Osteochondrosis of the spine: neurological complications

Beginning with Hildebrandt (1933), who proposed the designation of an "osteochondrosis of the intervertebral disc" to define a vast degenerative process that affects not only the cartilage but also the subchondral part of adjacent vertebrae, this term has become widespread in the work of morphologists, radiologists and clinicians.

The term "osteochondrosis of the spine" (OP) refers to a primarily developing degenerative process in intervertebral discs, which in turn leads to a secondary development of reactive and compensatory changes in the osteochondrosis apparatus of the spine.

Intervertebral discs that make up about 1/4 the length of the entire spine, play a large role in the biomechanics of the spine: they serve as ligaments and peculiar joints, and they are buffers that soften the tremors that fall on the spine. A certain importance is attached to the pulpous core, which has a high degree of hydrophilicity, the water content of which reaches 83%. The unusual hydrophilicity of the core greatly exceeds the hydrophilicity of other tissues of the human body.

In the process of degeneration, the discs lose moisture, the core dries up and disintegrates into separate fragments, the fibrous ring loses its elasticity, softens, thins, and the disk shows cracks, tears and cracks that dot the disc in various directions. Initially, cracks are formed only in the inner layers of the ring and the kernel sequestration, penetrating into the crack, stretch and protrude the outer layers of the ring. When the cracks propagate through all the layers of the ring, either the individual sequesters of the nucleus, or all of it, fall through this defect into the lumen of the spinal canal. In these cases, the integrity of the posterior longitudinal ligament can be impaired.

Due to the defectiveness of the pulp nucleus, it now involves not only tangential, but also vertical loads. All this, firstly, causes prolapse of the fibrous ring beyond the disk, and secondly, contributes to its instability. In addition, due to the loss of elastic properties, the fibrous ring can not retain the pulpous nucleus or its fragments, which creates conditions for hernia formation.

At a certain stage of development of degenerative changes, the disc may bulge without breaking the fibrous ring, which is termed the protrusion of the disc. The bulging area of the disc is vascularized, fibrous tissue grows in it, and in the later stages, calcification is observed. In cases where there is a breakthrough of the fibrous ring with its exit beyond the part or the entire pulpous nucleus, which is more often observed in young people after acute trauma, they are already judging about "prolapse or disc herniation".

Depending on the direction of prolapses or hernia, the following types are distinguished:

• the anterior and lateral, proceeding mostly asymptomatic;
• posterior and posterolateral, penetrating the vertebral canal and intervertebral foramen and often causing compression of the spinal cord and its roots;
• central prolapse (Schmorl's hernia), in which the tissue of the disc penetrates through the degenerate altered part of the hyaline plate into the spongy mass of the vertebral body, forming in it grooves of various shapes and sizes; they are an x-ray finding, without manifesting themselves clinically.

When the disc degenerates with the approach of the vertebral bodies, the facets of intervertebral joints and vertebral bodies are displaced, and the mechanism of their movements changes. Degeneration of discs is accompanied by secondary changes in the bodies of the vertebrae, which consist of two concurrent processes:

• degenerative-dystrophic changes in the subchondar bone, which occur only after the disintegration and disappearance of the hyaline plates of the disc;
• reactive neoplasm of bone tissue in vertebral bodies, expressed in sclerosis of subchondral bone tissue with the formation of marginal bone growths - osteophytes. These arthritic sprains of the bone are designated by the term "spondylosis".

Developing at the same deforming arthrosis in the form of growth of articular surfaces of the spine in the places of greatest load is designated by the term "spondylarthrosis or osteoarthrosis". Osteophytes located in the lumen of the spinal canal, as well as protrusions and prolapses of hernias, can cause symptoms of compression of the spinal cord and its roots.

