Comparative strengths and structural properties of the upper and lower cervical spine in flexion and extension

The purpose of this study is to test the hypothesis that the upper cervical spine is weaker than the lower cervical spine in pure flexion and extension bending, which may explain the propensity for upper cervical spine injuries in airbag deployments. An additional objective is to evaluate the relative strength and flexibility of the upper and lower cervical spine in an effort to better understand injury mechanisms, and to provide quantitative data on bending responses and failure modes. Pure moment flexibility and failure testing was conducted on 52 female spinal segments in a pure-moment test frame. The average moment at failure for the O-C2 segments was 23.7+/-3.4Nm for flexion and 43.3+/-9.3Nm for extension. The ligamentous upper cervical spine was significantly stronger in extension than in flexion (p=0.001). The upper cervical spine was significantly stronger than the lower cervical spine in extension. The relatively high strength of the upper cervical spine in tension and in extension is paradoxical given the large number of upper cervical spine injuries in out-of-position airbag deployments. This discrepancy is most likely due to load sharing by the active musculature.     

The cervical locking mechanism. Its contribution to the cervical spine stability and to the vertebral artery and spinal cord safety. An anatomical study.

Investigations were conducted with macerated cervical vertebrae and human cadavers. During extension, lateral flexion, and rotation of the neck, the cervical transverse process engages to the top of the upper articular process of the subjacent vertebra, thus embodying the locking mechanism which plays an important role in the stabilization of the cervical spine and the protection of the integrity of vertebral arteries, spinal cord, and nerve roots. A deficiency of this locking mechanism may cause a vertebrobasilar insufficiency or a cervical myelopathy.     

Differential scaling patterns of vertebrae and the evolution of neck length in mammals

Almost all mammals have seven vertebrae in their cervical spines. This consistency represents one of the most prominent examples of morphological stasis in vertebrae evolution. Hence, the requirements associated with evolutionary modifications of neck length have to be met with a fixed number of vertebrae. It has not been clear whether body size influences the overall length of the cervical spine and its inner organization (i.e., if the mammalian neck is subject to allometry). Here, we provide the first large‐scale analysis of the scaling patterns of the cervical spine and its constituting cervical vertebrae. Our findings reveal that the opposite allometric scaling of C1 and C2–C7 accommodate the increase of neck bending moment with body size. The internal organization of the neck skeleton exhibits surprisingly uniformity in the vast majority of mammals. Deviations from this general pattern only occur under extreme loading regimes associated with particular functional and allometric demands. Our results indicate that the main source of variation in the mammalian neck stems from the disparity of overall cervical spine length. The mammalian neck reveals how evolutionary disparity manifests itself in a structure that is otherwise highly restricted by meristic constraints.     

PATIENTS WITH MULTIPLE INJURIES—Management in Office Practice

In the emergency treatment of a patient with multiple severe injuries who is brought to a physician''s office from the scene of an accident, the physician must make sure that a way for air to reach the lungs is open, must treat or prevent shock, stop hemorrhage and apply temporary splints to fractures of the extremity.The possibility that the tip of the tongue is blocking the pharynx and that blood or other fluid is clogging the airway must be considered. Fluids should be administered intravenously to prevent shock and gauze pads should be held firmly in place to control bleeding.     

Does the correlation between schmorl's nodes and vertebral morphology extend into the lumbar spine?

Schmorl's nodes are depressions on vertebrae due to herniation of the nucleus pulposus of the intervertebral disc into the vertebral body. This study provides an extension of our previous study which analyzed the shape of the lower thoracic spine and found that vertebral morphology was associated with the presence of Schmorl's nodes. Ninety adult individuals from the late Medieval site of Fishergate House, York, and the Post‐Medieval site of Coach Lane, North Shields, Tyne and Wear, England, were analysed using 2D geometric morphometrics to identify possible relationships between vertebral morphology and Schmorl's nodes at the thoraco‐lumbar junction and in the lumbar spine. A significant correlation was found between vertebral shape and the presence of Schmorl's nodes in the twelfth thoracic vertebrae and the first to third lumbar vertebrae. The findings corroborate previous studies and suggest that vertebral shape may be an important factor in spinal health. It is hypothesized that the pedicle shape of affected vertebrae may not provide adequate structural support for the vertebral bodies, resulting in vertical disc herniation. Am J Phys Anthropol 157:526–534, 2015. © 2015 Wiley Periodicals, Inc.     

