The Morphology of the Lumbosacral Articular Processes in Adult Chinese and Its Biomechanical Implication

Aim: The morphology of the lumbosacral intervertebral joints in the Chinese race was investigated in the present study to understand the relationship between the articular joint interface and intervertebral disc prolapses.

Methods: Spine specimens (N=30) from both male and female adults with ages ranging from 30 to 60 years old were used. They were fixed with 3% formaldehyde, frozen and cut through the intervertebral joints and the intervertebral disc. The angle between the facet joint interface and the median sagittal line on both sides was measured for each joint.

Results: The angle between the facet joint interface and the median sagittal line increased gradually from the L1-L2 joint to L5-S1 joint, and the angles in the L4-L5 and L5-S1 joints were both significantly wider than those of other lumbar intervertebral joints. When the angles on the left side were compared with those of the right side, those on the left side were significantly wider than those on the right side. Since the force acting toward the intervertebral disc can be decomposed into one component perpendicular to the facet joint interface and one parallel to the facet joint interface, when the facet joint interface is in a more sagittal position, it blocks less shearing force that acts to slide the vertebra anteriorly. When the facet joint interface is in a more coronal position, it blocks most of the force.

Conclusion: Although the L1 –S1 are more coronal in positions on the left side, most disc prolapses happen on the left side, suggesting that some adaptive processes might contribute to the more coronal orientation of these facet joint interfaces or the shearing force act more along the facet joint interface on the other side.