The relationship of facet tropism to degenerative disc disease.

The role of facet tropism (asymmetry) in the pathogenesis of degenerative disc disease is unknown, and several conflicting reports have been published. We studied this association using CT/discography performed at 324 lumbar levels (108 patients). The stage of disc degeneration as well as the patient's pain response upon discographic injection were scored using a standardized protocol. The facet angles were measured directly from the axial CT/discographic images and defined, in each case, as the angle formed by the facet orientation with respect to the midsagittal plane. The facet tropism angle was defined as the difference between the left and right facet angles at each disc level. The mean and standard deviation (SD) of the tropism angles were calculated. From this calculation, each pair of facet joints was classified as symmetric (within 1 SD of the mean), moderately asymmetric (between 1 and 2 SD), or severely asymmetric (beyond 2 SD of the mean). There were no differences in degree of disc degeneration or pain response with respect to the facet tropism. The total facet angle was also studied. The total facet angle was greater at the more caudal levels. The total angle size was not associated, however, with disc degeneration or pain provocation. These findings do not support the hypothesis that there is an association between facet tropism and degenerative lumbar disc disease.