Women and Men Use Different Strategies to Stabilize the Head in Response to Impulsive Loads: Implications for Concussion Injury Risk

Architecture of head and neck soft tissues and associated entheses: An exploration of sexual dimorphism in, and population differences between, New Zealand and Thai individuals

Understanding the musculoskeletal anatomy of soft tissues of the head and neck is important for surgical applications, biomechanical modelling and management of injuries, such as whiplash. Additionally, analysing sex and population differences in cervical anatomy can inform how biological sex and population variation may impact these anatomical applications. Although some muscles of the head and neck are well-studied, there is limited architectural information that also analyses sex and population variation, for many small cervical soft tissues (muscles and ligaments) and associated entheses (soft tissue attachment sites). Therefore, the aim of this study was to present architectural data (e.g., proximal and distal attachment sites, muscle physiological cross-sectional area, ligament mass, enthesis area) and analyse sex and population differences in soft tissues and entheses associated with sexually dimorphic landmarks on the cranium (nuchal crest and mastoid process) and clavicle (rhomboid fossa). Through the dissection and three-dimensional analysis of 20 donated cadavers from New Zealand (five males, five females; mean age 83 ± 8 years; range 67-93 years) and Thailand (five males, five females; 69 ± 13 years; range 44-87 years), the following soft tissues and their associated entheses were analysed: upper trapezius, semispinalis capitis and the nuchal ligament (nuchal crest); sternocleidomastoid, splenius capitis and longissimus capitis (mastoid process); the clavicular head of pectoralis major, subclavius, sternohyoid and the costoclavicular (rhomboid) ligament (rhomboid fossa). Findings indicate that although muscle, ligament and enthesis sizes were generally similar to previously published data, muscle size was smaller for six of the eight muscles in this study, with only the upper trapezius and subclavius demonstrating similar values to previous studies. Proximal and distal attachment sites were largely consistent with the current research. However, some individuals (six of 20) had proximal upper trapezius attachments on the cranium, with most attaching solely to the nuchal ligament, contrasting with existing literature, which often describes attachment to the occipital bone. With respect to sexual dimorphism, the Thai sample exhibited more sex differences in muscle size than the New Zealand sample, but for enthesis size (area), both samples had the same amount of statistically significant sex differences (5 of 10). Additionally, some significant population differences were found when comparing muscle and enthesis size data between the New Zealand and Thai samples. Despite these findings, no sex or population differences were found for ligament size (mass) in either group. This paper presents new architectural data for several understudied areas of the head and neck, as well as providing analyses on sex and population differences, two areas that have limited representation in anatomy.

Sex-related differences in sternocleidomastoid muscle morphology in healthy young adults: A cross-sectional magnetic resonance imaging measurement study

BACKGROUND

Changes in sternocleidomastoid (SCM) muscle cross-sectional area (CSA) and volume may contribute to neck-related concussion symptoms and whiplash-associated disorders. Magnetic resonance imaging (MRI) data on healthy SCM morphology can provide information that may lead to targeted treatment protocols.

OBJECTIVES

To examine sex-related differences in MRI-based SCM CSA, SCM volume and neck area in healthy young adults, to analyze associations between measurements and participant variables and to assess inter-rater reliability for measurement quantification.

DESIGN

Cross-sectional study.

METHODS

13 males and 14 females underwent MRI scans. Slices obtained from C3-C7 were analyzed by three raters. SCM CSA at C4, total SCM volume from C3-C7 and neck area at C4 were quantified. Measurements were calculated as absolute and normalized values by body mass. Multivariable regression was used to analyze associations between normalized measurement values and participant variables. Inter-rater reliability was determined using intraclass correlation coefficients (ICC).

