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.

Adoption of a research-based program for neck disorders implemented in primary care physiotherapy: a short- and long-term follow-up survey study.

Neck disorders are common in primary health care (PHC) physiotherapy. A neck-specific exercise program based on research findings was implemented among physiotherapists in Swedish PHC. The aim of the study was to evaluate the adoption of the program. We invited PHC physiotherapists to an educational session including theoretical information and practical training. Before the educational session the participants (n = 261) completed a baseline questionnaire. After 3 and 12 months, we distributed surveys to identify changes in practice and in confidence regarding diagnosis and treatment. We compared data from 3-months and 12-months follow-up, respectively, with baseline data. Self-reported frequency of most of the included assessment methods was unchanged after 12 months. Frequency of assessment of neck proprioception had increased significantly. Specific neck muscle exercise for treatment of whiplash associated disorders was applied more frequently after 3 and after 12 months than at baseline. Frequency of other treatment methods remained unchanged. Confidence in diagnosis and treatment increased significantly, particularly among women. The program was not adopted as expected, but resulted in increased confidence regarding diagnosis and treatment. The provision of a short educational session seemed not to be sufficient to obtain a sustained change in practice.

Lower neck injury criteria for THOR and Hybrid III dummies in rear impact.

OBJECTIVE: The objectives of the study are to derive lower-neck-injury probability curves under rear impact loading from matched pair Hybrid III and THOR dummy tests. METHODS: Twelve whole-body and 15 isolated head-neck rear-impact sled tests were conducted using the 2 dummies. They were positioned on a rigid seat that was attached to an acceleration sled. The dummies were positioned with the head parallel to the ground, torso against the seat back, and legs stretched such that there was no axial rotation. The acceleration pulse matched the previous in-house human cadaver tests. The 6-axis lower-neck load cell was used in both dummies. For the isolated rear-impact tests, the head-neck was excised from the dummies, and the lower-neck load cell was mounted to the top of the sled with the head parallel to the ground and such that the acceleration vector was in the rear impact mode. Lower-neck loads and lower-neck-injury criteria (LNij) were obtained using the load cell data and survival analysis was used to develop injury-assessment-risk values and curves for both dummies. The LNij criteria were determined for both dummies using the intercept value corresponding to the 90% probability level for the forces and moments. RESULTS: The lognormal and Weibull distributions were the optimal distributions for the Hybrid III and THOR devices. At the 50% risk level, the mean LNij was 1.1 and NCIS was 0.77 for the Hybrid III, and 1.5 and 0.30 for the THOR device. The quality indices were in the fair range and good range for the 2 dummies, respectively, at this risk level. CONCLUSIONS: The lower neck based LNij injury assessment risk curves and reference values, IARCs and IARVs, serve as the first dataset for injury assessments, and the THOR may be a better test device for assessing injures in rear impact environments.

Application of Simulation Methods in Cervical Spine Dynamics.

Neck injury is one of the most frequent spine injuries due to the complex structure of the cervical spine. The high incidence of neck injuries in collision accidents can bring a heavy economic burden to the society. Therefore, knowing the potential mechanisms of cervical spine injury and dysfunction is significant for improving its prevention and treatment. The research on cervical spine dynamics mainly concerns the fields of automobile safety, aeronautics, and astronautics. Numerical simulation methods are beneficial to better understand the stresses and strains developed in soft tissues with investigators and have been roundly used in cervical biomechanics. In this article, the simulation methods for the development and application of cervical spine dynamic problems in the recent years have been reviewed. The study focused mainly on multibody and finite element models. The structure, material properties, and application fields, especially the whiplash injury, were analyzed in detail. It has been shown that simulation methods have made remarkable progress in the research of cervical dynamic injury mechanisms, and some suggestions on the research of cervical dynamics in the future have been proposed.

Surface Contact Features, Impact Obliquity, and Preimpact Rotational Motion in Concussive Helmet-to-Ground Impacts: Assessment via a New Impact Test Device.