The extent of lead fragmentation observed in deer culled by sharpshooting

Sharpshooting is a proven management technique to lower white-tailed deer (Odocoileus virginianus) densities in areas where hunting is precluded. A donation program that allows for the consumptive use of these culled deer is often necessary to gain public approval for such a program. We culled 40 deer in Indiana using sharpshooting methods (head and neck shot placement) and radiographed the carcasses to determine if lead fragmentation spread throughout the skeletal muscle system. In 30 deer where shot placement was between the cranium and fourth cervical vertebrae, we observed no lead fragments in any thoracic or crural muscle tissue. Of 10 deer where shot placement was between the fifth and seventh cervical vertebrae, 8 deer experienced lead fragments in the extensor spinae muscle. Deer culled with highly frangible bullets via sharpshooting in the cranium or upper cervical spine have minimal risk of experiencing lead fragmentation in the thoracic or crural muscle systems. Deer shot in the lower neck may experience lead fragmentation in the anterior extensor spinae muscle, and up to 40 cm of that muscle should be removed before consumption. © 2011 The Wildlife Society.     

Cervical spine posteroanterior stiffness differs with neck position

PurposeSpinal stiffness is commonly considered when treating patients with neck pain, but there are few studies reporting the objective measurement of cervical spine stiffness or the possible kinesiological factors that may affect its quantification. The aim of this study was to determine if the position of the neck affects cervical spine stiffness.MethodsAn instrumented stiffness assessment device measured posteroanterior cervical spine stiffness at C4 of 25 prone-lying asymptomatic subjects in three neck positions in randomised order: maximal flexion, maximal extension, and neutral. The device applied five standardised mechanical oscillatory pressures while measuring the applied force and concurrent displacement, defining stiffness as the slope of the linear portion of the force–displacement curve. Repeated measures analysis of variance with Bonferroni-adjusted post hoc comparisons determined whether stiffness differed between neck positions.ResultsThere was a significant difference in cervical spine stiffness between different neck positions (F_(1.6,38.0) = 16.6, P < 0.001). Stiffness was least in extension with a mean of 3.09 N/mm (95% CI 2.59, 3.58) followed by neutral (3.94, 95% CI 3.49, 4.39), and then flexion (4.32, 95% CI 3.96, 4.69).ConclusionWhen assessing cervical spine stiffness, neck position should be standardised to ensure maximal reliability and utility of stiffness judgments.     

A biomechanical model for the analysis of the cervical spine in static postures.

To gain a better understanding of the forces working on the cervical spine, a spatial biomechanical computer model was developed. The first part of our research was concerned with the development of a kinematic model to establish the axes of rotation and the mutual position of the head and vertebrae with regard to flexion, extension, lateroflexion and torsion. The next step was the introduction of lines of action of muscle forces and an external load, created by gravity and accelerations in different directions, working on the centre of gravity of the head and possibly a helmet. Although the results of our calculations should be interpreted cautiously in the present stage of our research, some conclusions can be drawn with respect to different head positions. During flexion muscle forces and joint reaction forces increase, except the force between the odontoid and the ligamentum transversum atlantis. This force shows a minimum during moderate flexion. The joint reaction forces on the levels C0-C1, C1-C2, and C7-T1 reach minimum values during extension, each in different stages of extension. Axial rotation less than 35 degrees does not need great muscle forces, axial rotation further than 35 degrees causes muscle forces and joint reaction forces to increase fast. While performing, lateral flexion muscle forces and joint reaction forces must increase rapidly to balance the head. We obtained some indications that the order of magnitude of the calculated forces is correct.     

Severe upper airway obstruction due to delayed retropharyngeal hematoma formation following blunt cervical trauma

Background

We report a case of severe upper airway obstruction due to a retropharyngeal hematoma that presented nearly one day after a precipitating traumatic injury. Retropharyngeal hematomas are rare, but may cause life-threatening airway compromise.

Case presentation

A 50 year-old man developed severe dyspnea with oropharyngeal airway compression due to retropharyngeal hematoma 20 hours after presenting to the emergency department. The patient also had a fractured first cervical vertebra and was diagnosed with a left brachial plexopathy. The patient underwent emergent awake fiberoptic endotracheal intubation to provide a definitive airway.