As a result, the disorganization of the biomechanics of the vertebral bodies adjacent to the affected vertebral motor segment (PDS) increases, and the spine-ability of the spine loses its consistency and rhythm. The amazed PDS itself acquires an unphysiological, often fixed, installation, most often kyphotic. This entails hyperlordosity and hypermobility of the superior PDS, which in the beginning act as compensatory, but in the future can contribute to the identification and strengthening of the dystrophic process with the consequent spread of it to an increasing number of PDS.

Instability in PDS is one of the most frequent pathomorphological substrates of neurological syndromes. Most often, instability is revealed at the level of segments C ₄ _ ₅ and L ₄ _ ₅.

Segmental instability arises as one of the earliest manifestations of the dystrophic process in any of the constituent elements of the PDS leading to a disturbance of its harmonious function, and is manifested by excessive mobility between the elements of the PDS. As a result, an excessive degree of flexion and extension in the PDS, as well as slipping anterior or posterior.

In the pathogenesis of the development of instability, the main significance is the dystrophy of the fibrous ring, which loses its elasticity and the proper fixation capacity. Slipping of the overlying body of the vertebra against the underlying causes the rupture of the fibrous ring, the loss of the turgor by the pulpous nucleus, and the involvement of the posterior parts of the PDS, in particular the intervertebral joints, into the dystrophic process, which is accompanied in the expressed cases of instability by the development of extensor subluxation in them. To subluxation, in addition, the constitutional weakness of the ligamentous apparatus predisposes.

In connection with excess mobility in the PDS, a number of consecutive structural, biomechanical and reflex changes develop:

• the skewed anterolateral angle of the body of the underlying vertebral body is formed;
• a "traction spur" is formed;
• the formation of neoarthrosis in the area of contact of the articular process and the arch.

In connection with the compensatory reflex tension of segmental muscles at a certain stage, segmentation may occur in one or another posture (kifosis, hyperlordosation). These changes are due to both pathogenetic and sanogenetic mechanisms. The predominance of the latter can lead to fibrotization of the disc and the elimination of, thus, instability. Fixation of the PDS is also promoted by the development of intervertebral spondylarthrosis. However, with unstable instability, both reflex and reflex-compression, compression-reflex and rarely compression syndromes can develop.

It depends on the following situations and the relationship between the tissues of the PDS and the neurovascular formations with instability:

• excess mobility in the segment determines the irritation of the receptors in both the fibrous ring and in the disc-related sections of the anterior and posterior longitudinal ligaments; and in capsules of intervertebral joints;
• the development of subluxation of Kovac at the cervical level causes traumatization of the vertebral artery with its vegetative plexus. The latter is possible with excessive movements in the PDS, certain motor loads and the absence of subluxation in the joint;
• a pronounced subluxation in the intervertebral joint can be accompanied by a shift of the apex of the articular process toward the intervertebral foramen and become the cause of its narrowing, which under certain conditions may lead to compression of the root and radicular artery;
• significant slippage in the back with combination with some additional factors (congenital canal narrowness, compensatory development of posterior marginal bone growth) can lead to narrowing of the spinal canal and serve as a condition for the development of compression or vascular spinal syndrome.

Pathological effects (irritative or compression) are possible not only as a result of direct contact between altered bone-cartilaginous structures of the PDS and vascular-neural structures, but also because of the diminution of the spaces in which these formations are located. In particular, we are talking about intervertebral openings and the vertebral canal.

Narrowing of the intervertebral foramen can be caused by the following changes in the tissues of the PDS:

• decrease in the height of the interbody spacing due to disk dystrophy (correspondingly, the vertical size of the orifice decreases);
• marginal bony expansions of the deforming type in the region of intervertebral joints (narrowing mainly the horizontal size of the hole);
• unco-vertebral growths, marginal bony growths of the bodies and disc herniations on the lumbar and thoracic levels;
• dystrophically altered yellow ligament.

Narrowing of the spinal canal in connection with dystrophic changes may be due to:

• posterior hernias of the disc;
• posterior marginal bony expansions of vertebral bodies;
• hypertrophied yellow ligament;
• the slipped body of the vertebra with pronounced instability;
• cicatricial-adhesive changes in the epidural cellulose and the membranes of the spinal cord.