This paper reports the development of a test device for replicating unique features of concussion-causing helmet-to-ground impacts. Helmet-to-ground impacts are characterized by an oblique impact velocity vector, preimpact rotational motion of the helmeted head, and an impact into a compliant frictional surface of unknown effective mass. No helmet assessment testing program replicates these impact characteristics, yet they influence brain injury risk and therefore may influence helmet design priorities. To replicate these mechanics, the carriage of a drop tower was modified by the addition of a curvilinear bearing track and a hinged torso-neck fixture to which a helmeted head of a Hybrid III anthropomorphic test device was mounted. Preimpact rotational motion of the head was imparted by forcing a link arm to follow the curvilinear path as the carriage fell under gravity. At impact, the rotating helmeted head struck a vertically mounted surface. The ground impact features of head kinematics are illustrated by comparing rear impacts into a rigid, low-friction surface against those into a compliant frictional surface simulating turf. With the rigid, low-friction surface, the head experienced a change in rotational rate of approximately 40 rad/s, which corresponded to a peak rotational acceleration of approximately αy = - 4000 rad/s2. In contrast, peak rotational acceleration with the compliant frictional surface was approximately αy = - 1000 rad/s2 while the helmet was in contact with the surface. Neck loads were significantly greater with the compliant frictional surface. Translational head acceleration was less sensitive to the surface characteristics, with the peak of the anterior-posterior component essentially unchanged.

Pre-season screening of the upper body and trunk in Australian football players: A prospective study.

OBJECTIVE: To determine whether screening tests of upper body, trunk region, and of whole-body function could prospectively identify community AFL players who sustain in-season shoulder/head/neck injuries. Additionally, to present screening test reference values. DESIGN: Prospective cohort; SETTING: Community sport; PARTICIPANTS: 142 male community AFL players (range 15-37 years). MAIN OUTCOME MEASURES: (i) isometric shoulder external and internal rotation (ER/IR) strength; (ii) upper body combined elevation functional ROM; (iii/iv) whole-body functional jump ROM; (v) static thoracic spine angle; (vi) cervical joint proprioception, and (vii) trunk muscle size and function. Results were compared among players with (n = 21) and without (n = 121) an in-season shoulder, head, or neck injury. ROC analysis and odds ratios were used to determine the predictive values. RESULTS: Two screening tests predicted an in-season shoulder, head, or neck injury; dominant and non-dominant isometric ER strength (AUC 0.629, 95%CI 0.51-0.74; optimal cut point 182 N and AUC 0.619, 95%CI 0.50-0.74; optimal cut point 184 N, respectively). The adjusted odds ratio for the strongest predictor: dominant ER muscle strength was 6.02 (95%CI 1.8-19.9). CONCLUSION: Greater ER strength was associated with in-season shoulder/head/neck injuries in community AFL players; however, further research is required to determine the clinical significance of this finding.

Improving the staging of neck injuries using a new index, the Neck Functional Holistic Analysis Score: Clustering approach to determine degrees of impairment.

BACKGROUND: Traumatic cervical spine injuries are amongst the traffic injuries that can cause most harm to a person. Classifying subtypes of clinical presentations has been a method used in other pathologies to diagnose more efficiently and to address the appropriate treatment and the prognosis. The management of patients suffering from cervical injuries could be improved by classifying the severity of the impairment. This will allow clinicians to propose better treatment modalities according to the severity of the injury. MATERIALS AND METHODS: The present study is a retrospective cohort study performed with the clinical data from 772 patients stored at Fisi-(ON) Health Group. All the patients treated for cervical spine injuries are evaluated using the EBI-5® system, which is based on inertial measurement unit (IMU) technology. The normalized range of motion of each patient was incorporated into a single index, the Neck Functional Holistic Analysis Score (NFHAS). RESULTS: Clustering analysis of the patients according to their NFHAS resulted in five groups. The Kruskal-Wallis H test showed that there were statistically relevant differences in the ROM values and NFHAS of the patients depending on the cluster they were assigned to: FE X2(4) = 551.59, p = 0.0005; LB ROM X2(4) = 484.58, p = 0.0005; RT ROM X2(4) = 557.14, p = 0.0005; NFHAS X2(4) = 737.41, p = 0.0005. Effect size with ηp2 for the comparison of groups were: FE = 0.76, LB = 0.68, RT = 0.76 and NFHAS = 0.96. CONCLUSION: The NFHAS is directly correlated to the available ROM of the patient. The NFHAS serves as a good tool for the classification of cervical injury patients. The degree of impairment shown by the cervical injury can now be staged correctly using this new classification.

Comparison of three different methods to estimate the burden of disease of burn injuries in Western Australia in 2011-2018.