Conclusion

Retropharyngeal hematoma with life-threatening airway compromise can develop hours or days after a precipitating injury. Clinicians should be alert to the potential for this delayed airway collapse, and should also be prepared to rapidly secure the airway in this patient population likely to have concomitant cervical spinal or head injuries.     

Comparison of Cervical Spine Anatomy in Calves,Pigs and Humans

Background Context

Animals are commonly used to model the human spine for in vitro and in vivo experiments. Many studies have investigated similarities and differences between animals and humans in the lumbar and thoracic vertebrae. However, a quantitative anatomic comparison of calf, pig, and human cervical spines has not been reported.

Purpose

To compare fundamental structural similarities and differences in vertebral bodies from the cervical spines of commonly used experimental animal models and humans.

Study Design

Anatomical morphometric analysis was performed on cervical vertebra specimens harvested from humans and two common large animals (i.e., calves and pigs).

Methods

Multiple morphometric parameters were directly measured from cervical spine specimens of twelve pigs, twelve calves and twelve human adult cadavers. The following anatomical parameters were measured: vertebral body width (VBW), vertebral body depth (VBD), vertebral body height (VBH), spinal canal width (SCW), spinal canal depth (SCD), pedicle width (PW), pedicle depth (PD), pedicle inclination (PI), dens width (DW), dens depth (DD), total vertebral width (TVW), and total vertebral depth (TVD).

Results

The atlantoaxial (C1–2) joint in pigs is similar to that in humans and could serve as a human substitute. The pig cervical spine is highly similar to the human cervical spine, except for two large transverse processes in the anterior regions ofC4–C6. The width and depth of the calf odontoid process were larger than those in humans. VBW and VBD of calf cervical vertebrae were larger than those in humans, but the spinal canal was smaller. Calf C7 was relatively similar to human C7, thus, it may be a good substitute.

Conclusion

Pig cervical vertebrae were more suitable human substitutions than calf cervical vertebrae, especially with respect to C1, C2, and C7. The biomechanical properties of nerve vascular anatomy and various segment functions in pig and calf cervical vertebrae must be considered when selecting an animal model for research on the spine.     

Effect of muscle wrapping on model estimates of neck muscle strength

Of the computational models of the cervical spine reported in the literature, not one takes into account the changes in muscle paths due to the underlying vertebrae. Instead, all model the individual muscle paths as straight-line segments. The major aim of this study was to quantify the changes in muscle moment arm, muscle force and joint moment due to muscle wrapping in the cervical spine. Five muscles in a straight-line model of the cervical spine were wrapped around underlying vertebrae, and the results obtained from this model were compared against the original. The two models were then validated against experimental and computational data. Results show that muscle wrapping has a significant effect on muscle moment arms and therefore joint moments and should not be neglected.     

Effect of muscle wrapping on model estimates of neck muscle strength

Of the computational models of the cervical spine reported in the literature, not one takes into account the changes in muscle paths due to the underlying vertebrae. Instead, all model the individual muscle paths as straight-line segments. The major aim of this study was to quantify the changes in muscle moment arm, muscle force and joint moment due to muscle wrapping in the cervical spine. Five muscles in a straight-line model of the cervical spine were wrapped around underlying vertebrae, and the results obtained from this model were compared against the original. The two models were then validated against experimental and computational data. Results show that muscle wrapping has a significant effect on muscle moment arms and therefore joint moments and should not be neglected.     

Increases of calcium and magnesium and decrease of iron in human posterior longitudinal ligaments of the cervical spine with aging

To elucidate compositional changes of ligaments with aging, the authors investigated age-related changes of elements in the posterior longitudinal ligaments (PLLs) by inductively coupled plasma—atomic emission spectrometry. After the ordinary dissection, PLLs were resected from the subjects ranging in age from 65 to 95 yr. The PLLs of the cervical spine were resected between the fourth and fifth cervical vertebrae, the PLLs of the thoracic spine between the fifth and seventh thoracic vertebrae, and the PLLs of the lumbar spine between the second and third lumbar vertebrae. Calcium and magnesium increased progressively with aging in the PLLs of the cervical spine, but they did not increase with aging in the PLLs of the thoracic and lumbar spine. In contrast, iron decreased gradually with aging in the PLLs of the cervical spine. Regarding the relationships among elements, significant correlations were found among the contents of calcium, phosphorus, magnesium, and sodium in the PLLs of the cervical spine.     

