The "age of the disc" was heralded by Mixter and Barr in 1921 when, during surgery, they discovered what they initially thought to be a tumor and was found to be a herniated disc. Since that time the disc has taken a central role in spinal pathphysiology and symptomatology. The advent of CT and MRI, however, has clearly shown that quite frequently, even in the presence of a frank disc herniation, patients remain asymptomatic.
Currently most authors believe that annular tears, leading to disc herniation, occur secondary to repetitive stress, especially torsional stress, in a disc that has already undergone degenerative changes.
Annular tears initially appear in the outer layers of the annu-lus pulposus. Because these layers are innervated, it is reasonable to assume that these tears may elicit axial pain. The tears may progress to involve the whole annular width and subsequently may result in disc herniation. Nucleus pulposus herniation provokes a local inflammatory response, and when it is close to a nerve root, may involve and compress it and bring about radicular pain. Occasionally the herniated disc material loses its connection with the "mother" disc, resulting in a sequestrated disc. The separated piece may migrate in the canal crani-ally or caudally and at times may settle in the lateral recess or within the intervertebral foramen or, rarely, penetrate through the dura. There is ample documentation that extruded discs, even large ones, shrink in size over time and may, over two to three years, disappear altogether.
The direction of herniation, size of the herniated disc, and proximity to the neural elements will, to a large extent, determine the presence or absence of symptoms.
Posterolateral disc herniation will bring about radicular pain. The patient will complain of pain in the upper or lower extremity with or without axial (spine) pain.
Posteriorly directed herniations in the cervical or thoracic region may compromise the spinal cord and bring about progressive neurological deficits with bilateral long-tract signs. In the lower lumbar region posterior herniation of the same size may cause axial pain without any radicular symptoms. Large fragments, however, may compress the whole cauda equina and result in severe neurological compromise. "Pure" lateral herniations that end up in the intervertebral foramen frequently result in unremitting pain due to compression of the dorsal root ganglion (Figures 3-6A, 3-6B, and 3-6C).
Anteriorly directed herniations, however, are frequently seen on imaging studies without any clinical problems.
In the cervical spine the C5-C6 disc is affected most often, followed closely by the C6-C7 disc. Patients affected at these levels frequently complain of numbness and pain in the lateral aspect of the forearm and hand. Herniated discs that compromise the C8 or T1 roots will lead to symptoms over the medial aspect of the arm, forearm, and hand. The pain may increase whenever the patient assumes the upright position or with head movements. Quite often, patients
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