Degenerative Spinal Disorders
Trauma or cumulative wear and tear from age can result in disc herniations, a condition in which the annulus ruptures, allowing disc material to escape, most often posteriorly or posterolaterally. This disc material can occupy space in the canal or neural foramen, potentially compromising the cord or nerve root at that level (Figure 5). If the nerve root is compressed or irritated by the disc material, radiculopathy may result. Radiculopathy characteristically causes pain along the nerve root distribution, sensory disturbance, and/or weakness in a myotomal distribution. See Figure 6 (below) for a patient pain diagram typical for radicular-type pain.
Figure 5.
Axial MRI of a patient with right-sided disc herniation at L4-L5.
Figure 6.
S1 radicular-type pain illustrated on a patient pain diagram.
Legend: Ache ^ ^ ^ ^, Numbness o o o o, Pins & Needles = = =
=, Burning X X X X, Stabbing / / / /
If stenosis in the cervical or thoracic regions becomes severe, or a large disc herniation is present, myelopathy may result; a condition in which the cord is significantly compressed. Motor and sensory function can be compromised as well as bowel and bladder function. Patients with myelopathy will often have difficulty with balance and gait. Permanent changes in the spinal cord can develop. Clinical findings include muscle atrophy in the hands, long tract signs, (hyperreflexia, clonus, positive Babinski and Hoffman's tests), sensory changes and motor weakness. (29)
In large lumbar disc herniations, enough pressure can be exerted on the nerve roots within the canal below the level of the conus medullaris to cause cauda equina syndrome. Cauda equine syndrome is a global dysfunction of multiple nerve roots, often causing a mixed picture of motor, sensory, bowel and bladder dysfunction. (32) This is a surgical emergency.
The ability of the spinal canal to tolerate narrowing from a disc herniation before neurologic symptoms occur differs, because the canal size is relatively wider in relation to cord size in the lumbar and cervical regions than in the thoracic region. (26) Moreover, as degenerative changes progress and begin to diminish the canal size, relatively small disc herniations can cause symptoms because of the resulting relative canal stenosis. (28)
Many pain generators exist in and around the spine. The outer one third of the annulus contains pain nerve fibers, as does the posterior longitudinal ligament and the capsule of the facet joint. (28,33) Muscles can be a source of pain. Degenerative changes within the disc and facet joints can cause pain. (33) Irritation of nerve roots by disc herniations and spinal canal stenosis with pressure on the spinal cord can cause pain. (27,30) Diagnosing the pain generator in order to make an appropriate treatment plan can be a daunting task, difficult at times for even the most experienced spine specialist. Thus, an accurate and thorough work up is imperative to reduce misdiagnoses and/or unnecessary surgical interventions.