5-14. MECHANISM OF INJURY

Spinal cord injury can be caused by a number of mechanisms. Mechanisms of injury discussed here are divided into these four areas: axial loading; flexion, extension, and rotation; lateral bending; and distraction.

a. Axial Loading.

(1) Definition. Axial loading is a sudden, excessive compression which drives the weight of the body against the head. For example, a downward blow to the head such as a heavy object falling on the head can crush or fracture the vertebrae, which in turn can pinch or compress the spinal cord or nerve roots. An upward force to the feet as in a fall from a great height can have the same result.

(2) Injuries. In either of the instances mentioned in the previous paragraph, the sudden excessive compression drives the weight of the head and thorax against the lumbar spine while the sacral spine is driven upward. Driving injuries often cause axial loading injury.

b. Flexion, Extension, Rotation.

(1) Definition. Flexion is the act of bending or the condition of being bent. Extension is movement by which the two elements of any jointed part are drawn away from each other. Rotation is movement of the body about the body's axis. These spinal cord injuries occur when the spine moves past its normal range of motion.

(2) Injuries. Injuries caused include bone damage, tearing of muscles and ligaments, and tearing of the spinal cord.

(a) Flexion-rotation injuries. These injuries can occur at any level of the spinal cord. Usually, flexion-rotation injuries involve the cervical area, particularly C5 and C6. The cervical vertebrae can be dislocated by a sudden impact, the impact shearing supporting ligaments and blood vessels.

(b) Forced extension (hyperextension) injuries. In this injury, the head is sharply thrust back, and the upper spinal segments hyperextend (that is, these segments are extended beyond their normal limits). Such an accident can disrupt support ligaments, rupture intervertebral disks, and fracture one or more pedicles (vertebrae stem). The result is that the spinal cord is compressed and destabilized. An example is a person falling face down on stairs he is climbing up. The force to the head or chin thrusts the head back sharply, intervertebral disks rupture, vertebral bodies fracture, and supporting ligaments are damaged.

c. Lateral Bending.

(1) Definition. The head and neck are bent to one side, beyond normal limits.

(2) Injury. Lateral bending can cause significant injury to the cervical spine.

d. Distraction.

(1) Definition. Distraction is the pulling apart of the spine.

(2) Injury. This pulling apart stretches and tears the spinal cord. An example of distraction as a mechanism of injury is suicide by hanging. Gunshot wounds to the chest, back, and abdomen may also cause distraction type injury to the spinal cord.

CAUTION: It is wise to assume that any patient who is unconscious after trauma might have spinal cord injury. Also, assume that any patient with head trauma injury may have a spinal cord injury until you know otherwise.