The orientation of laminae and facet joints in the lower lumbar spine.

The relationship between the angulation of the facet joints and that of the caudad parts of the corresponding laminae in the transverse plane was investigated with computed tomography (CT) at the vertebral levels L3-L4, L4-L5, and L5-S1. At the level of L3-L4, both the facet joints and the caudad portions of the laminae tend toward a sagittal orientation, while at L5-S1 this is more toward the frontal plane. At the level of L4-L5, they occupy an intermediate position. A highly significant correlation between the orientation of these structures is demonstrated. The caudad parts of the laminae may be considered buttresses for the inferior articular processes of the same vertebra.