BACKGROUND: Priority setting and resource allocation in health care, surveillance and interventions is based increasingly on burden of disease. Several methods exist to calculate the non-fatal burden of disease of burns expressed in years lived with disability (YLDs). The aim of this study was to assess the burden of disease due to burns in Western Australia 2011-2018 and compare YLD outcomes between three existing methods. METHODS: Data from the Burns Service of Western Australia was used. Three existing methods to assess YLDs were compared: the Global Burden of Disease (GBD) method, a method dedicated to assess injury YLDs (Injury-VIBES), and a method dedicated to assess burns YLDs (INTEGRIS-burns). RESULTS: Incidence data from 2,866 burn patients were used. Non-fatal burden of disease estimates differed substantially between the different methods. Estimates for 2011-2018 ranged between 610 and 1,085 YLDs per 100.000 based on the Injury-VIBES method; between 209 and 324 YLDs based on the INTEGRIS-burns method; and between 89 and 120 YLDs based on the GBD method. YLDs per case were three to nine times higher when the Injury-VIBES method was applied compared to the other methods. Also trends in time differed widely through application of the different methods. There was a strong increase in YLDs over the years when the Injury-VIBES method was applied, a slight increase when the INTEGRIS-burns method was applied and a stable pattern when the GBD method was applied. CONCLUSION: This study showed that the choice for a specific method heavily influences the non-fatal burden of disease expressed in YLDs, both in terms of annual estimates as well as in trends over time. By addressing the methodological limitations evident in previously published calculations of the non-fatal burden of disease, the INTEGRIS-burns seems to present a method to provide the most robust estimates to date, as it is the only method adapted to the nature of burn injuries and their recovery.

A neck compression injury criterion incorporating lateral eccentricity.

There is currently no established injury criterion for the spine in compression with lateral load components despite this load combination commonly contributing to spinal injuries in rollover vehicle crashes, falls and sports. This study aimed to determine an injury criterion and accompanying tolerance values for cervical spine segments in axial compression applied with varying coronal plane eccentricity. Thirty-three human cadaveric functional spinal units were subjected to axial compression at three magnitudes of lateral eccentricity of the applied force. Injury was identified by high-speed video and graded by spine surgeons. Linear regression was used to define neck injury tolerance values based on a criterion incorporating coronal plane loads accounting for specimen sex, age, size and bone density. Larger coronal plane eccentricity at injury was associated with smaller resultant coronal plane force. The level of coronal plane eccentricity at failure appears to distinguish between the types of injuries sustained, with hard tissue structure injuries more common at low levels of eccentricity and soft tissue structure injuries more common at high levels of eccentricity. There was no relationship between axial force and lateral bending moment at injury which has been previously proposed as an injury criterion. These results provide the foundation for designing and evaluating strategies and devices for preventing severe spinal injuries.

Thresholds for the assessment of inflicted head injury by shaking trauma in infants: a systematic review.

In order to investigate potential causal relations between the shaking of infants and injuries, biomechanical studies compare brain and skull dynamic behavior during shaking to injury thresholds. However, performing shaking tolerance research on infants, either in vivo or ex vivo, is extremely difficult, if not impossible. Therefore, infant injury thresholds are usually estimated by scaling or extrapolating adult or animal data obtained from crash tests or whiplash experiments. However, it is doubtful whether such data accurately matches the biomechanics of shaking in an infant. Hence some thresholds may be inappropriate to be used for the assessment of inflicted head injury by shaking trauma in infants. A systematic literature review was conducted to 1) provide an overview of existing thresholds for head- and neck injuries related to violent shaking, and 2) to identify and discuss which thresholds have been used or could be used for the assessment of inflicted head injury by shaking trauma in infants. Key findings: The majority of studies establishing or proposing injury thresholds were found to be based on loading cycle durations and loading cycle repetitions that did not resemble those occurring during shaking, or had experimental conditions that were insufficiently documented in order to evaluate the applicability of such thresholds. Injury thresholds that were applied in studies aimed at assessing whether an injury could occur under certain shaking conditions were all based on experiments that did not properly replicate the loading characteristics of shaking. Somewhat validated threshold scaling methods only exist for scaling concussive injury thresholds from adult primate to adult human. Scaling methods that have been used for scaling other injuries, or for scaling adult injury thresholds to infants were not validated. There is a clear and urgent need for new injury thresholds established by accurately replicating the loading characteristics of shaking.

