Chapter 13. Degenerative spine disorders

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13.1. Etiology, pathogenesis, classification

Degenerative spine disorders occur in the vast majority (98−99%) of adult people of developed countries. The spine is a complex movable supporting structure. The main load in it falls on the intervertebral discs, consisting of an elastic cushioning nucleus pulposus and a fibrous ring surrounding the nucleus. The disc is connected to the upper and lower vertebrae through cartilaginous hyaline plates. With age, the water content in the discs and their elasticity decrease significantly. The small vessels supplying the disc are obliterated by 20−30 years, and metabolic processes in the disc are carried out by diffusion.

The causes of this pathology have not been definitively clarified. Since degenerative changes of the spine occur more often in residents of developed countries, it is believed that they are based on the peculiarities of nutrition and lifestyle. Thus, among the poorest segments of the population of Southeast Asia, the frequency of pronounced degenerative changes in the spine is only about 30%, while among the affluent residents of the same regions, almost 100% of adults experienced back pain.

Biomechanics of the spine affects the localization and severity of degenerative changes. The normal cervical and lumbar lordoses provide greater pressure on the anterior parts of the disc, and as degenerative changes in the fibrous ring progress, the gelatinous nucleus (also degeneratively altered) begins to shift in the posterior direction. The bulging of the posterior parts of the disc into the spinal canal leads to the displacement of the periosteum and the formation of reactive bone changes in this zone referred to as osteophytes. The X-ray picture of such changes is referred to as spondylosis. If intervertebral joints are involved in the process, spondyloarthrosis is diagnosed.

Thick longitudinal connective tissue ligaments course along the anterior and posterior surfaces of the spine, which make the spine structure even more durable. The posterior longitudinal ligament strengthens the middle sections of the surface of the fibrous ring facing the spinal canal, preventing the displacement of the intervertebral disc in this direction. At the same time, the lateral surfaces of the discs, especially in the lumbar region, where the posterior longitudinal ligament narrows, are less durable. Thus, in most cases, the bulging of the cervical or lumbar intervertebral disc occurs in the posterolateral direction (Fig. 13.1).

Fig. 13.1. The mechanism of formation of a herniated intervertebral disc: 1 — fibrous ring; 2 — gelatinous nucleus; 3 — herniated disc

Different divisions of the spine experience different loads. A particularly significant load falls on the discs of the lumbar and cervical divisions, since these divisions are characterized by the greatest mobility. This is probably due to the fact of the predominance of degenerative disease of the cervical and lumbar spine.

The degenerative process in the intervertebral disc conditionally passes through three stages.

At stage I, there is a decrease in the concentration and a change in the properties of glycosaminoglycans and collagen of the nucleus pulposus, which leads to a decrease in intradiscal pressure and a decrease in the water content in the nucleus; at the same time, a fibrous process develops, as a result, the cushioning properties of the nucleus decrease, and with any significant load, microtraumatization of the fibrous ring occurs with the appearance of cracks in it.
At stage II, fragments (sequesters) of the nucleus pulposus are squeezed into the spinal canal through cracks in the fibrous ring. The thickness of the intervertebral disc decreases (“disc settlement”).
At stage III (final), the disc is completely replaced by coarse-fibrous connective tissue, which is often ossified.

Clinically and radiologically, there are three main forms of degenerative disease of the intervertebral disc.

Disc protrusion. The degeneratively altered disc protrudes into the lumen of the spinal canal, but the integrity of the fibrous ring is not macroscopically impaired, the posterior longitudinal ligament is not damaged (Fig. 13.2). The protrusion of the disc presents with a painful, muscular-tonic syndrome.

Fig. 13.2. Common degenerative disease of the lumbar spine: degeneration, decrease in height and protrusion of intervertebral discs L_III–L_IV, L_IV–L_V, L_V–S_I. Magnetic resonance imaging, T2-weighted image

Disc herniation is more pronounced than protrusion, the spread of the substance of the gelatinous nucleus into the spinal canal with overgrowth or rupture of the fibrous ring and the posterior longitudinal ligament (Fig. 13.3). Clinically, it is manifested by signs of compression of nerve structures at the level of the damage (nerve roots, spinal cord, ponytail).

Fig. 13.3. Herniated intervertebral disc L_V−S_I, degeneration of discs L_II−L_III and L_IV−L_V. Magnetic resonance imaging, T2-weighted image

Sequestered disc herniation. A free fragment of the disc in the spinal canal may be located above or below the corresponding intervertebral disc (Fig. 13.4). The clinical presentation depends on the degree of sequestration compression of nerve structures.