Traumatology

Etiologies and Types of Spinal Injury, and the		Isolated Traumatic Disk Rupture	60
Role of Pre-existing Degenerative Changes	59	Vertebral Body Fracture with Injury of the
Sprains of the Motion Segment	60	Intervertebral Disk	62

Etiologies and Types of Spinal Injury, and the Role of Pre-existing Degenerative Changes

The intervertebral disks, like the other components of the spinal motion segments, are only rarely subject to direct trauma. The spine is an axial organ located in a central position within the body and protected on all sides by soft tissue, so that direct blunt or penetrating trauma rarely affects it. The frequently made diagnosis of “spinal contusion” is probably only rarely correct.

Etiology. Spinal trauma is usually due to an indirect influence such as spraining, bending, or twisting. The segmental construction of the spine, with alternating solid and elastic components, renders it relatively resistant to injury by most types of applied external forces. Spinal trauma is nonetheless commonly encountered in clinical practice, usually as the result of axial compression, e.g., after a fall from a great height, or of sudden bending, with compression on the concave side and distraction on the convex side. There is often a torsional component as well. Trauma of the motion segment can involve the intervertebral disk in a number of different ways, as will be explained.

Types of injury. Trauma of the intervertebral disk can be classified into the following major categories:

sprains of the motion segment

disk tears

vertebral body fractures with disk involvement.

The most commonly traumatized motion segments are those located at the zones of transition between relatively fixed and relatively mobile regions of the spine, i.e., the atlanto-occipital and atlantoaxial segments, the lower segments of the cervical and lumbar regions, and the thoracolumbar junction. An important aspect of disk trauma and of spinal trauma in general, in all regions of the spine, is that the traumatic deformation and its accompanying pathological features (edema, hematoma) often lies in the immediate vicinity of the spinal cord and its nerve roots, which may be affected by the injury either directly or indirectly. Unlike most injuries elsewhere in the musculoskeletal system, traumatic disturbances of the structure and function of the spine are commonly associated with neurological dysfunction.

The role of pre-existing degenerative changes. The severity of a traumatic disk injury depends not only on the magnitude and direction of the externally applied force, but also on the state of the disk just before it is injured. We have shown experimentally that a healthy intervertebral disk cannot be injured by an externally applied force of practically any kind, unless the vertebral body is fractured first. Similar findings have often been reported in the literature (Göcke 1932, Lob 1951, Ingelmark and Ekholm 1952, Wyss and Ulrich 1953, Hirsch 1954, Güntz 1958, Plaue et al. 1974, Adams and Hutton 1984, Eysel and Fürderer 2004). Motion segments with pre-existing degenerative changes will, however, behave differently. Here, a relatively light loading of the anterior half of the motion segment may suffice to cause posterior displacement of disk tissue beyond the boundary of the disk. Because the ligaments between the vertebral bodies are also relatively weak in individuals with disk degeneration, such individuals are also more susceptible to traumatic slippage of the vertebrae. Hinz (1970) showed that, in acceleration–deceleration and bending injuries of the cervical spine, the visible lesions always arise in the segment that was previously most affected by the degenerative process. Thus, identical traumatic forces can produce widely divergent effects in different individuals, depending on their age and on the state of their intervertebral disks. The varying extent of disk degeneration in different individuals, and the varying magnitude of the causative traumatic forces, often create difficulties of interpretation in the medicolegal assessment of disk trauma.

Sprains of the Motion Segment

Etiology and pathogenesis. The mildest type of injury of the motion segment is the sprain, a stretching or distortion of the intervertebral ligamentous connections and joint capsules without any loss of their continuity. Just as in sprains of the limb joints, any violent bending or twisting of the spine beyond its physiological range of motion can overstretch the ligaments and joint capsules of its motion segments, resulting in injury. Such sprains occur most commonly in the cervical region, and “whiplash” (acceleration–deceleration sprain of the cervical spine) is the best-known example. Motion segment sprain due to violent bending and twisting of the spine is less common in other regions because the external stabilization provided by the rib cage and the paravertebral muscles limits extreme excursions of the joints. The frequent diagnosis of “back sprain” is usually incorrectly attached to cases of lumbago that are actually due to intradiscal tissue displacements of degenerative origin.

Clinical features and treatment. When the inter-and paravertebral ligamentous connections and intervertebral joint capsules are briefly overstretched in a spraining injury, small blood vessels are ruptured, resulting in the formation of post-traumatic hematoma and edema, just as in a sprain of a limb joint. The main clinical finding is painful limitation of movement of the affected region of the spine with reflexive spasm of the musculature. There may also be circumscribed tenderness of the spinous processes of the affected motion segment(s) to percussion and shaking. Plain radiographs show no abnormality except for a possibly abnormal posture (loss of lordosis due to spasm).

The pain and restriction of movement that result from a simple sprain resolve within a few days or weeks as the post-traumatic hematoma and edema are resorbed.