RESULTS

Females had significantly lower normalized overall average SCM CSA (mean difference 1.3 mm²/kg (95% CI 0.4-2.2, p = 0.006) and total SCM volume (mean difference 140.8 mm3/kg (95% CI 66.1-215.5, p < 0.001) than males. Regression models indicated female sex was associated with lower normalized overall average SCM CSA (p = 0.004) and total SCM volume (p < 0.001). Inter-rater reliability was excellent for SCM CSA (ICC_3,3 = 0.909), SCM volume (ICC_3,3 = 0.910) and neck area (ICC_3,3 = 0.995).

CONCLUSIONS

These results enhance our understanding of sex-related differences in SCM morphology and will inform future research and clinical practice related to cervical muscle injury.

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

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.

The Effect of the FIFA 11 + with Added Neck Exercises on Maximal Isometric Neck Strength and Peak Head Impact Magnitude During Heading: A Pilot Study

BACKGROUND

Higher neck strength has been postulated to reduce head impact magnitude during purposeful heading in football.

OBJECTIVES

This pilot trial explored the effect of a neck exercise programme on (1) neck strength and (2) head impact magnitude during heading in male and female adolescent football players.

METHODS

Boys and girls (aged 12-17 years) were randomised by team to the intervention (5 weeks of supervised neuromuscular neck exercises integrated into part 2 of the FIFA 11 + , completed three times per week) or the control group (usual part 2 of the FIFA 11 + , no neck exercises). Outcomes included isometric neck strength and head impact magnitude (peak linear acceleration and peak angular velocity) during standardised heading from a throw-in (at baseline and 6 weeks) plus completion of an evaluation survey by intervention players and coaches.

RESULTS

In total, 52 players (n = 31 intervention; n = 21 control) completed the study. Mixed-model analysis of variance (ANOVA) revealed significant differences in neck strength variables (p < 0.001), peak linear acceleration (p = 0.04) and peak angular velocity (p = 0.04) between the intervention and control groups over time. Intervention players demonstrated increases in mean composite neck strength (53.8% intervention vs 15.6% control) as well as decreases in mean peak linear head acceleration during heading (- 11.8% vs - 5.0%) from baseline to follow-up. Reduction in peak angular velocity was more pronounced in girls (- 27.7%) than boys (- 11.5%) in the intervention group. The addition of neck exercises into part 2 of the FIFA 11 + was feasible and accepted by players and coaches.

CONCLUSION

On average, players who completed neck exercises demonstrated an increase in isometric neck strength and a decrease in head impact magnitude during heading. These exercises were easily incorporated into usual training. Australian New Zealand Clinical Trials Registry (no: ACTRN12619001375145).

Cervical Muscle Activation Characteristics and Head Kinematics in Males and Females Following Acoustic Warnings and Impulsive Head Forces

Sex, head and neck posture, and cervical muscle preparation are contributing factors in the severity of head and neck injuries. However, it is unknown how these factors modulate the head kinematics. In this study, twenty-four (16 male and 8 female) participants experienced 50 impulsive forces to their heads with and without an acoustic warning. Female participants demonstrated a 71 ms faster (p = 0.002) muscle activation onset compared to males after warning. The magnitude of muscle activation was not significant between sexes. Females exhibited 21% (p < 0.008) greater peak angular velocity in all force directions and 18% (p < 0.04) greater peak angular acceleration in sagittal plane compared to males. Females exhibited 15% (p = 0.03) greater peak linear acceleration compared to males only in sagittal flexion. Preparation attenuated head kinematics significantly (p < 0.03) in 11 out of 18 investigated head kinematics for both sexes. A warning eliciting a startle response 420 ms prior to the impact resulted in significant attenuation of all measured head kinematics in sagittal extension (p < 0.037). In conclusion, both sex and warning type were significant factors in head kinematics. These data provide insight into the complex relationship of muscle activation and sex, and may help identify innovative strategies to reduce head and neck injury risk in sports.

