ORIENTATION OF THE T-LUMBAR FACET JOINTS - ASSOCIATION WITH DEGENERATIVE DISC DISEASE

The orientation of the lumbar facet joints was studied with magnetic r esonance imaging in 140 subjects to determine if there is an associati on between facet tropism and intervertebral disc disease or between th e orientation of the facet joints and degenerative spondylolisthesis. The 140 subjects were divided into four groups: sixty-seven asymptomat ic volunteers, forty-six of whom did not have a herniated disc on magn etic resonance scans (Group I) and twenty-one who did (Group II); fort y-sis symptomatic patients who had a herniated disc confirmed operativ ely (Group III); and twenty-seven patients who had degenerative spondy lolisthesis at the interspace between the fourth and fifth lumbar vert ebrae (Group IV), Axial scans were made at each lumbar level and digit ized, and the facet joint angle was measured by two independent observ ers with use of image analysis software in a personal computer. The te chnique of measurement of the facet angles on magnetic resonance scans was validated with a subset of subjects who also had computed tomogra phy scans made. Similar values were obtained,vith the two methods (r = 0.92; p = 0.00001), For the forty-six asymptomatic volunteers who did not have a herniated disc on the magnetic resonance scans (Group I), the median facet tropism was 5 to 6 degrees and was more than 10 degre es in 24 per cent (eleven) of the subjects, There was no association b etween increased facet tropism and disc degeneration. At the level of the fourth and fifth lumbar vertebrae, the median facet tropism was 10 .3 degrees in the symptomatic patients who had a herniated disc at the same level and 5.4 degrees in the asymptomatic volunteers (Group I) ( p = 0.05), The mean orientation of the lumbar facet angles relative to the coronal plane was more sagittal at all levels in the patients who had degenerative spondylolisthesis, The greatest difference was at th e level of the fourth and fifth lumbar vertebrae (p = 0.000001). The m ean facet angle was 41 degrees (95 per cent confidence interval, 37.6 to 44.6 degrees) in the asymptomatic volunteers and 60 degrees (95 per cent confidence interval, 52.7 to 67.1 degrees) in the patients who h ad degenerative spondylolisthesis. Furthermore, both the left and the right facet joints were more sagittally oriented in the patients who h ad degenerative spondylolisthesis. An individual in whom both facet-jo int angles at the level of the fourth and fifth lumbar vertebrae were more than 45 degrees relative to the coronal plane was twenty-five tim es more likely to have degenerative spondylolisthesis (95 per cent con fidence interval, seven to ninety-eight times), The increase in facet angles at levels other than that of the spondylolisthesis suggests tha t increased facet angles represent variations in anatomy rather than a secondary result of spondylolisthesis.