Veloso S.R.M.
        • Durao M.A.
        • et al.
        Do helmet use and type influence facial trauma occurrence and severity in motorcyclists? A systematic review and meta-analysis.
        J Oral Maxillofac Surg. 2021; 79: 1492-1506
        • Guyatt G.H.
        • Oxman A.D.
        • Vist G.E.
        • et al.
        GRADE: an emerging consensus on rating quality of evidence and strength of recommendations.
        BMJ. 2008; 336: 924-926
        • Kerwin A.J.
        • Haut E.R.
        • Burns J.B.
        • et al.
        The eastern association of the Surgery of trauma approach to practice management guideline development using grading of recommendations, assessment, development, and evaluation (GRADE) methodology.
        J Trauma Acute Care Surg. 2012; 73: S283-S287
        • Higgins J.P.T.
        • Lasserson T.
        • Chandler J.
        • et al.
        Methodological Expectations of Cochrane Intervention Reviews.
        Cochrane, London2021
        • Clark J.M.
        • Sanders S.
        • Carter M.
        • et al.
        Improving the translation of search strategies using the Polyglot Search Translator: a randomized controlled trial.
        J Med Libr Assoc. 2020; 108: 195-207
        • Rethlefsen M.L.
        • Kirtley S.
        • Waffenschmidt S.
        • et al.
        PRISMA-S: an extension to the PRISMA statement for reporting literature searches in systematic reviews.
        Syst Rev. 2021; 10: 39
        • McGowan J.
        • Sampson M.
        • Salzwedel D.M.
        • et al.
        PRESS peer review of electronic search strategies: 2015 guideline statement.
        J Clin Epidemiol. 2016; 75: 40-46
        • Page M.J.
        • McKenzie J.E.
        • Bossuyt P.M.
        • et al.
        The PRISMA 2020 statement: an updated guideline for reporting systematic reviews.
        Int J Surg. 2021; 88105906
      1. Oransky I, Marcus A. Retraction Watch [updated November 2021November 2, 2021]. Available from: https://retractionwatch.com.

        • Arif M.Z.
        • B R.R.
        • Prasad K.
        The role of helmet fastening in motorcycle road traffic accidents.
        Craniomaxillofacial Trauma Reconstr. 2019; 12: 284-290
        • Brewer B.L.
        • Diehl 3rd, A.H.
        • Johnson L.S.
        • et al.
        Choice of motorcycle helmet makes a difference: a prospective observational study.
        J Trauma Acute Care Surg. 2013; 75: 88-91
        • Cannell H.
        • King J.B.
        • Winch R.D.
        Head and facial injuries after low-speed motor-cycle accidents.
        Br J Oral Surg. 1982; 20: 183-191
        • Capewell S.
        • Reece V.A.
        • Milne D.D.
        Motorcyclists should be encouraged to wear full face crash helmets.
        Br Med J. 1984; 288: 1230-1231
        • Cavalcante J.R.
        • Oka S.C.
        • de Santana Santos T.
        • et al.
        Influence of helmet use in facial trauma and moderate traumatic brain injury victims of motorcycle accidents.
        J Craniofac Surg. 2012; 23: 982-985
        • Chiu W.T.
        • Kuo C.Y.
        • Hung C.C.
        • Chen M.
        The effect of the Taiwan motorcycle helmet use law on head injuries.
        Am J Publ Health. 2000; 90: 793-796
        • Cini M.A.
        • Prado B.G.
        • Hinnig Pde F.
        • et al.
        Influence of type of helmet on facial trauma in motorcycle accidents.
        Br J Oral Maxillofac Surg. 2014; 52: 789-792
        • Erhardt T.
        • Rice T.
        • Troszak L.
        • Zhu M.
        Motorcycle helmet type and the risk of head injury and neck injury during motorcycle collisions in California.
        Accid Anal Prev. 2016; 86: 23-28
        • Hitosugi M.
        • Shigeta A.
        • Takatsu A.
        • et al.
        Analysis of fatal injuries to motorcyclists by helmet type.
        Am J Forensic Med Pathol. 2004; 25: 125-128
        • Lam C.
        • Wiratama B.S.
        • Chang W.H.
        • et al.
        Effect of motorcycle helmet types on head injuries: evidence from eight level-I trauma centres in Taiwan.
        BMC Publ Health. 2020; 20: 78
        • Lin M.R.
        • Tsauo J.Y.
        • Hwang H.F.
        • et al.
        Relation between motorcycle helmet use and cervical spinal cord injury.
        Neuroepidemiology. 2004; 23: 269-274
        • Liu C.H.
        104 the injury severity of the face, head and neck of motorcyclists in different types of helmets during motor vehicle accidents.
        Ann Emerg Med. 2012; 60: S38
        • Liu C.H.
        • Huang Y.C.
        319: the relationship between facial bone fractures with accompanied injuries and the helmet types of the motorcyclists in traffic accidents.
        Ann Emerg Med. 2007; 50 (S100-S)
        • Lopes Albuquerque C.E.
        • Nogueira Arcanjo F.P.