Deep and superficial cervical muscles respond differently to unstable motor skill tasks

Biomechanical modelling and physiological studies suggest that various spinal muscle layers differ in their contribution to spine movement and stiffness. This study aimed to investigate the activation of deep and superficial muscles in stable and unstable task conditions. Nine healthy participants performed a task of controlling a metal ball on a plate fixed to the head in seated position. In unstable tasks, visual feedback was provided by mirrors to move the ball to the centre of the plate by small head movements and maintain the position for 3 s. Task difficulty was adjusted in a stepwise progression of difficulty using five surfaces with materials of decreasing resistance. In the stable condition, the ball was fixed to the plate's centre. EMG was recorded with surface (sternocleidomastoid, anterior scalenes, upper trapezius) and fine-wire electrodes (rectus capitis posterior major, obliquus inferior, multifidus, semispinalis cervicis, splenius capitis). The outcome variable was root mean square (RMS) EMG during the part of the task when the ball was maintained in the centre position. Results revealed greater cervical muscle activity in the unstable than stable conditions (p < 0.001, η_p² = 0.746). Control of deep and superficial cervical muscles differed (p = 0.003, η_p² = 0.354). Deep cervical muscle activity was greater with unstable tasks, but did not differ with task difficulty. In contrast, superficial cervical muscle activity increased in a stepwise manner with increasing challenge. These results support the notion that the central nervous system uses different strategies for control of deep versus superficial muscle layers of the cervical spine in association with instability.

The role of neck muscle co-contraction and postural changes in head kinematics after safe head impacts: Investigation of head/neck injury reduction

Concerns surrounding concussions from impacts to the head necessitate research to generate new knowledge about ways to prevent them and reduce risk. In this paper, we report the relative temporal characteristics of the head resulting from neck muscle co-contraction and postural changes following a sudden force applied to the head in four different directions. In the two "prepared" conditions (i.e., co-contraction and postural), participants experienced impulsive forces to the head after hearing a warning. The warning given for the postural condition informed both the direction and timing of the impulsive force. Participants responded to the postural warning by altering their head posture, whereas in the co-contraction warning, the force direction was unknown to them, and they were asked to isometrically co-contract their neck muscles after the warning. Peak angular velocity reduced by 29% in sagittal extension, 18% in sagittal flexion, and 23% in coronal lateral flexion in prepared vs. unwarned conditions. Peak linear acceleration was attenuated by 15% in sagittal extension, 8% in sagittal flexion, and 18% in coronal lateral flexion in prepared vs. unwarned conditions. Changes in peak angular acceleration were not uniform. We also measured a significant delay in the peak angular velocity (22 vs. 44.8 ms) and peak angular acceleration (7 vs. 20 ms) after peak linear acceleration in prepared compared to unwarned conditions. An increase in muscle activation significantly reduced the peak angular velocity and linear acceleration. Gross head movement was significantly decreased with preparation. These findings suggest that a warning prior to impact can reduce head kinematics associated with injury.

Sex differences in neck strength and head impact kinematics in university rugby union players

Globally, over three million women participate in rugby union, yet injury prevention and training strategies are predominantly based on androcentric data. These strategies may have limited generalisability to females, given the cervical spine is more susceptible to whiplash and less adept at resisting inertial loading. A total of 53 university rugby union players (25 female, 28 male, 20.7 ± 1.8 years) had their isometric neck strength measured. Bespoke instrumented mouthguards were used to record the magnitude of head impact events in six female and seven male competitive matches. Mean female maximal isometric neck strength was 47% lower than male. Independent samples Mann-Whitney U tests showed no significant differences for peak linear head acceleration (female: median 11.7 g, IQR 7.9 g; male: median 12.5 g, IQR 7.0 g p=.23) or peak rotational head acceleration (female: median 800.2 rad·s^-2, IQR 677.7 rad·s^-2; male: median 849.4 rad·s^-2, IQR 479.8 rad·s^-2; p=.76), despite the mean male body mass being 24% greater than female. Coded video analysis revealed substantial differences in head-impact mechanisms; uncontrolled whiplash dominated >50% of all recorded female impact events and <0.5% in males. Direct head-to-ground impacts comprised 26.1% of female and 9.7% of male impacts, with whiplash occurring in 78.0% and 0.5%, respectively. Overall, the data provided in this study do not support the generalisation of male-derived training and injury-prevention data to female rugby athletes. These results suggest a considerable research effort is required to identify specific weakness of female rugby players and derive appropriate training, injury prevention and return to play protocols.