Biomechanical study of the thyroid cartilage: A model of bi-digital strangulation.

The presence of fracture on neck elements is an indication of violence. Both the hyoid bone and the larynx can be damaged by a strangulation mechanism. Thyroid cartilage, more specifically, may present lesions in response to this mechanical stress. These lesions result in fractures at the bases of the horns of the thyroid cartilage. This study focuses on the thyroid cartilage behavior in cases of bi-digital strangulation, using an anthropometric and biomechanical approach. To develop a biomechanical model, we performed an anthropometric study taking into account 14 distances measurements as well as 3 measurements of angles. These measures allowed us to determine a significant sexual dimorphism between individuals. Then, we define 6 morphologies models, composed of 3 females and 3 males individuals. In order to visualize the ossification of the cartilage, each model has been tested with bone properties. Strangulation cases were simulated by applying an imposed velocity of 0.4m/s then 1m/s. We observed different behaviors of the thyroid cartilage according to the sex and the morphology.

[Penetrating neck injury caused by stabbing: a rare but complex problem in the Netherlands]. / Penetrerend halsletsel door steekverwondingen.

Penetrating neck injuries (PNIs) as a result of stabbing or deliberate self-harm are complex and potentially life-threatening. Nowadays, selective non-operative management of PNI has become common practice. Diagnostic and treatment algorithms originating from high-volume trauma centres in South-Africa and North-America are used in Dutch clinical practice. Three patients that sustained a PNI are discussed. Two patients, aged 61 and 37, only had mild signs on physical examination that justified additional diagnostic investigations. In the first patient, a penetrating oesophageal injury was found and repaired. The latter had a partial Horner syndrome as a result of PNI, no underlying injuries were found. One patient, aged 57, was haemodynamically unstable and therefore received immediate surgical exploration of the neck. A penetrating injury of the jugular vein was discovered and repaired. A summary of literature and guidelines is presented for the benefit of Dutch physicians that may be confronted with these complex injuries.

Can the Neck Contribute to Persistent Symptoms Post Concussion? A Prospective Descriptive Case Series.

BACKGROUND: Persistent symptoms post concussion can arise from a range of sources, including the neck. There is little description of neck assessment findings in people with persistent symptoms post concussion. OBJECTIVES: To assess people with persistent symptoms following a concussion and determine whether the neck has also been injured, and to evaluate the potential of the neck to contribute to their symptoms. METHODS: A consecutive series of participants (n = 20) referred for neck assessment were prospectively recruited by 2 providers of a multidisciplinary concussion service for people with persistent symptoms. Data were collected at initial assessment and on completion of neck treatment, which included standard questionnaires (Rivermead Post Concussion Symptoms Questionnaire, Neck Disability Index, Dizziness Handicap Inventory); patient-reported measures of headache, dizziness, and neck pain; physical examination findings; and details of comorbidities. RESULTS: Participants were evaluated at a mean of 7.5 weeks post concussion (median, 5 weeks). On neck assessment, 90% were considered by the clinician to have a neck problem contributing to their current symptoms. Multiple findings were consistent with this view, including moderate-to-severe Neck Disability Index scores (mean ± SD, 33.4 ± 9.5 points), frequent neck pain (85%), frequent moderate-to-severe pain on occiput-C4 segmental assessment (85%), a positive flexion-rotation test (45%), and muscle tenderness (50%-55%). CONCLUSION: Multiple findings were indicative of concurrent neck injury, particularly involving the upper cervical spine. These neck-related findings are important to recognize, as they have the potential to contribute to persistent symptoms post concussion and may respond to neck treatment. This study was prospectively registered with the Australian New Zealand Clinical Trials Registry (ACTRN12616001183471). J Orthop Sports Phys Ther 2019;49(11):845-854. Epub 1 Jun 2019. doi:10.2519/jospt.2019.8547.

Width and neurophysiologic properties of tissue bridges predict recovery after cervical injury.