        • Cristino-Filho G.
        • et al.
        How safe is your motorcycle helmet?.
        J Oral Maxillofac Surg. 2014; 72: 542-549
        • McIntyre A.
        • Nieuwesteeg M.
        • Cockfield S.
        Motorcyclist Injuries and Protective Clothing: Research with TAC Clients.
        Transport Accident Commission of Victoria, Melbourne, Australia2011
        • Moshy J.R.
        • Msemakweli B.S.
        • Owibingire S.S.
        • Sohal K.S.
        Pattern of mandibular fractures and helmet use among motorcycle crash victims in Tanzania.
        Afr Health Sci. 2020; 20: 789-797
        • O'Connor P.J.
        Motorcycle helmets and spinal cord injury: helmet usage and type.
        Traffic Inj Prev. 2005; 6: 60-66
        • O'Connor P.J.
        • Kloeden C.
        • McLean A.J.
        Do full-face helmets offer greater protection against cervical spinal cord injury than open-face helmets?.
        Traffic Inj Prev. 2002; 3: 247-250
        • Porto G.G.
        • de Menezes L.P.
        • Cavalcante D.K.F.
        • et al.
        Do type of helmet and alcohol use increase facial trauma severity?.
        J Oral Maxillofac Surg. 2020; 78: 797 e1-e8
        • Ramli R.
        • Oxley J.
        Motorcycle helmet fixation status is more crucial than helmet type in providing protection to the head.
        Injury. 2016; 47: 2442-2449
        • Ramli R.
        • Oxley J.
        • Hillard P.
        • et al.
        The effect of motorcycle helmet type, components and fixation status on facial injury in Klang Valley, Malaysia: a case control study.
        BMC Emerg Med. 2014; 14: 17
        • Rice T.M.
        • Troszak L.
        • Erhardt T.
        • et al.
        Novelty helmet use and motorcycle rider fatality.
        Accid Anal Prev. 2017; 103: 123-128
        • Sung K.M.
        • Noble J.
        • Kim S.C.
        • et al.
        The preventive effect of head injury by helmet type in motorcycle crashes: a rural Korean single-center observational study.
        BioMed Res Int. 2016; (2016)1849134
        • Tripathi M.
        • Tewari M.K.
        • Mukherjee K.K.
        • Mathuriya S.N.
        Profile of patients with head injury among vehicular accidents: an experience from a tertiary care centre of India.
        Neurol India. 2014; 62: 610-617
        • Tsai Y.J.
        • Wang J.D.
        • Huang W.F.
        Case-control study of the effectiveness of different types of helmets for the prevention of head injuries among motorcycle riders in Taipei, Taiwan.
        Am J Epidemiol. 1995; 142: 974‐81
        • Vaughan R.G.
        Motor cycle helmets and facial injuries.
        Med J Aust. 1977; 1: 125-127
        • Wong S.L.
        • Liu C.H.
        • Huang Y.C.
        Assessing the facial, head and neck injuries of motorcyclists in various types of helmets during motor vehicle crashes using the abbreviated injury scale.
        Ann Emerg Med. 2008; 52
        • Wu D.
        • Dufournet M.
        • Martin J.L.
        Does a full-face helmet effectively protect against facial injuries?.
        Inj Epidemiol. 2019; 6: 19
        • Yadukul S.
        • Devadass P.K.
        • Gururaj G.
        Role of helmet in preventing head injury among two wheeler occupants in fatal road traffic injuries.
        Indian J Forensic Med Toxicol. 2016; 10: 6-10
        • Yeo J.D.
        Five-year review of spinal cord injuries in motorcyclists.
        Med J Aust. 1979; 2: 381
        • Yokoyama T.
        • Kawamata H.
        • Hitosugi M.
        • et al.
        Relationship between the severity of oral and maxillofacial injuries and helmet use by type in motorcycle accidents.
        Dokkyo J Med Sci. 2006; 33: 11-16
        • Yu W.Y.
        • Chen C.Y.
        • Chiu W.T.
        • Lin M.R.
        Effectiveness of different types of motorcycle helmets and effects of their improper use on head injuries.
        Int J Epidemiol. 2011; 40: 794-803
        • Abhinandan Patel K.N.
        • Sneha T.R.
        • Reddy K.R.
        • et al.
        Changing trends in the pattern of maxillofacial injuries in helmeted motorcycle accident patients when compared to non-helmeted motorcycle accident patients.
        J Maxillofac Oral Surg. 2021;
        • Colangeli W.
        • Cordaro R.
        • Boschetti C.E.
        • et al.
        Protective effects of helmet type on facial injuries.
        J Craniofac Surg. 2021; 32: 1591-1595
        • Brasileiro B.F.
        • Vieira J.M.
        • da Silveira C.E.S.
        Avaliação de traumatismos faciais por acidentes motociclísticos em Aracaju/SE.
        Rev Cir Traumatol Buco-Maxilo-fac. 2010; 10: 97-104
        • Rocchi G.
        • Fadda M.T.
        • Marianetti T.M.
        • et al.
        Craniofacial trauma in adolescents: incidence, etiology, and prevention.
