Passive cervical spine ligaments provide stability during head impacts

An Extended Neck Position is Likely to Produce Cervical Spine Injuries Through Buckling in Accidental Head-First Impacts During Rugby Tackling

Catastrophic cervical spine injuries in rugby often occur during tackling. The underlying mechanisms leading to these injuries remain unclear, with neck hyperflexion and buckling both proposed as the causative factor in the injury prevention literature. The aim of this study was to evaluate the effect of pre-impact head-neck posture on intervertebral neck loads and motions during a head-first rugby tackle. Using a validated, subject-specific musculoskeletal model of a rugby player, and computer simulations driven by in vivo and in vitro data, we examined the dynamic response of the cervical spine under such impact conditions. The simulations demonstrated that the initial head-neck sagittal-plane posture affected intervertebral loads and kinematics, with an extended neck resulting in buckling and supraphysiologic intervertebral shear and flexion loads and motions, typical of bilateral facet dislocation injuries. In contrast, an initially flexed neck increased axial compression forces and flexion angles without exceeding intervertebral physiological limits. These findings provide objective evidence that can inform injury prevention strategies or rugby law changes to improve the safety of the game of rugby.

Examining the influence of the Get aHEAD Safely in Soccer™ program on head impact kinematics and neck strength in female youth soccer players

The objective was to examine the efficacy of the Get aHEAD Safely in Soccer™ intervention on head impact kinematics and neck strength in female youth soccer players. The control group (CG) consisted of 13 players (age: 11.0 ± 0.4 yrs), while the experimental group (EG) consisted of 14 players (age: 10.6 ± 0.5 yrs). Head impact kinematics included peak linear acceleration (PLA), peak rotational acceleration (PRA), and peak rotational velocity (PRV). Pre- and post-season measures included strength measures of neck/torso flexion (NF/TF) and extension (NE/TE). Data were analysed using a multilevel linear model and ANOVA techniques. No differences in PLA, PRA, or PRV were observed between groups. The EG showed significant improvement in NF strength while the CG showed significant improvement in NE strength. Both groups significantly improved in TF pre- to post-season. The foundational strength components of the Get aHEAD Safely in Soccer program appear to show a benefit in youth soccer players beginning to learn the skill of purposeful heading.

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

OBJECTIVE

Athletic performance can be enhanced immediately after an isometric warm-up, a phenomenon termed post-activation performance enhancement (PAPE). While isometric warm-ups can improve lower extremity sprint and jump performance, neck-specific isometric warm-ups need development and validation for mild traumatic brain disorders and neck pain. This study examined acute effects of isometric warm-ups on neck performance and morphology.

METHODS

Arm 1: Twenty-six adults (13 M:13F) completed neck performance testing before and after a 10-minute neck isometric warm-up or stationary bike (sham) between two visits. Testing included visual-motor reaction time, peak force, rate of force development, force steadiness, and force replication/proprioception measured by a 6-axis load cell. An inclinometer assessed range-of-motion. Paired t-tests and two-way ANOVA examined effects of neck/bike warm-up and interaction effects, respectively. Arm 2: 24 adults (11 M:13F) completed ultrasound scans of cervical muscles: before 20-minute rest (sham), and before/after a 5-min neck isometric warm-up. Longus colli cross-sectional area and sternocleidomastoid/upper trapezius thickness and stiffness, and cervical extensors thickness was assessed. One-way ANOVA compared morphological values at sham, before, and after warm-up. Significance was set at p < 0.05.

RESULTS

Isometric neck warm-up increased rate of force development in flexion (p = 0.022), extension (p = 0.001-0.003), right lateral flexion (p = 0.004-0.032), left lateral flexion (p = 0.005-0.014), while peak force improved only in left lateral flexion (p = 0.032). Lateral flexion range-of-motion increased after neck warm-up (p = 0.003-0.026). Similarly, longus colli cross-sectional area (p = 0.016) and sternocleidomastoid thickness (p = 0.004) increased.

CONCLUSIONS

Increased neck performance characteristics and morphology are likely due to PAPE effects of isometric neck warm-up. For coaches and athletes, simple isometric contractions could be added to existing warm-ups to reduce prevalence, incidence, and severity of mild traumatic brain injuries and neck pain.