OBJECTIVE: To assess whether preserved dorsal and ventral midsagittal tissue bridges after traumatic cervical spinal cord injury (SCI) encode tract-specific electrophysiologic properties and are predictive of appropriate recovery. METHODS: In this longitudinal study, we retrospectively assessed MRI scans at 1 month after SCI that provided data on width and location (dorsal vs ventral) of midsagittal tissue bridges in 28 tetraplegic patients. Regression analysis assessed associations between midsagittal tissue bridges and motor- and sensory-specific electrophysiologic recordings and appropriate outcome measures at 12 months after SCI. RESULTS: Greater width of dorsal midsagittal tissue bridges at 1 month after SCI identified patients who were classified as being sensory incomplete at 12 months after SCI (p = 0.025), had shorter sensory evoked potential (SEP) latencies (r = -0.57, p = 0.016), and had greater SEP amplitudes (r = 0.61, p = 0.001). Greater width of dorsal tissue bridges predicted better light-touch score at 12 months (r = 0.40, p = 0.045) independently of baseline clinical score and ventral tissue bridges. Greater width of ventral midsagittal tissue bridges at 1 month identified patients who were classified as being motor incomplete at 12 months (p = 0.002), revealed shorter motor evoked potential (MEP) latencies (r = -0.54, p = 0.044), and had greater ratios of MEP amplitude to compound muscle action potential amplitude (r = 0.56, p = 0.005). Greater width of ventral tissue bridges predicted better lower extremity motor scores at 12 months (r = 0.41, p = 0.035) independently of baseline clinical score and dorsal tissue bridges. CONCLUSION: Midsagittal tissue bridges, detectable early after SCI, underwrite tract-specific electrophysiologic communication and are predictors of appropriate sensorimotor recovery. Neuroimaging biomarkers of midsagittal tissue bridges may be integrated into the diagnostic workup, prediction of recovery, and patients' stratification in clinical trials.

The influence of age on quality of life after upper body burn.

BACKGROUND: In Spain, the number of aged persons is increasing. By the year 2066, it is expected that 34.6% of the Spanish population will be over 65 years of age. Elderly people present a higher burning risk owing in part to impaired balance and decreased physical strength, lower cognitive abilities, or socioeconomic context. OBJECTIVE: Burns to the upper body body are common and affect both emotional state and physical function, thus leading to reduced quality of life (QoL). Our objective was to determine the influence of age on the QoL of patients who experienced burns to the upper body, with burns with 2 years. METHODS: This is an observational study with a sample of 58 patients with burns only on the upper body. Patients were divided into two groups: 29 patients of age over 65 years and 29 patients under 65 years; all of them attended the Vall d'Hebron Burn Center, Barcelona, between 2011 and 2014. From the original sample, 45 patients had survived by the time the information was gathered. The QoL of these individuals was evaluated with the Spanish version of the Burn Specific Health Scale. Demographic data (sex, age, total burn surface area [TBSA], burn mechanism, pathological history, length of hospital stay, and rehabilitation duration) were collected. Statistical analysis included parametric and nonparametric tests as appropriate with R3.3.3. RESULTS: There were no differences between groups regarding the mechanism of burn, TBSA, length of hospital stay, and the domains of QoL test. High blood pressure, diabetes, and other comorbidities were significantly more common in the elderly group than in the younger group. Eleven patients died in the elderly group and two in the younger group (p=0.012). CONCLUSION: As opposed to what could be expected, in this study, there were no significant differences between surviving patients in both age groups in terms of perceived QoL. Nevertheless, mortality after a burn in the upper side of the body was significantly higher in elderly people than in younger people. The present study results do not support the use of different rehabilitation approaches in elderly patients.

A New Neuropathologic Mechanism of Blood pH Irregularities After Neck Trauma: Importance of Carotid Body-Glossopharyngeal Nerve Network Degeneration.

