The Relationship between Facet Joint Morphology and Flexion-extension Movement
Previous studies reported on the relationship between facet tropism and disc degeneration and disc herniation, but results were conflicting. Nineteen fresh cadaveric spines were used. A total of 25 motion segments were studied. The frozen lumbar motion segments were imaged in the direct axial and sagittal projections in a CT scanner. The motion segments were loaded to 5.7 Nm in flexion or extension. After flexion or extension loading, the specimens were frozen. The frozen motion segments were imaged again by CT scan. A total of 6 parameters were digitized and measured directly from the CT images. The facet joints were more sagittally oriented proximally and gradually became more coronal in the lower lumbar spine. The facet joints were also more horizontal proximally and gradually became more vertical in the lower lumbar spine except at L4 - L5 level. The facet joints at L4 - L5 were significantly more horizontal than adjacent levels. The facet tropism was statistically associated with translation at L1-L2 and L3-L4. The facet joints at L4-L5 were more horizontal than other levels, and might account for the higher incidence of degenerative spondylolisthesis at this level. Facet tropism was found to be associated with translation at L1-L2 and L3-L4 but not at the lower lumbar levels, probably because of increased degeneration of the lower lumbar spine.