Narrowing of the spinal canal is accompanied by predominantly compression or compression-reflex effects.

Sanogenetic mechanisms are directed, naturally, to the elimination of narrowing and are associated with the possibility of correcting hernial protrusions, improving circulation in the spinal canal, resorption of dystrophically altered tissues.

Disorders of biomechanical relationships in the kinematic chain of the spine in combination with other pathogenetic mechanisms contribute to the development of the myodiscoscope process in the muscles of the PDS, spine and extremities. At the same time, complex synergistic reciprocal and other reflex processes develop with violation of the stonokinetics of the spine. First of all, its configuration changes in connection with changes in the tone of the spine muscles, seeking to compensate for the failure of the function of the PDS, - lordosis is smoothed or kyphotic system is developing in the department, and in some cases, a scoliotic setting occurs in connection with the transfer of support to the foot of the unaffected side. In the formation of these changes, the multiarticular muscles of the back, and small intersegmental muscles also participate. At a certain stage, these compensatory mechanisms are sufficient. However, with the duration of the tonic tension of the muscles, they develop dystrophic changes. In addition, in connection with the formation of a pathological reflex ring, the muscle tension from the sanogenetic mechanism turns into its opposite, a pathological contracture. As a result, the load changes not only in the muscles of the spine, but also in the muscles of the limbs that function in the new conditions, which leads to myoadaptive postural and vascular myodystonic and miodystrophic changes in them.

In connection with dystonic and dystrophic changes, the muscles become a source of pathological afferentation addressed to the same segments of the spinal cord that innervate the affected PDS, as well as to the polysegmentary inter-neural apparatus with the involvement of the entire spine and limbs in the process of muscles.

Thus, a pathogenetic ring is created, supporting, aggravating and developing the pathological process in osteochondrosis of the spine. The emergence of new biomechanical conditions and the pathological condition of such an important motor organ as the spine leads to a restriction of mobility not only of its individual parts but also of general motor activity, which contributes to the disruption of the adequate activity of motor visceral reflexes that are of great importance for the optimal metabolic-trophic providing motor activity.

The most common neurologic complications of the osteochondrosis of the spine are found in the cervical and lower lumbar regions.

The main factors in the development of neurological complications in cervical osteochondrosis of the spine are the following.

1. Relatively constant compression of the spinal cord, its roots with their vegetative fibers, the vertebral artery with its sympathetic plexus and the ligamentous apparatus of the spine with its innervation apparatus.

• In the cervical region, a disc herniation is relatively rare; most often only protrusion of the disk is formed here.
• Compression syndromes are a consequence of posterior bone osteophytes. Un-co-vertebral joints are not true, they are prone to deforming arthrosis; while osteophytes are sent either backward, into the intervertebral foramen, acting on the nerve roots, or outward, causing compression of the vertebral artery or its sympathetic plexus.
• The narrowing of the intervertebral foramen in the anterior part usually occurs due to unkovertebral bone growths, in its posterior part due to spondyloarthrosis due to intervertebral joints, Kovacs subluxation and thickening of the yellow ligament, and a decrease in the vertical size of the disc leads to a decrease in this size of the intervertebral foramen due to the convergence of the bodies adjacent vertebrae.
• Unfavorable circumstances are the departure of the roots of the spinal cord in this section at a right angle to it (and not vertically, as at other levels), a small length of the radicular nerve (no more than 4 mm), lack of elasticity and sufficient mobility of the radicular cuffs.
• Naturally, in pathological conditions there is a violation of blood and lymph circulation within the narrowed intervertebral foramen with the development of venous stasis, edema with cicatrization, a clinical manifestation of irritative and degenerative radicular symptoms.
• The possibility of compression effects on the spinal cord from the side of the yellow ligament. With increased loads, the thickening of the yellow ligament with fibrosis gradually develops, and when the cervical region is sharply rebound (especially sudden) conditions are created for infringing the ligament between the vertebra arches and for pressure on the posterior parts of the spinal cord.