OBJECTIVE: We created a neck trauma model by injecting blood into the sheath of rabbits' carotid bodies (CBs). Then we determined the relationship between neuronal degeneration of the CB due to hemorrhage of this organ and its clinical effects such as blood pH and heart rhythm. METHODS: The present study included 24 adult male New Zealand rabbits. The animals were divided into 3 groups: control (n = 5); sham (0.5 mL saline injected into CBs; n = 5); and study (CB trauma model; n = 14). pH values and heart rhythms were recorded before the experiment to determine the values under normal conditions, and measurements were repeated thrice in the days following the experiment. The number of normal and degenerated neuron density of CBs was counted. The relationship between the blood pH values, heart rhythms, and degenerated neuron densities was analyzed. RESULTS: Heart rhythms were 218 ± 20 in the control group, 197 ± 16 in the sham group (P = 0.09), and 167 ± 13 in the study group (P < 0.0005). pH values were 7.40 ± 0.041 in the control group, 7.321 ± 0.062 in the sham group (P = 0.203), and 7.23 ± 0.02 in study group (P < 0.0005). Degenerated neuron densities were 12 ± 4/mm3 in the control group, 430 ± 74/mm3 in the sham group (P < 0.005), and 7434 ± 810/mm3 in the study group (P < 0.0001). CONCLUSIONS: A high degenerate neuron density in the CB can decrease blood pH and hearth rhythm after neck trauma, and there might be a close relationship between the number of degenerated neurons and clinical findings (such as heart rhythm and blood pH). This relationship suggests that injury to the glossopharyngeal nerve-CB network can cause acidosis by disturbing the breathing-circulating reflex and results in respiratory acidosis.

Head and neck burns are associated with long-term patient-reported dissatisfaction with appearance: A Burn Model System National Database study.

INTRODUCTION: Burns affecting the head and neck (H&N) can lead to significant changes in appearance. It is postulated that such injuries have a negative impact on patients' social functioning, quality of life, physical health, and satisfaction with appearance, but there has been little investigation of these effects using patient reported outcome measures. This study evaluates the effect of H&N burns on long-term patient reported outcomes compared to patients who sustained burns to other areas. METHODS: Data from the National Institute on Disability, Independent Living, and Rehabilitation Research Burn Model System National Database collected between 1996 and 2015 were used to investigate differences in outcomes between those with and without H&N burns. Demographic and clinical characteristics for adult burn survivors with and without H&N burns were compared. The following patient-reported outcome measures, collected at 6, 12, and 24 months after injury, were examined: satisfaction with life (SWL), community integration questionnaire (CIQ), satisfaction with appearance (SWAP), short form-12 physical component score (SF-12 PCS), and short form-12 mental component score (SF-12 MCS). Mixed regression model analyses were used to examine the associations between H&N burns and each outcome measure, controlling for medical and demographic characteristics. RESULTS: A total of 697 adults (373 with H&N burns; 324 without H&N burns) were included in the analyses. Over 75% of H&N injuries resulted from a fire/flame burn and those with H&N burns had significantly larger burn size (p<0.001). In the mixed model regression analyses, SWAP and SF-12 MCS were significantly worse for adults with H&N burns compared to those with non-H&N burns (p<0.01). There were no significant differences between SWL, CIQ, and SF-12 PCS. CONCLUSIONS: Survivors with H&N burns demonstrated community integration, physical health, and satisfaction with life outcomes similar to those of survivors with non-H&N burns. Scores in these domains improved over time. However, survivors with H&N burns demonstrated worse satisfaction with their appearance. These results suggest that strategies to address satisfaction with appearance, such as reconstructive surgery, cognitive behavior therapy, and social skills training, are an area of need for survivors with H&N burns.

On the relative importance of bending and compression in cervical spine bilateral facet dislocation.

BACKGROUND: Cervical bilateral facet dislocations are among the most devastating spine injuries in terms of likelihood of severe neurological sequelae. More than half of patients with tetraparesis had sustained some form of bilateral facet fracture dislocation. They can occur at any level of the sub-axial cervical spine, but predominate between C5 and C7. The mechanism of these injuries has long been thought to be forceful flexion of the chin towards the chest. This "hyperflexion" hypothesis comports well with intuition and it has become dogma in the clinical literature. However, biomechanical studies of the human cervical spine have had little success in producing this clinically common and devastating injury in a flexion mode of loading. METHODS: The purpose of this manuscript is to review the clinical and engineering literature on the biomechanics of bilateral facet dislocations and to describe the mechanical reasons for the causal role of compression, and the limited role of head flexion, in producing bilateral facet dislocations. FINDINGS: Bilateral facet dislocations have only been produced in experiments where compression is the primary loading mode. To date, no biomechanical study has produced bilateral facet dislocations in a whole spine by bending. Yet the notion that it is primarily a hyper-flexion injury persists in the clinical literature. INTERPRETATION: Compression and compressive buckling are the primary causes of bilateral facet dislocations. It is important to stop using the hyper-flexion nomenclature to describe this class of cervical spines injuries because it may have a detrimental effect on designs for injury prevention.