A MR Study of the Influence of Lumbar Facet Geometry in Intervertebral Disc Degeneration

The purpose of this study was to evaluate the relationship of facet geometry (facet angle and tropism) to the water content of the lumbar intervertebral disc. Magnetic resonance (MR) imaging of 51 subjects, 22 women and 29 men, less than 50 years of age, were analyzed. Axial MR images were used to measure the facet angles and then determine facet tropism. For each intervertebral disc, water content was calculated by obtaining a T2 relaxation time from pulse sequence parameters with TR/TE of 2,000/30;100. There are three trends noted in the lower lumbar spine: 1) Decreased water content is found in the intervertebrl disc (IVD) of the lower lumbar spine. 2) Facet angles increase in the lower lumbar spine. 3) Tropism is found more frequently in the lower lumbar spine. A significant reduction of intradiscal water content was noted in the presence of disc degeneration (p＜0.0001) or in the group with facet angles greater than 30º (p=0.015). There was a mild correlation of intradiscal water content to the magnitude of facet angles (r=0.3 1, p＜0.00 1) for the entire group, but not at each level, L1-2 to L5-S1 (p＞0.05). Subjects with tropism also had no significant relation to the amount of water content at each level (p＞0.05). It was concluded that the risk of disc degeneration is increased whenthe facet angle is more than 30º , and a degenerating disc occurs with a decreasing of the water content.