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Minor injuries of the cervical spine are essentially defined as injuries that do not involve a fracture. Archetypical of minor cervical injury is the whiplash injury. Among other reasons, neck pain after whiplash has been controversial because critics do not credit that an injury to the neck can occur in a whiplash accident. In pursuit of the injury mechanism, bioengineers have used mathematical modelling, cadaver studies, and human volunteers to study the kinematics of the neck under the conditions of whiplash. Particularly illuminating have been cinephotographic and cineradiographic studies of cadavers and of normal volunteers. They demonstrate that externally, the head and neck do not exceed normal physiological limits. However, the cervical spine undergoes a sigmoid deformation very early after impact. During this deformation, lower cervical segments undergo posterior rotation around an abnormally high axis of rotation, resulting in abnormal separation of the anterior elements of the cervical spine, and impaction of the zygapophysial joints. The demonstration of a mechanism for injury of the zygapophysial joints complements postmortem studies that reveal lesions in these joints, and clinical studies that have demonstrated that zygapophysial joint pain is the single most common basis for chronic neck pain after injury.

Unlabelled: This review constitutes the first of four reviews that systematically address contemporary knowledge about the mechanical behavior of the cervical vertebrae and the soft-tissues of the cervical spine, under normal conditions and under conditions that result in minor or major injuries. This first review considers the normal kinematics of the cervical spine, which predicates the appreciation of the biomechanics of cervical spine injury. It summarizes the cardinal anatomical features of the cervical spine that determine how the cervical vertebrae and their joints behave. The results are collated of multiple studies that have measured the range of motion of individual joints of the cervical spine. However, modern studies are highlighted that reveal that, even under normal conditions, range of motion is not consistent either in time or according to the direction of motion. As well, detailed studies are summarized that reveal the order of movement of individual vertebrae as the cervical spine flexes or extends. The review concludes with an account of the location of instantaneous centres of rotation and their biological basis., Relevance: The fact and precepts covered in this review underlie many observations that are critical to comprehending how the cervical spine behaves under adverse conditions, and how it might be injured. Forthcoming reviews draw on this information to explain how injuries might occur in situations where hitherto it was believed that no injury was possible, or that no evidence of injury could be detected.

OBJECTIVE: To determine the morphology of the latissimus dorsi in order to assess its actions on the shoulder, the lumbar spine and the sacroiliac joint. DESIGN: A dissection study accompanied by an analysis of the force vectors of the muscle and its parts. BACKGROUND: Although recognised as a muscle of the shoulder, latissimus dorsi has been accorded a role as an extensor of the lumbar spine, and is said to brace the sacroiliac joint. Consideration of the anatomy of the latissimus dorsi suggests that the magnitude of these actions has been overstated. METHODS: The fascicular anatomy of the latissimus dorsi was determined by dissection in five adult cadavers. The size, attachments, and orientation of each fascicle were determined. By applying a force coefficient the maximum force of each fascicle was estimated from its physiological cross-sectional area. By summing the forces and moments of each fascicle the maximum force exerted by latissimus dorsi was calculated for its actions on the shoulder, the lumbar spine, and the sacroiliac joint. RESULTS: The latissimus dorsi was found to consist of a series of fascicles with segmental attachments to the lower six thoracic spinous processes, the L1 and L2 spinous processes, the lateral raphe of the thoracolumbar fascia, the iliac crest and the lower three ribs. These fascicles were uniform in size across a given muscle but varied from specimen to specimen. The maximum total force exerted by the latissimus dorsi on the shoulder was estimated to range between 162 and 529 N, but in view of the attachments of the muscle, only a portion of that force can be exerted on the lumbar spine. The maximum extensor moment exerted on the lumbar spine was calculated to be 6.3 N m. The maximum force exerted across the sacroiliac joint was calculated to be 30 N. CONCLUSIONS: The latissimus dorsi is designed to move the upper limb or to raise the entire trunk in brachiation. Its possible contribution to extension of the lumbar spine is trivial as is its capacity to brace the sacroiliac joint. RELEVANCE: Despite assertions and concerns to the contrary, the latissimus dorsi is of little mechanical importance in the lumbosacral region.

The relationship was examined between the height and slope of the cervical zygapophyseal joints and the patterns of motion of the cervical vertebrae. The height and orientation of the C3C7 superior articular processes were measured in lateral radiographs of 40 normal subjects. The C4-C6 facets were oriented at approximately 40° to the vertical, while the C3 and C7 facets were more steeply oriented. The heights of the superior articular processes were found to increase at progressively lower vertebral levels. Contrary to published views, the slope of the superior articular facets has no bearing on the pattern of motion of the cervical vertebrae. No relationship was found between slope of the facets and the location of the instantaneous axes of rotation of the cervical vertebrae. In contrast the height of the articular processes was perfectly related to the location of the axes of rotation. Articular height, but not slope, is a major determinant of the patterns of motions of the cervical vertebrae. This study provides data necessary to confirm or deny the putative roles of the cervical zygapophyseal joints in determining motion of the cervical spine in the sagittal plane., (Copyright © 1994. Published by Elsevier Ltd.)