        J Trauma. 2007; 62: 404-409
        • Usha M.
        • Ravindran V.
        • Soumithran C.S.
        • Ravindran Nair K.S.
        The impact of mandatory helmet law on the outcome of maxillo facial trauma: a comparative study in Kerala.
        J Maxillofac Oral Surg. 2014; 13: 176-183
        • Amirjamshidi A.
        • Ardalan A.
        • Nainei K.H.
        • et al.
        Comparison of standard and nonstandard helmets and variants influencing the choice of helmets: a preliminary report of cross-sectional prospective analysis of 100 cases.
        Surg Neurol Int. 2011; 2: 49
        • Arif M.Z.
        • Rajanikanth B.R.
        • Prasad K.
        Soft tissue injuries of the maxillofacial region occurring from motorcycle accidents.
        J Maxillofac Oral Surg. 2019; 18: 432-439
        • Andrews J.C.
        • Schunemann H.J.
        • Oxman A.D.
        • et al.
        GRADE guidelines: 15. Going from evidence to recommendation-determinants of a recommendation's direction and strength.
        J Clin Epidemiol. 2013; 66: 726-735
        • Guyatt G.H.
        • Oxman A.D.
        • Sultan S.
        • et al.
        GRADE guidelines: 9. Rating up the quality of evidence.
        J Clin Epidemiol. 2011; 64: 1311-1316
        • Tsui C.K.
        • Rice T.M.
        • Pande S.
        Predictors of nonstandard helmet use among San Francisco Bay-area motorcyclists.
        Traffic Inj Prev. 2014; 15: 151-155
        • Khan I.
        • Khan A.
        • Aziz F.
        • et al.
        Factors associated with helmet use among motorcycle users in Karachi, Pakistan.
        Acad Emerg Med. 2008; 15: 384-387
        • Pham K.H.
        • Le Thi Q.X.
        • Petrie D.J.
        • et al.
        Households' willingness to pay for a motorcycle helmet in Hanoi, Vietnam.
        Appl Health Econ Health Pol. 2008; 6: 137-144
        • Ranney M.L.
        • Mello M.J.
        • Baird J.B.
        • et al.
        Correlates of motorcycle helmet use among recent graduates of a motorcycle training course.
        Accid Anal Prev. 2010; 42: 2057-2062
        • Akaateba M.A.
        • Yakubu I.
        • Akanbang B.A.
        Correlates and barriers associated with motorcycle helmet use in wa, Ghana.
        Traffic Inj Prev. 2015; 16: 809-817
        • Fong M.C.
        • Measelle J.R.
        • Dwyer J.L.
        • et al.
        Rates of motorcycle helmet use and reasons for non-use among adults and children in Luang Prabang, Lao People's Democratic Republic.
        BMC Publ Health. 2015; 15: 970
        • Karuppanagounder K.
        • Vijayan A.V.
        Motorcycle helmet use in Calicut, India: user behaviors, attitudes, and perceptions.
        Traffic Inj Prev. 2016; 17: 292-296
        • Bachani A.M.
        • Hung Y.W.
        • Mogere S.
        • et al.
        Helmet wearing in Kenya: prevalence, knowledge, attitude, practice and implications.
        Publ Health. 2017; 144S: S23-S31
        • McKnight A.J.
        • McKnight A.S.
        The effects of motorcycle helmets upon seeing and hearing.
        Accid Anal Prev. 1995; 27: 493-501
        • Bogerd C.P.
        • Walker I.
        • Bruhwiler P.A.
        • Rossi R.M.
        The effect of a helmet on cognitive performance is, at worst, marginal: a controlled laboratory study.
        Appl Ergon. 2014; 45: 671-676
        • Chiou M.
        • Wickremasinghe W.
        • Kache S.
        • Tennakoon L.
        Barriers to using motorcycle helmets among children between 3 and 18 Years old in kurunegala district of Sri Lanka: a descriptive study of use, knowledge, attitudes, and practices.
        Pediatrics. 2018; 141
        • Siddiqui S.
        • Arora S.
        • Peipert J.
        • et al.
        Survey of helmet influences of female pillions in New Delhi.
        J Surg Res. 2013; 184: 404-410
        • World Bank Development Indicators
        Time Series: Two-Wheelers (Per 1,000 People).
        World Bank, 2005 (2005 [updated December 2019November 12, 2021]. Available from:)
        • Callcut R.A.
        • Raja A.S.
        • Como J.J.
        • et al.
        Writing an EAST Practice Management Guideline (PMG): A Step-by-step How-To-Guide.
        2016 ([updated October 2016October 29, 2021]. Available from:)
        • Road Traffic Injuries Research Network Multicenter Study C.
        • Ackaah W.
        • Afukaar F.
        • et al.
        The use of non-standard motorcycle helmets in low- and middle-income countries: a multicentre study.
        Inj Prev. 2013; 19: 158-163
        • von Hippel P.T.
        The heterogeneity statistic I(2) can be biased in small meta-analyses.
        BMC Med Res Methodol. 2015; 15: 35