A New Look at the Geometry of the Lumbar Spine

In Brief Study Design. A retrospective cohort study of the relationship between the structures that form the lumbar spine in humans. Objective. To investigate the relationship between the segmental wedging of the vertebral bodies and that of the intervertebral discs, and between the overall lordosis angle and each of the 5 lumbar segments. Summary of Background Data. Little attention has been paid to the internal relationship between the structures that form the lumbar spine. Understanding these relationships is instrumental to our ability to restore and rehabilitate the lordotic curvature. Methods. Lateral radiographs of 101 adult lumbar spines were examined in patients at spinal clinics. The patients had no history of spinal surgery and no radiographic abnormality. The radiologic parameters are the lordosis angle (LA), the body wedge angle (B), the total segmental angle (S), and the intervertebral disc angle (D). Measurements B, S, and D were taken for each of the 5 lumbar segments. Measurements B and D were used to calculate ΣB, the sum of the B, and ΣD, the sum of the D. Results. The LA correlates with the sum of the vertebral body angles and with the sum of the intervertebral disc angles. Vertebral body wedging is negatively correlated with intervertebral disc wedging. The middle 3 lumbar segments are moderately-to-poorly correlated, among themselves and with the LA, while the upper and lower lumbar segments are poorly correlated with the LA and not correlated with any lumbar segment. Conclusion. Three parts of the lumbar lordosis were identified: the upper part, formed by the first lumbar segment; the middle part, formed by the middle 3 segments; and the lower part, formed by the fifth lumbar segment. The statistical study shows an inverse relationship between vertebral body and intervertebral disc wedging. Understanding the geometry of the spine is instrumental to our ability to rehabilitate the lordotic curvature. We have found evidence that the lumbar spine is composed of upper, middle, and lower parts, and that the vertebral body and intervertebral disc shapes are inversely correlated.