This section is from the book "Applied Anatomy: The Construction Of The Human Body", by Gwilym G. Davis. Also available from Amazon: Applied anatomy: The construction of the human body.
The vertebras may be dislocated and fractured.
Dislocation is rarer than fracture; it is most common in the cervical region. The cervical vertebras have their articular facets sloping downward and backward, hence dislocation occurs when the upper vertebras are pushed in front of the lower.
Fig. 484. - Lateral view, showing relation of transverse process of atlas to tip of mastoid process.
The cervical spine normally has but slight rotation, hence when luxated one articular surface is rotated or pushed over and in front of the one below, the opposite articular surface acting as the axis and the distance between the two articulations as the radius of the arch in which the luxated parts move. The elevation of the luxated articular process over the one below is favored by the bending of the spine above toward the opposite side. The head is rotated and inclined toward the uninjured side. Bilateral luxation is rare without associated fracture. It is produced by anterior flexion, and the head and neck are inclined forward while the lower vertebra of the dislocated joints inclines backward, producing a kyphotic condition.
Luxation affects most often the fourth, fifth, and sixth cervical vertebras. The atlas may be dislocated forward or backward by rupture of the transverse ligament, fracture of the odontoid process, or by a slipping of the process under the ligament.
Luxation of the atlas laterally is very rare, owing to there being normally a total rotation of 60 degrees.
To reduce the luxation an anaesthetic is given to relax the muscles, and cautious extension is made and the head gently rotated.
Fracture of the spine is frequently associated with luxation. It is most frequent low down in the cervical region and at the junction of the dorsal and lumbar vertebrae, these being the places where the more fixed dorsal portion passes into the more movable cervical and lumbar portions (Fig. 485). The vertebrae are supported at three points - the bodies and the two articular processes. The spinous and articular processes are rarely fractured alone; they may be broken, however, by direct violence. The laminae on each side of the articular processes may be broken and the detached part with the spinous process may be pushed inward, injuring the cord. Fracture of the bodies is most frequent and is due to anterior flexion. The bodies and intervertebral disks are compressed, crushed, and torn. This is accompanied by either luxation or fracture of the articular processes, and occurs most often in the region of the lower dorsal vertebrae. Injury to the cord is common. The parts are not often fixed in a markedly displaced position, as is the case with luxations of the neck, hence attempts at reduction are rarely necessary and fixation is to be aimed for in treatment. The site of injury is determined not only by an examination of the spinous processes but also by the extent of interference with the functions of the cord (see page 483).