Ab Figure

Flexion and extension lateral plain films of the cervical spine demonstrating instability due to degenerative disc disease. A subluxation is noted at C4-C5 in (A) flexion view (arrow) with full correction on extension (B).

cervical lordosis or, quite commonly, reversal of the cervical lordosis —cervical kyphosis. A congenitally narrow cervical canal is a significant risk factor for the development of myelopathy once degenerative changes occur. The Torg-Pavlov ratio can be obtained by dividing the sagittal diameter of the cervical spinal canal by that of the vertebral body as obtained in lateral spine films. In normal individuals the ratio is one. A ratio of 0.8 or less helps identify patients with a high risk of developing this disease (Figure 4-5). In the lumbar region degenerative scoliosis is quite commonly seen. Oblique films of the cervical spine and lateral films of the lumbar spine frequently show single or multilevel neural foraminal narrowing. A posterior disc height of less than 4 mm or foraminal height of less than 15 mm is an indicator of potential foraminal stenosis.

Spinal MRI is most useful in delineating the location and extent of stenosis. Both modalities will clearly show the severity of the disease and delineate the anterior and posterior structures that are the cause of the stenosis. In the cervical region the canal is frequently encroached upon by posteriorly directed ridges, calcified herniated discs, and hypertrophic and, at times, ossified posterior longitudinal ligament. From the back the canal may be encroached upon by hyper-trophic facets and thickened ligamenta flava (Figures 4-6A and 4-6B). In the lumbar spine hypertrophic facets and thickened ligamenta flava are the most common offending structures. Not infrequently facet cysts play a role in symptom production (Figures 4-7A and 4-7B). The spinal canal may be further compromised by degenerative unstable segments.

In the cervical region, facet hypertrophy in combination with uncovertebral joint hypertrophy compromise the neural foraminae and lead to nerve root dysfunction. MRI of the cervical spine, in sagittal and axial cuts, will provide invaluable information about the spinal cord. Quite frequently an increased cord signal is seen on T2-weighted images of the compressed segments. The increased signal represents

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