Evaluation of surface electromyography of selected neck muscles during the whiplash mechanism in aware and unaware conditions due to safe punching in kickboxing

BACKGROUND

Kickboxing is considered as a combat sport in progress, in which injuries are frequent and significant, and close injury monitoring is highly recommended. Sports injuries to the head and neck are estimated to cause 70% deaths and 20% permanent disabilities although they are much less common than those to the limbs. Whiplash mechanism involves the rapid extension (opening) and flexion (bending) of neck. The purpose of the current study was to investigate the electromyographic activity of selected muscles in the whiplash mechanism in aware and unaware conditions of the safe punching in kickboxing so that we can design special exercises.

METHOD

In the present study, 24 male kickboxing athletes aged 18-40 years were selected based on a purposive sampling method. The surface electromyography (EMG) signals of muscles were recorded with and without awareness of safe punching by using a nine-channel wireless EMG device. Additionally, a nine-channel 3D inertial measurement unit (IMU, wireless,) was utilized to determine the acceleration, kinematics, and angular velocity of the subjects' head. The statistical dependent t-test was applied to compare the EMG activity of each muscle, as well as its participation ratio.

RESULTS

The results of statistical analysis represented a significant increase in the EMG activity of sternocleidomastoid (p = 0.001), upper trapezius (p = 0.001) and cervical erector spinae muscles (p = 0.001), as well as the neck extension and flexion angles between the athletes aware (open eyes) and unaware (closed eyes) of the safe punching.

CONCLUSION

In this study, the EMG activity of the sternocleidomastoid, upper trapezius, and cervical erector spine muscles in the aware condition was significantly different from the activity under unaware condition. In fact, the intended muscles exhibited significantly different behaviors in preventing extension and flexion in the two conditions.

Effects of breathing reeducation on cervical and pulmonary outcomes in patients with non specific chronic neck pain: A double blind randomized controlled trial

OBJECTIVE

The purpose of this randomized controlled trial was to study effects of breathing reeducation in the treatment of patients with non specific chronic neck pain.

METHODS

A total of sixty eight eligible patients with chronic neck pain were randomly allocated to breathing reeducation (BR) group (n = 34) and routine physical therapy (RPT) group (n = 34). Clinical outcomes were neck pain measured through visual analogue score, cervical active range of motion through CROM device, strength of neck muscles through hand held dynamometer and endurance of neck muscles measured through craniocervical flexion test. The neck disability was measured through neck disability index (NDI) and pulmonary outcomes such as forced vital capacity (FVC), forced expiratory volume in one second (FEV1), and FEV1/FVC ratio were measured through Spirolab 4. The outcomes were assessed at baseline and at 4 and at 8 weeks from baseline.

RESULTS

There were significant improvements in the BR group compared with the RPT group (P = 0.002) for cervical flexion, extension (P = 0.029), endurance (P = 0.042), strength of neck flexors (P <0.001), neck extensors (P = 0.034). Likewise there was a significant change in NDI (P = 0.011), FEV1 (P = 0.045), FVC (P <0.001), and FEV1/FVC ratio (P <0.001) in the BR group compared with the RPT group. The cervical side flexion and rotation showed no significant difference in breathing reeducation group with p > 0.05.

CONCLUSION

Breathing reeducation combined with routine physical therapy is an effective treatment in patients with non specific chronic neck pain.

TRIAL REGISTRATION

IRCT 20200226046623N1, https://www.irct.ir/trial/46240.

Electromyography-Assisted Neuromusculoskeletal Models Can Estimate Physiological Muscle Activations and Joint Moments Across the Neck Before Impacts

