Lumbar Facet Orientation in Spondylolysis: A Skeletal Study

Study Design. Orientation of the lumbar articular facets at the L1–L5 level was measured and analyzed. Objective. To characterize the relationship between lumbar facet orientation and isthmic spondylolysis. Summary of Background Data. Whereas many studies have explored the relationship between facet orientation in the transverse plane and various spinal pathologies, there is insufficient data regarding this relationship and isthmic spondylolysis. Methods. A 3-dimensional digitizer was used to measure the transverse orientation of the lumbar facet joints at the L1–L5 level in 115 male individuals with bilateral isthmic spondylolysis (at L5) and 120 age and sex-matched normal control subjects from the Hamann-Todd Human Osteological Collection (Cleveland Museum of Natural History, Cleveland, OH). Statistical analysis included paired t tests and analysis of variance. Results. In both isthmic spondylolysis and control groups, considerable shifts were noticed from sagittally oriented articular facets at L1 to frontally oriented facets at L5. The change in orientation was significantly greater (up to 13° at L4) in the isthmic spondylolysis group (right inferior facets). Three of the 4 articular facets of L5 (right and left inferior and right superior) were significantly more frontally oriented in isthmic spondylolysis compared to the control group. A greater tendency of asymmetry in facet orientation was noticed in the isthmic spondylolysis group. Conclusion. Individuals with more frontally oriented facets in the lower lumbar vertebrae incorporated with facet tropism are at a greater risk for developing isthmic spondylolysis at L5.