Lumbar degenerative disc disease

Degenerative disc disease of the lumbar spine is caused by age-related wear and tear of the disc, the symptoms of which cause lower back pain that often radiates into the legs.

Synonyms: Herniated or bulging disc, prolapsed disc, herniated nucleus pulposus (HNP).

Between each vertebra is a cushion of fibrocartilage-based structures that provide support and flexibility called the intervertebral disc. This structure is made up of three distinct components: the annulus of fibrous cartilage, the nucleus pulposus and the cartilaginous vertebral plateau.

One of the first articles in the scientific literature to identify the intervertebral disc as a cause of back pain was the article published by Mixter and Barr in 1934 (1)

Mixter and Barr presented a correlation between disc prolapse and the clinical syndromes associated with the resulting nerve and spinal cord compression. They advocated a surgical approach. After their publication of 19 cases, the diagnosis of a “ruptured” disc gained ground in the medical community

Stage of deterioration

Disc deterioration is a normal process

As a person ages, the spinal discs undergo slow wear and tear. This typically involves fibrous changes in the nucleus and organization of the annulus fibrosus rings, and the disappearance of the cartilage endplates. The discs of the lumbar and cervical spine are the most affected. From the age of 20, changes in the lumbar discs can be noticed when the vascular supply to the disc becomes occluded, affecting its nutrition. The posterior portions of the annulus become compressed and bulge under the effect of lumbar lordosis. These posterior annular fibers appear thinner and shorter than the anterior ones. The discs become somewhat wedge-shaped, narrower posteriorly than anteriorly. The nucleus gradually changes from a gel to a fibrous structure; its water-holding capacity decreases while its collagen content increases. The total height of the disc decreases and the disc space narrows.

The posterolateral part of the disc fibers weakens first.

A contributing factor is the functional movements of the spine. These are ten diagonal combinations of flexion and rotation, placing more stress on the posterolateral portion of the annular fibers through the core. Another factor that leads to weakness is that the posterior longitudinal ligament is thicker and stronger than the thinner, more lateral parts of the annulus. Over time, as the posterolateral annular fibers become compressed and swollen, cracks appear between the layers of the annulus. Individual layers of the annulus may separate, allowing nuclear material to seep between them. The cracks may meet and form gaps.

Eventually, these splits and gaps become radial and horizontal tears; the core is allowed to protrude into the annular space. The annular fibers, over time, become weaker and less elastic, creating tension on the outer fibers. This, combined with altered disc mechanics and weight bearing in the spine, promotes bony reinforcement on the outer edges of the vertebrae. Osteophytes form anteriorly and posteriorly. While the discs of the lumbar spine are still able to imbibe water between the ages of 40 and 50, it is during this decade that the nucleus gradually transforms into a fibrous material that is almost indistinguishable from the annular fibers. Then the disc space narrows considerably and the range of motion is reduced. This narrowing occurs in 70% of men and 55% of women between the ages of 55 and 64 (Hertling, Kessler, 1996).

1. A disruption of the normal architecture of the disc (drying out) will eventually cause a fissure.
2. This fissure weakens the annulus fibrosus (which has the role of retaining the nucleus)
3. A severe fissure will result in a migration of the nucleus or a protrusion of the nucleus pulposus, eventually applying pressure on the spinal cord or nerve root and causing radiating pain and specific locations of weakness.

Slightly more than 90% of disc herniations occur at the L4-L5 or L5-S1 disc space, which will impinge on the L4, L5 or S1 nerve root. This compression will produce a radiculopathy (radiation) in the hind leg and dorsal foot.

Drying of the disc with age

When we are born, the disc contains about 80% water. As we age, the disc dries out. This reduces the ability of the discs to act as shock absorbers and makes them less flexible. The loss of fluid also makes the disc thinner and reduces the distance between the vertebrae. As the disc dries, tiny tears or cracks appear in the outer layer (annulus or capsule) of the disc. The gelatinous material inside the disc (nucleus) can be expelled through the tears or cracks in the capsule, causing the disc to bulge, open (rupture) or break into fragments.

Do you know the relative load on your spine, measured at L3-4?

• Lying on your sides (25%)
• Standing at 100
• Sitting at 145
• Standing in flexion – 150
• Sitting in forward
• flexion – 180

• The load is better in a supported sitting position than without support session
• Lumbar support decreases the load.

Unlike other tissues in the body, there is very little blood to the disc, so once a disc is injured, it cannot repair itself and the disc will begin to deteriorate.

Long-Term Outcomes of Degenerative Disc Disease

Disc disease is not the only sign of wear and tear on the spine. The following conditions often run parallel:

• Vertebral osteoarthritis. When the disc loses its structure, the intervertebral space decreases. This causes greater pressure on the facet joints and will eventually wear out prematurely.
• Osteoporosis. Degeneration of the bone structure can increase the risk of vertebral bone fractures, contributing to the overall instability and aging of the spine.
• Spinal Stenosis. A narrowed spinal canal can occur when the discs flatten, stiffen, bulge into the canal or strain the facet joints.
• Degenerative spondylolisthesis. Facet degeneration can cause spondylolisthesis.

differential diagnoses

• Cauda Equina syndrome- medical emergency
  • Urinary retention or incontinence, decreased sexual function
• Lumbar sprain or strain, SI syndrome
• Spondylolisthesis or instability
• Spinal canal stenosis
• Piriformis syndrome
• Tumor (multiple myeloma or metastases)
• Infection (meningitis)
• Osteoarthritis (rheumatoid or ankylosing spondylitis)

Degenerative cascade

Kirkaldy-Willis describes the degenerative cascade as the necessary reaction of the vertebral body to a degenerated disc.

Faced with a torsional injury to the disc. Its environment responds in 3 stages.

1. Dysfonction

Small circumferential tears in the outer layer of the disc develop inward. After an injury, mobility may be limited.

2. Relative instability

The inner disc material begins to protrude outward through the tears, causing the disc height to decrease.

3. Recovery

Osteophytes form on the edges of the disc and the disc changes become fixed. The spinal segment stabilizes and the dysfunction subsides.

Symptoms

Low back pain 

Lombalgie : Les douleurs dorsales sont fréquentes dans la deuxième décennie, la discopathie et la hernie discale dans la troisième ou quatrième décennie. L’histoire habituelle de la hernie discale lombaire est une douleur lombaire répétitive, irradiant vers les fesses et soulagée par le repos. La douleur est augmentée par des épisodes de flexion, de position assise, d’effort, d’éternuement, de toux, etc. La douleur est diminuée par le repos et la position fœtale.

Radiculopathy

This refers to pain in the distribution of the sciatic nerve and is invariably caused by a herniated disc. This is called sciatica. Pain in the legs equal to or greater than pain in the back highlights root pain due to nerve root compression from a herniated disc. The pain usually begins in the lower back and radiates to the sacroiliac, buttock and thigh areas. Root pain usually extends below the knee.

Nerve root compression 

Approximately 95% of disc prolapse occurs in the L4-5 region, compressing the L5 nerve root. Other commonly involved nerve roots are L4 and S1 due to disc prolapse between L3-4 and L5-S1 showing respectively the different clinical manifestations following nerve root compression.

• Osteoarthritis refers to degenerative changes in the synovial joints.
• Disc disease refers to degenerative changes in the intervertebral disc.
• Spondylosis is a degenerative process of the green spine

References

1. Mixter WJ, Barr JS. Rupture of the intervertebral disc with involvement of the spinal canal. N Engl J Med. 1934;211:210–215