Identifying degenerative effects of repetitive head trauma with neuroimaging: a clinically-oriented review

BACKGROUND AND SCOPE OF REVIEW

Varying severities and frequencies of head trauma may result in dynamic acute and chronic pathophysiologic responses in the brain. Heightened attention to long-term effects of head trauma, particularly repetitive head trauma, has sparked recent efforts to identify neuroimaging biomarkers of underlying disease processes. Imaging modalities like structural magnetic resonance imaging (MRI) and positron emission tomography (PET) are the most clinically applicable given their use in neurodegenerative disease diagnosis and differentiation. In recent years, researchers have targeted repetitive head trauma cohorts in hopes of identifying in vivo biomarkers for underlying biologic changes that might ultimately improve diagnosis of chronic traumatic encephalopathy (CTE) in living persons. These populations most often include collision sport athletes (e.g., American football, boxing) and military veterans with repetitive low-level blast exposure. We provide a clinically-oriented review of neuroimaging data from repetitive head trauma cohorts based on structural MRI, FDG-PET, Aβ-PET, and tau-PET. We supplement the review with two patient reports of neuropathology-confirmed, clinically impaired adults with prior repetitive head trauma who underwent structural MRI, FDG-PET, Aβ-PET, and tau-PET in addition to comprehensive clinical examinations before death.

REVIEW CONCLUSIONS

Group-level comparisons to controls without known head trauma have revealed inconsistent regional volume differences, with possible propensity for medial temporal, limbic, and subcortical (thalamus, corpus callosum) structures. Greater frequency and severity (i.e., length) of cavum septum pellucidum (CSP) is observed in repetitive head trauma cohorts compared to unexposed controls. It remains unclear whether CSP predicts a particular neurodegenerative process, but CSP presence should increase suspicion that clinical impairment is at least partly attributable to the individual's head trauma exposure (regardless of underlying disease). PET imaging similarly has not revealed a prototypical metabolic or molecular pattern associated with repetitive head trauma or predictive of CTE based on the most widely studied radiotracers. Given the range of clinical syndromes and neurodegenerative pathologies observed in a subset of adults with prior repetitive head trauma, structural MRI and PET imaging may still be useful for differential diagnosis (e.g., assessing suspected Alzheimer's disease).

Considering Biological Sex in Traumatic Brain Injury

Published epidemiological studies of traumatic brain injury (TBI) of all severities consistently report higher incidence in men. Recent increases in the participation of women in sports and active military service as well as increasing awareness of the very large number of women who sustain but do not report TBI as a result of intimate partner violence (IPV) suggest that the number of women with TBI is significantly larger than previously believed. Women are also grossly under-represented in clinical and natural history studies of TBI, most of which include relatively small numbers of women, ignore the role of sex- and age-related gonadal hormone levels, and report conflicting results. The emerging picture from recent studies powered to detect effects of biological sex as well as age (as a surrogate of hormonal status) suggest young (i.e., premenopausal) women are more likely to die from TBI relative to men of the same age group, but this is reversed in the 6th and 7th decades of life, coinciding with postmenopausal status in women. New data from concussion studies in young male and female athletes extend this finding to mild TBI, since female athletes who sustained mild TBI are significantly more likely to report more symptoms than males. Studies including information on gonadal hormone status at the time of injury are still too scarce and small to draw reliable conclusions, so there is an urgent need to include biological sex and gonadal hormone status in the design and analysis of future studies of TBI.

