Morphometry of lumbar intervertebral foramen

Abstract

Background: The spinal nerve roots exit through the intervertebral foramina and the proportion between the size of the foramen and the relative space occupied by the root determines the chance of root compression in the intervertebral foramen. Not much data exists regarding the variations in the dimensions of the intervertebral foramen in Indian subjects. Methods: Twenty one sets of lumbar vertebrae dissected out from the cadavers in the Department of Anatomy, was used for the study. The vertical and transverse diameters of the intervertebral foramina were measured. The vertebral foramen index was then calculated by taking the ratio between the vertical diameter and the transverse diameter. Result: It was seen that the vertical diameter was more than the transverse diameter at all levels except at the L 5 -S 1 foramen where it was the other way round. Even though there was a difference in the foramen size between the right and the left sides, it was not statistically significant. There was decrease in the transverse diameter from L 1 (mean 9.89 mm) to L 3 levels (mean 9.78 mm) and thereafter an increase at L 4 (mean 11.15 mm). The vertical diameter showed an increase from L 1 (mean 14.83 mm) to L 2 levels (mean15.52mm) and thereafter a decrease from L 3 (mean 15.29 mm) to L 5 (mean 12.48 mm) which was not statistically significant. The antero-posterior dimension of the superior notch was less than that of the inferior notch at all levels. The vertebral foramen index showed a gradual increase from L 1 (mean 1.47) to L 3 (1.58) and thereafter a decrease at L 5 level (0.94). Conclusion: The foramen dimensions are critical in determining the foraminal constrictions of the lumbar spine. The transverse and vertical dimensions do not have a bearing on each other, as indicated by the vertebral foramen index.