2. Microtravmatization of the spinal cord, its membranes, rootlets, vascular system and ligamentous apparatus of the spine that periodically arises during a long time during the movements of the spine.

• Studies Reid (1960), concerning the dynamic relationship between the spinal cord and spine in normal, revealed significant mobility of the spinal cord and dura in the oral and caudal directions with flexion and extensional movements of the head and spine. With inflexion, the length of the spinal canal (mainly in the C2-Th1 region) can increase to 17.6%, and accordingly, the spinal cord stretches and slides up along the front surface of the canal. Naturally, in conditions of instability of the cervical vertebrae (discs), the tension of the spinal cord and roots may increase and traumatization of the neural formations is especially evident in the unevenness of the anterolateral sections of the spinal canal in connection with the presence of osteophytes and subluxation. When forced neck flexion in the case of a posterior osteophyte, the brain tends to stretch above it, increasing compression and traumatizing brain tissue. Osteophytes can exert periodic effects (as a consequence of microtraumas with changes in the position of the vertebrae) on nerve formations embedded within the posterior longitudinal ligament and dura mater, which is manifested by painful and, probably, reflex phenomena. In this sense, the development of the subluxation of the vertebra is also important. Traumatization of the spinal cord increases if there is an imbalance of the discs, and for flexion and extensional movements one vertebra slides and shifts along the surface of the other.
• Osteophytes formed in the area of the unco-vertebral articulation, heading into the intervertebral foramen and towards the vertebral canal, can cause the syndrome of the vertebral artery and its sympathetic plexus.

The compression of the vertebral artery with its sympathetic plexus can be relatively constant, and it can also occur periodically at times of change in the position of the head and neck. Irrigation of sympathetic fibers or impaired blood circulation in the vertebral artery system of a mechanical or reflex character often occurs when the position of the head and neck changes.

For the development of the vertebral artery syndrome, the subluxation of Kovacs has a certain significance. In such patients, the forward deflection of this artery is observed predominantly in the position of extension of the neck.

3. Vascular ischemia and its significance in the clinical syndrome of brain compression in cervical spondylosis.

The compression of the anterior spinal artery system can be a consequence of the direct action of the posterior osteophyte or disc hernia, as well as the compressive effect of these formations at the time of the change in the position of the neck.

4. Involvement in the pathological process of the peripheral and central parts of the autonomic nervous system.

The reflex effects of pathological impulses originating from the spinal cord, its roots with their vegetative fibers, the vertebral nerve, which is the branch of the stellate node, and the ligamentous elements of the spine with its innervation apparatus, are manifested by a variety of sympathy and neurodynamic disorders.

In the initial stage of the disease, posterior osteophytes or a bulging disc often cause only compression and stretching of the anterior and posterior longitudinal ligaments; while the remaining ligamentous apparatus of the spine may be involved in the pathological process. The ligamentous apparatus of the spine, primarily the anterior and posterior longitudinal ligaments, as well as the dura mater are innervated mainly by sympathetic sensitive branches of the sinuvertebral nerve (recurrent meningeal nerve) consisting of a meningeal branch extending from the posterior root and twigs from the connecting branch of the border sympathetic post.

Nerve endings are revealed both in the posterior (due to the sinuvertebral nerve) and in the anterior longitudinal ligaments, and there is reason to believe that the irritation of these ligaments is manifested by pains in the back of the neck with irradiation into the suboccipital, interscapular area and both forearms.

Thus, the degenerated cervical disc can be viewed, on the one hand, as a source of pain manifestations, and on the other hand, pathological impulses that, when switched through the CNS, cause reflex disorders in the neck, shoulder girdle and hand.

[1], [2], [3], [4], [5], [6], [7], [8], [9]