The clinical utility of the cervical vestibular-evoked myogenic potential (cVEMP) in university-level athletes with concussion

INTRODUCTION

Concussion is defined as a mild traumatic brain injury that can occur in all sport activities. Cervical vestibular-evoked myogenic potentials (cVEMPs) are accepted to demonstrate the vestibulocollic reflex. MAIN: To evaluate subclinical cervical abnormalities in the vestibulospinal pathway in subjects with concussion history with and without related symptoms via evoked vestibular potential.

METHODS

Monaurally air conduction cVEMP (500 Hz tone bursts) at intensity of 100 dBnHL and 200 sweeps. All responses were replicated.

RESULTS

One hundred fifty-four participants were initially tested; however, three (03) participants did not produce usable data (no response) and were eliminated for the dataset cutoff values analysis, being considered just as abnormal response. One hundred fifty-one responses consisted of 45 non-athlete individuals without any history of a concussion or concussion symptoms (normative group), 45 athletes without any history of a concussion or concussion symptoms (control group), 33 athletes with a history of at least one concussion but no concussion symptoms related (history group), and 28 athletes with a history of at least one concussion and concussion symptoms (symptoms group). The history and symptoms groups had statistically higher latency scores than the control and the normative groups. The Index Ratio data and Threshold data did not produce a significant effect for four groups. But, a pattern of abnormal cVEMP was found when comparing those without a history of concussion (0% abnormal response) versus the history group (24%) and symptoms group (32.3%).

CONCLUSION

The study provides data which supports the positive impact of cVEMP when evaluating athletes and identifying concussion processes.

Dry Needling and Acupuncture in Treatment of Dance-Related Injuries, MD, and PT Perspectives

Dancers frequently present to health care professionals with musculoskeletal impairments. The role of the health care practitioner, whether physician, physical therapist, or acupuncturist, is to decrease pain and restore function in the short term and to restore adaptive potential and neural connectivity in the long term. When dysfunction is treated, pain improves. Acupuncture and dry needling improve tissue perfusion by improving vasomotor control and can improve strength by removing motor inhibition. Acupuncture and dry needling are safe, complementary modalities aimed at improving the function of the dancer.

How Do We Meet the Challenges of Assessing and Managing Concussion?

Despite advances in the assessment, diagnosis, prognosis, and management of the patient with mild traumatic brain injury (mTBI) or concussion, the condition continues to frustrate clinicians and researchers. The November 2019 special issue of the Journal of Orthopaedic & Sports Physical Therapy (JOSPT) supports and represents an interdisciplinary approach to assessment, management, and treatment of mTBI/concussion. The articles further highlight the evolving role of the physical therapist throughout the clinical course post concussion. It is with gratitude to the authors who contributed to this special issue of JOSPT that we present the evidence and practices currently available to clinicians in the assessment and treatment of mTBI/concussion. J Orthop Sports Phys Ther 2019;49(11):766-767. doi:10.2519/jospt.2019.0107.

Should you let your child play football? What about soccer or hockey?

College students (n = 120) answered 18 yes-no questions that varied the child's gender (male, female), grade (grade school, high school, college), and sport (football, soccer, hockey). The format of the 18 yes or no questions was "If you had a child in (grade school, high school, college) would you let (him, her) play (football, soccer, hockey)"? Similar to a previous study, a large percentage (78.8%) of the respondents answered yes to the questions about football, indicating that they would permit their children to play football despite the risk of concussion (96% yes for male children, 67% yes for female children). Although the number of respondents who would allow their male child to play soccer (98% for male children, 99% for female children) or hockey (92% for male children, 89% for female children) was similar to the percentage of respondents that would allow their male child to play football, significantly more respondents would allow their female child to play soccer or hockey than football. This result is potentially problematic because soccer and hockey have high rates of concussion, especially for females, which suggests that the respondents may have been unaware of this fact.