Head and Neck Characteristics as Risk Factors For and Protective Factors Against Mild Traumatic Brain Injury in Military and Sporting Populations: A Systematic Review

Abstract

Background Investigators have proposed that various physical head and neck characteristics, such as neck strength and head and neck size, are associated with protection from mild traumatic brain injury (mTBI/concussion). Objectives To systematically review the literature and investigate potential relationships between physical head and neck characteristics and mTBI risk in athletic and military populations. Methods A comprehensive search of seven databases was conducted: MEDLINE, EMBASE, CINAHL, Scopus, SPORTDiscus, Cochrane Library, and Web of Science. Potential studies were systematically screened and reviewed. Studies on military and athletic cohorts were included if they assessed the relationship between physical head-neck characteristics and mTBI risk or proxy risk measures such as head impact kinematics. Results The systematic search yielded a total of 11,723 original records. From these, 22 studies met our inclusion criteria (10 longitudinal, 12 cross-sectional). Relevant to our PECO (Population, Exposure, Comparator, and Outcomes) question, exposures included mTBI incidence and head impact kinematics (acceleration, velocity, displacement) for impacts during sport play and training and in controlled laboratory conditions. Outcome characteristics included head and neck size (circumference, mass, length, ratios between these measures), neck strength and endurance, and rate of force development of neck muscles. Discussion We found mixed evidence for head and neck characteristics acting as risk factors for and protective factors against mTBI and increased susceptibility to head impacts. Head-neck strength and size variables were at times associated with protection against mTBI incidence and reduced impact kinematics (14/22 studies found one or more head-neck variable to be associated with protection); however, some studies did not find these relationships (8/22 studies found no significant associations or relationships). Interestingly, two studies found stronger and larger athletes were more at risk of sustaining high impacts during sport. Strength and size metrics may have some predictive power, but impact mitigation seems to be influenced by many other variables, such as behaviour, sex, and impact anticipation. A meta-analysis could not be performed due to heterogeneity in study design and reporting. Conclusion There is mixed evidence in the literature for the protective capacity of head and neck characteristics. We suggest field-based mTBI research in the future should include more dynamic anthropometric metrics, such as neck stiffness and response to perturbation. In addition, laboratory-based mTBI studies should aim to standardise design and reporting to help further uncover these complicated relationships.

Prevention of sports-related concussion in soccer: a comprehensive review of the literature

“…Neck strength as well as head and neck size are head and neck physical characteristics associated with protection against mild traumatic brain injury (mTBI) 5 . mTBI protection and altered impact kinematics are occasionally associated with head–neck size and strength variations.…”

“…According to a correlation between size and neck strength, a one-pound increase in neck strength reduces the risk of mTBI in high school athletes by 5% 31 . When comparing the sexes, neck strength significantly reduces the angular acceleration and displacement of the head during a disturbance 5 .…”

“…When a player heads the ball with a greater effective body mass, which is influenced by the player’s size, strength, and technique, the level of safety is significantly enhanced. Even with today’s youth-sized balls, smaller, younger players are more susceptible to potentially dangerous headers due to their lower body mass 5 .…”

“…discovered a significant correlation between neck strength and size in the prevention of mTBI in high school athletes, indicating that the risk of mTBI decreased by 5% for every pound of increased neck strength 31 . Neck strength significantly reduces head angular acceleration and disturbance displacement 5 . Reduced head kinematic response to external forces is associated with increased neck strength and anticipatory cervical muscle activation, which may aid in the prevention of concussions.…”

Acute effects of an isometric neck warm-up programme on neck performance characteristics and ultrasound-based morphology

“…Of these characteristics investigated, the neck warm-up was most effective improving rate of force development as the average improvement was 13% while visual-motor reaction time and peak forces were mostly non-significant ( p = 0.060 − 0.940) except left lateral flexion peak force ( p = 0.037). Recent meta-analyses indicated mixed findings on relationship between greater neck strength and mTBI [ 23 , 24 ]. Coaches and athletes should be informed that concussive forces could be mitigated by several factors such as anticipation and stiffness of neck musculatures as well as passive structures such as ligaments [ 25 ].…”