Knowledge of neck muscle activation strategies before sporting impacts is crucial for investigating mechanisms of severe spinal injuries. However, measurement of muscle activations during impacts is experimentally challenging and computational estimations are not often guided by experimental measurements. We investigated neck muscle activations before impacts with the use of electromyography (EMG)-assisted neuromusculoskeletal models. Kinematics and EMG recordings from four major neck muscles of a rugby player were experimentally measured during rugby activities. A subject-specific musculoskeletal model was created with muscle parameters informed from MRI measurements. The model was used in the calibrated EMG-informed neuromusculoskeletal modeling toolbox and three neural solutions were compared: (i) static optimization (SO), (ii) EMG-assisted (EMGa), and (iii) MRI-informed EMG-assisted (EMGaMRI). EMGaMRI and EMGa significantly (p < 0.01) outperformed SO when tracking cervical spine net joint moments from inverse dynamics in flexion/extension (RMSE = 0.95, 1.14, and 2.32 N·m) but not in lateral bending (RMSE = 1.07, 2.07, and 0.84 N·m). EMG-assisted solutions generated physiological muscle activation patterns and maintained experimental cocontractions significantly (p < 0.01) outperforming SO, which was characterized by saturation and nonphysiological "on-off" patterns. This study showed for the first time that physiological neck muscle activations and cervical spine net joint moments can be estimated without assumed a priori objective criteria before impacts. Future studies could use this technique to provide detailed initial loading conditions for theoretical simulations of neck injury during impacts.

Cervical spine injury response to direct rear head impact

BACKGROUND

Direct rear head impact can occur during falls, road accidents, or sports accidents. They induce anterior shear, flexion and compression loads suspected to cause flexion-distraction injuries at the cervical spine. However, post-mortem human subject experiments mostly focus on sled impacts and not direct head impacts.

METHODS

Six male cadavers were subjected to a direct rear head impact of 3.5 to 5.5 m/s with a 40 kg impactor. The subjects were equipped with accelerometers at the forehead, mouth and sternum. High-speed cameras and stereography were used to track head displacements. Head range of motion in flexion-extension was measured before and after impact for four cadavers. The injuries were assessed from CT scan images and dissection.

FINDINGS

Maximum head rotation was between 43 degrees and 78 degrees, maximum cranial-caudal displacement between -12 mm and - 196 mm, and antero-posterior displacement between 90 mm and 139 mm during the impact. Four subjects had flexion-distraction injuries. Anterior vertebral osteophyte identification showed that fractures occurred at adjacent levels of osteophytic bridges. The other two subjects had no anterior osteophytes and suffered from C2 fracture, and one subject also had a C1-C2 subluxation. C6-C7 was the most frequently injured spinal level.

INTERPRETATION

Anterior vertebral osteophytes appear to influence the type and position of injuries. Osteophytes would seem to provide stability in flexion for the osteoarthritic cervical spine, but to also lead to stress concentration in levels adjacent to the osteophytes. Clinical management of patients presenting with osteophytes fracture should include neck immobilization and careful follow-up to ensure bone healing.

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.

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.

A Novel Neuromuscular Head-Neck Model and Its Application on Impact Analysis

OBJECTIVE

Neck muscle activation plays an important role in maintaining posture and preventing trauma injuries of the head-neck system, levels of which are primarily controlled by the neural system. Thus, the present study aims to establish and validate a neuromuscular head-neck model as well as to investigate the effects of realistic neural reflex control on head-neck behaviors during impact loading.

METHODS

The neuromuscular head-neck model was first established based on a musculoskeletal model by including neural reflex control of the vestibular system and proprioceptors. Then, a series of human posture control experiments was implemented and used to validate the model concerning both joint kinematics of the cervical spine and neck muscle activations. Finally, frontal impact experiments of varying loading severities were simulated with the newly established model and compared with an original model to investigate the influences of the implanted neural reflex controllers on head-neck kinematic responses.

RESULTS

The simulation results using the present neuromuscular model showed good correlations with in-vivo experimental data while the original model even cannot reach a correct balance status. Furthermore, the vestibular reflex is noted to dominate the muscle activation in less severe impact loadings while both vestibular and proprioceptive controllers have a lot of effect in higher impact loading severity cases.

CONCLUSIONS

In summary, a novel neuromuscular head-model was established and its application demonstrated the significance of the neural reflex control in predicting in vivo head-neck responses and preventing related injury risk due to impact loading.