The Hammer and the Eye: Beware

In reporting this small series of foreign-body injuries to the eye it is emphasized how normal an eye may appear and yet have a foreign body lurking in its anterior chamber. The patient''s account of the injury may be very deceptive and an x-ray picture of the eye must be taken if a foreign body is even remotely suspected, particularly if a hammer is mentioned. Prompt diagnosis followed by well executed surgery leads to good results in these cases.     

The neutral posture of the cervical spine is not unique in human subjects

Cervical spine injuries often happen in dynamic environments (e.g., sports and motor vehicle crashes) where individuals may be moving their head and neck immediately prior to impact. This motion may reposition the cervical vertebrae in a way that is dissimilar to the upright resting posture that is often used as the initial position in cadaveric studies of catastrophic neck injury. Therefore our aim was to compare the “neutral” cervical alignment measured using fluoroscopy of 11 human subjects while resting in a neutral posture and as their neck passed through neutral during the four combinations of active flexion and extension movements in both an upright and inverted posture. Muscle activation patterns were also measured unilaterally using surface and indwelling electromyography in 8 muscles and then compared between the different conditions. Overall, the head posture, cervical spine alignment and muscle activation levels were significantly different while moving compared to resting upright. Compared to the resting upright condition, average head postures were 6–13° more extended, average vertebral angles varied from 11° more extended to 10° more flexed, and average muscle activation levels varied from unchanged to 10% MVC more active, although the exact differences varied with both direction of motion and orientation. These findings are important for ex vivo testing where the head and neck are statically positioned prior to impact – often in an upright neutral posture with negligible muscle forces – and suggest that current cadaveric head-first impact tests may not reflect many dynamic injury environments.     

Cervical spine injuries in rugby players.

Nine patients with serious cervical spine injuries that occurred while they were playing rugby were seen in a British Columbia acute spinal cord injury unit during the period 1975-82. All the injuries had occurred during the "scrum" or the "tackle". Two of the patients were rendered permanently quadriplegic, and one patient died. There is a need for a central registry that would record all cervical spine injuries in rugby players as well as for changes in the rules of the game.     

Examining motion in the cervical spine I: imaging systems and measurement techniques

Instruments for measuring mobility in the cervical spine range from plumb-lines and inclinometers to sophisticated optoelectronic systems. In order to investigate the need and possible uses for an enhancement to a new diagnostic instrument, we examine some of the available diagnostic systems suitable for cervical motion analysis. These should be of practical use in a clinical setting for the diagnosis of soft tissue injuries. We begin by evaluating the respective roles of plain radiographs, cineradiography, computer tomography, and magnetic resonance imaging in examining the cervical spine. Then we consider Moiré photography, inclinometers, and some opto-electronic scanners, as well as the mathematical techniques needed to correlate skin and spine motion with these devices. We find that there does not appear to be an effective non-invasive tool for comprehensive clinical cervical motion analysis; in particular, coupled joint motion is inadequately quantified. Improperly diagnosed cervical spine injuries, such as hyperextension and hyperflexion, may result in chronic long-term effects. Therefore, instrumentation that would permit objective, routine clinical evaluation of patients could help to avoid such situations.     

Laryngeal Trauma

Laryngeal trauma may be obscured by associated injuries of the face and chest. An early assessment of these injuries should be made. Many cases may require observation only. In patients with severe laryngeal fractures, preservation of the airway and control of hemorrhage must first be assured. Following this, splinting by external or internal means should be carried out. Three severe laryngeal injuries were splinted with open and closed plastic moulds, with satisfactory results. It is proposed that early recognition and proper management of severe cases of this nature would shorten the treatment and achieve the best results.     

CINERADIOGRAPHIC STUDIES OF THE NORMAL CERVICAL SPINE

By considering the cervical spine as several segments with relatively different motions, an understanding of the total possible motions of the cervical spine can be more easily attained.Reversal of the cervical lordosis is a normal part of the flexion action and can result from positioning of the patient for radiographic studies.The effect of standing or sitting postures, and methods of initiating flexion of the neck should be considered in the evaluation of routine flexion and extension studies.Evaluation of individual cervical segments may be accomplished by the use of different methods of initiating flexion.