Facet Tropism - An Anatomic and CT Scan Study

Facet joint tropism is defined as asymmetry in the facet joint angles, where one joint has a more coronal orientation than the other. Facet joint tropism is currently a subject of intense interest because it has the potential to markedly alter the motion patterns of the lumbar spine and ultimately contribute to low back pain. Objective: The aim of the study was to find out the frequency of facet tropism in the adult lumbar spine. Methods: Lumbar spines from 20 cadavers of adults (18 males and 2 females) aged between 20 and 45 years were dissected. The angle of facet orientation was measured at every level using the technique of Cyron and Hutton. Similarly, available CT scans of thirty six adults between the ages of 20 and 45 years (mean 30 years) were subjected to evaluation of the lumbar spine. The facet angles were measured using digitiser and AutoCAD software. Results: This study showed that the facet tropism occurs frequently in the lumbar spine in general population especially at L4-L5, L5-S1 and L2-L3 levels. There was also a relatively high incidence of facet asymmetry at L2-L3 level in both the cadaveric and the CT Scan study. Conclusion: Facet asymmetry is common at L4-L5, L5-S1 and L2-L3 levels. Advances in Knowledge: Since the lower two lumbar levels are the most mobile segments of the lumbar spine, it is possible that any abnormal geometry of the facet joints could play a part in the pathogenesis of lumbar spinal instability and disc degeneration at these levels.