Cervical Muscle Activation Due to an Applied Force in Response to Different Types of Acoustic Warnings

Mild traumatic brain injury (mTBI) and whiplash-associated disorder are the most common head and neck injuries and result from a sudden head or body acceleration. The head and neck injury potential is correlated with the awareness, level of muscle activation, and posture changes at the time of the perturbation. Environmental acoustic stimuli or a warning system can influence muscle activation and posture during a head perturbation. In this study, different acoustic stimuli, including Non-Directional, Directional, and Startle, were provided 1000 ms before a head impact, and the amplitude and timing of cervical muscle electromyographic (EMG) data were characterized based on the type of warning. The startle warning resulted in 49% faster and 80% greater EMG amplitude compared to the Directional and Non-Directional warnings after warning and before the impact. The post-impact peak EMG amplitudes in Unwarned trials were lower by 18 and 21% in the retraction and rebound muscle groups, respectively, compared to any of the warned conditions. When there was no warning before the impact, the retraction and rebound muscle groups also reached their maximum activation 38 and 54 ms sooner, respectively, compared to the warned trials. Based on these results, the intensity and complexity of information that a warning sound carries change the muscle response before and after a head impact and has implications for injury potential.

A one-dimensional collagen-based biomechanical model of passive soft tissue with viscoelasticity and failure

INTRODUCTION

Strains and sprains of soft tissues, including tendons and ligaments, are frequently occurring injuries. Musculoskeletal models show great promise in prediction and prevention of these injuries. However, these models rarely account for the viscoelastic properties of ligaments and tendons, much less their failure properties. The purpose of this project was to develop, simplify, and analyze a collagen-distribution model to address these limitations.

MODEL DEVELOPMENT

A distribution-moment approximation was applied to an existing partial differential equation model to reduce its computational complexity. The resulting model was equipped with a Voigt model in series, which endowed it with viscoelastic properties in addition to failure properties.

RESULTS

The model was able to reproduce the characteristic toe, linear, and failure regions ubiquitous throughout in-vitro tests on tissue specimens. In addition, it was able to reproduce a tri-phasic creep test consisting of an initial deformation, a steady-state, and failure. Stress-relaxation and hysteresis were also reproducible by the model.

DISCUSSION AND CONCLUSION

The ability to reproduce so many characteristics of biological tissues suggests more bio-fidelity was achieved by the reduced model was other currently available models. Future work to further improve its bio-fidelity is proposed for specific tendons and ligaments.

Estimating Trunk and Neck Stabilization for Avoiding Head Impact during Real-World Falls in Older Adults

In this work, we quantify the neck's involvement in stabilizing the head during falls in older adults to avoid head impacts. We tracked kinematics of 12 real-world backward falls in long-term care captured on video, where head impact was avoided. We estimated dynamic spring-dashpot parameters of the neck and hip representing active muscle activity and passive tissue structures. Neck stiffness, damping, and target posture averaged 24.00±6.17Nm/rad, 0.38±0.16Nms/rad, and 76.2±14.7° flexion respectively. The stiffness and target posture suggest that residents actively contracted their neck muscles to maintain the head upright. Our results shed light on the importance of neck strength for avoiding head impact during a fall.Clinical Relevance-Falls account for 80% of traumatic brain injuries in adults 65+ years. While upper limb bracing can reduce the risk of head impacts during a fall in young adults, this protective response is less effective in older adults living in longterm care. Understanding how the neck and torso musculature are used to avoid head impact can guide the design of therapeutic exercise programs and assistive or protective devices.

Vulnerable locations on the head to brain injury and implications for helmet design

In studying traumatic brain injury (TBI), it has been long hypothesized that the head is more vulnerable to injury from impacts in certain directions or locations, as the relationship between impact force and the resulting neurological outcome is complex and can vary significantly between individual cases. Many studies have identified head angular acceleration to be the putative cause of brain trauma, but it is not well understood how impact location can affect the resulting head kinematics and tissue strain. Here, we identify the susceptibility of the head to accelerations and brain strain from normal forces at contact points across the surface of the skull and jaw using a 3-dimensional, 20 degree-of-freedom rigid-body head and cervical spine model. We find that head angular acceleration and brain tissue strain resulting from an input force can vary by orders of magnitude based on impact location on the skull, with the mandible as the most vulnerable region. Conversely, head linear acceleration is not sensitive to contact location. Using these analyses, we present an optimization scheme to distribute helmet padding thickness to minimize angular acceleration, resulting in a reduction of angular acceleration by an estimated 25% at the most vulnerable contact point compared to uniform thickness padding. This work gives intuition behind the relationship between input force and resulting brain injury risk, and presents a framework for developing and evaluating novel head protection gear.