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Spine problems, running the gamut of low back or neck pain to major serious degenerative or traumatic conditions requiring surgery, are one of the medical conditions afflicting western society today and one of the most common problems seen by neurosurgeons. Problems involving the low back and neck range from simple sprain and muscle spasm conditions associated with over exertion or poor physical conditioning that are treated conservatively to severe degenerative conditions requiring major surgical procedures. (For more information about conservative treatments see the Pain Institute)
Though lumbar disc herniation and spinal stenosis are specific conditions within the overall category of spine problems, it is best viewed within the overall context of degenerative spine conditions. The reasons for the ubiquitous presence of spine problems in modern life are not entirely known but are thought to be due to a confluence of evolutionary, anatomic and social factors. The assumption of the upright posture for walking is a relatively recent development in evolutionary terms, and as such the lumbar spine may not be fully adapted to the major forces placed on it during a lifetime of normal human activities. The modern sedentary lifestyle leads to poor conditioning of the supportive cervical, abdominal and lumbar muscles respectively surrounding the spine and transmits forces to the bony and ligamentous structures which leads to deterioration. Although this can occur at all spinal levels, the lower aspect of the lumbar spine is particularly prone to deterioration because it bears the full weight of the upper body and is subjected to significant axial forces during various types of activities. In addition, the lower lumbar region adjoins the rigidly fixed sacrum and hip structures through which applied loading forces cannot be dissipated as they can at upper spinal levels. Similarly in the cervical spine the disease is most often centered at C5/C6 or C6/C7 where most of the normal motion occurs.
The vertebral body portion of each specific vertebrae is joined to the one above and below by the cartilaginous pad known as the disc. This consists of a dense layer of cartilage which is firmly attached to each adjacent vertebral body with a circumferential rim known as the annulus fibrosus. The central aspect of the disc contains a substance known as nucleus pulposus, a spongy gelatinous material composed mostly of water. Posterior elements of each vertebral body, consisting of the pedicle, pars interarticularis, laminae and facet complexes are also very important to the overall support of the spinal column and as can be seen, dense ligaments attach the adjacent vertebral bodies at these points also.
From a functional standpoint, when considering normal and abnormal motion in the spine, a functional spinal unit consists of the lower and upper halves of two adjacent vertebral bodies with the intervening disc and complex of posterior elements associated with these two vertebrae. Interestingly, on cadaver studies of young, healthy individuals the disc structures are so strong that a major distractive force placed on a lumbar functional spinal unit, the vertebrae itself will break prior to loss of disc integrity. It is only after deterioration occurs in the disc, with weakening of the outer annular fibers and desiccation of the nucleus pulposus that continued stress or trauma upon the lumbar spine can lead to disc herniation. Disc herniation itself can occur in conjunction with other processes which occur during spinal degeneration such as spondylosis with osteophyte formation. (See Lumbar Spinal Stenosis).
Although many other medical, psychological and social factors can influence the presentation and natural history of spinal disc disease, a classic presentation can be summarized as follows: a generally healthy middle aged person is evaluated for neurosurgical referral after a brief history of severe lancinating pain radiating across the back or neck, down the arm or in the distribution of the sciatic nerve extending from the lumbar spine posteriorly through the buttocks and thigh often with radiation into the anterior (frontal) aspect of the calf with paresthesia (tingling) or numbness into the foot or hand. Quite often these patients describe a history of intermittent low back or neck pain in the past without leg or arm pain that is usually resolved with conservative treatments such as rest or anti-inflammatory medication. They often state that their back pain recurred after a recent episode of strain while lifting a heavy object or engaging in sports, etc. although often there is no specific antecedent event. Back or neck pain was present for a few days and then subsided. Leg or arm pain then became predominant and quite severe often necessitating bed rest and marked limitation of activity. The pain is lancinating in quality and is often made worse by standing, lateral bending or valsalva maneuvers ("holding breath") such as straining at stool or bending.
The majority of cervical herniations occur at C5/C6 and C6/C7 while the lumbar disc herniations occur usually at the L4/L5 level with another significant occurrence being at L5/S1. Upper lumbar or cervical levels are much less common. Herniations in the thoracic spine are quite rare and often present as painless difficulty walking. Radiculopathy refers to a dysfunction of a nerve root usually due to mechanical compression. In this context it is usually due to a herniated disc or bone spur. Myelopathy refers to compression of the spinal cord. Deteriorated nucleus pulposus will leave its normal contained area within the disc and express itself through a weakness or tear in the posterior longitudinal ligament.
Degrees of lumbar disc herniation can be graded along the continuum as follows:
- a "bulge" where disc material has pushed through deteriorated annular fibers but is still contained by an outer rim of intact annulus
- protrusion where disc material has extruded through a defect in the annular ligament but is still connected to the central nucleus pulposus
- disc herniation where the nucleus broke through the anulus
- an extrusion where a fragment of disc material has completely left the disc compartment
- sequestration refers to a fragment of disc material traveling in the epidural space away from the disc space from which it originated.
Defects in the annulus, allowing disc herniations, normally occur on the lateral aspect of the spinal canal astride the posterior longitudinal ligament. Central herniations are rare but if large enough could have catastrophic results by compressing the spinal cord or cauda equina and causing paralysis in all four extremities or loss of bowel/bladder function respectively.
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