Central stenosis in the elderly is the result of a combination of factors. Disc degeneration and collapse of the disc results in a uniform bulging of the posterior annulus, which encroaches the neural canal surface. In some cases symptoms are present only in sagittal extension as a borderline stenosis may appear only in this position . Dynamic assessment techniques are welcome in those cases (Fig. 1). Also as a result of disc collapse a secondary zygapophyseal arthrosis with facet hypertrophy occurs, further diminishing the central canal at the intervertebral level. Degenerated facet joint, when showing medial hypertrophic changes, may also participate in the canal stenosis (Fig. 2).
Due to this disc collapse and decrease in intervertebral height the often thickened ligamentum flavum  may buckle , thus further decreasing canal space at the disc level. Furthermore, fibrotic chondrometaplasic changes and even ossification of the ligamentum flavum may also occur [20, 24, 28, 29]. This reduces the elasticity of the ligamentum, which may then bulge in the canal even if it keeps a normal thickness . Several studies have shown a higher frequency of calcification of ligamentum flavum in stenotic than nonstenotic subjects . The extent of these histological changes appears to be correlated with
age . It must, however, be stressed that in the elderly central and lateral lesions very often both participate in the stenostic pathology (Fig. 3).
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