Dissection studies revealed the fascicular anatomy of the trapezius. Its occipital and nuchal fibres passed downwards but mainly transversely to insert into the clavicle. Fibres from C7 and T1 passed transversely to reach the acromion and spine of the scapula. Its thoracic fibres converged to the deltoid tubercle of the scapula. Volumetric studies demonstrated that the fibres from C7, T1, and the lower half of ligamentum nuchae were the largest. The essentially transverse orientation of the upper and middle fibres of trapezius precludes any action as elevators of the scapula as commonly depicted. Rather the action of these fibres is to draw the scapula and clavicle backwards or to raise the scapula by rotating the clavicle about the sternoclavicular joint. By balancing moments the trapezius relieves the cervical spine of compression loads., (Copyright © 1994. Published by Elsevier Ltd.)

The fascicular anatomy of the psoas major was determined by dissection in three cadavers. Its actions on the lumbar spine in the sagittal plane were modelled on erect, flexion, and extension radiographs of ten adult males. Calculations revealed that psoas exerts only very small moments that tend to extend the upper lumbar spine and to flex the lower lumbar spine, but at maximum contraction the psoas exerts severe compression forces on the lumbar segments, and large shear forces., (Copyright © 1992. Published by Elsevier Ltd.)

The locations of the instantaneous axes of rotation for the cervical motion segments C2-3 to C6-7 were determined from flexion-extension radiographs of 40 normal subjects using a modified overlay technique. The biological variation of the instantaneous axes of rotation was small, as was the technical error associated with the technique used. The data obtained enabled the formal definition of the normal range of locations for the instantaneous axes of rotation of the typical cervical motion segments., (Copyright © 1991. Published by Elsevier Ltd.)

The reliability of a modified protocol for plotting the instantaneous axes of sagittal rotation for the cervical spine was evaluated by measuring the observer differences when the process was performed separately by two observers, and by a single observer, on two separate occasions. Small observer differences were found both for individual steps in the process and for the process as a whole. These differences were substantially less than those found using the conventional technique for plotting the instantaneous axes of rotation. The improvement in the technique was resultant from the use of stricter criteria for recognizing and tracing vertebral landmarks., (Copyright © 1991. Published by Elsevier Ltd.)

The reliability of the conventional technique for determining the instantaneous axes of rotation of the cervical motion segments was evaluated by comparing the determinations made by two observers and the same observer on two separate occasions. Different observers found the same mean location for the instantaneous axis at each segment in a test population of 17 normal subjects, but for any given subject the interobserver and intraobserver differences were large, with a relative variation of up to 35%. Thus, while reliable for determining the mean location of the instantaneous axis of rotation in a population, the technique was not reliable for determining the axis in a given subject. Qualitative analysis suggested that the identification of the radiographic images of the vertebrae and their tracing is the greatest source of error for this technique., (Copyright © 1991. Published by Elsevier Ltd.)

Whereas the symptoms of whiplash injury are frequently poorly understood or misrepresented as due to neurosis, a review of the literature reveals a considerable amount of biomechanical and experimental data that substantiate a diverse organic basis for these symptoms, including disorders commonly not considered or sought for in the investigation of whiplash. Moreover, formal studies fail to substantiate the notion of 'litigation neurosis' being the cause of prolonged symptoms. This review synthesises the anatomy and pathology of whiplash, and the pathophysiology of symptoms, into what can be construed as the organic basis for whiplash., (Copyright © 1986. Published by Elsevier Ltd.)

Dissection studies revealed that the fibres of the lumbar multifidus are divided by distinct cleavage planes into five bands. Each band arises from a lumbar spinous process, and is innervated unisegmentally. The lumbar multifidus is therefore composed of five myotomes arranged such that the fibres that move a particular segment are innervated by the nerve of that segment. Target points are described that enable electromyography to be performed on paraspinal muscles of known unisegmental innervation., (Copyright © 1986. Published by Elsevier Ltd.)

The possible actions of the lumbar multifidus were determined by plotting the points of attachment and orientation of each of its component fascicles on radiographs of 5 cadavers and 21 living subjects. Subsequent analysis revealed that the principal action of multifidus is posterior sagittal rotation (extension without posterior translation) of the lumbar vertebrae. It has no translatory action. Any axial rotation exerted by the lumbar multifidus is only a minor, secondary action which must be coupled with posterior sagittal rotation. This extension balances the flexion moment generated by the abdominal muscles which rotate the trunk. The constancy of the sites of attachment of the multifidus allows each of its fascicles to be plotted accurately on radiographs or computer diagrams which can be used to produce highly detailed analyses or models of the forces exerted by the multifidus on the lumbar spine., (Copyright © 1986. Published by Elsevier Ltd.)

The back muscles alone are unable to provide the extensor moment required to lift large weights, and must be aided by another source of anti-flexion moments. It has been postulated that contraction of the abdominal muscles can provide an extension moment by developing tension in the thoracolumbar fascia (TLF). Anatomical studies and a biomechanical analysis, however, reveal that the anti-flexion moment generated in this way is only very small. Too little of the abdominal musculature attaches to the TLF to generate a significant tension in it. Previous calculations of the forces in the TLF have overestimated the tension developed in it because of erroneous assumptions and interpretations of the relevant anatomy. Whatever the role played by the TLF in lifting it must be essentially independent of abdominal mechanisms., (Copyright © 1987. Published by Elsevier Ltd.)