The Level of Conus Medullaris in 629 Healthy Japanese Individuals

The conus medullaris typically terminates at the L1 level; however, variations in its level and the factors associated with the conus medullaris level are unclear. We investigated the level of conus medullaris on magnetic resonance imaging in healthy volunteers. In total, 629 healthy adult volunteers (≥50 individuals of each sex and in each decade of age from 20 to 70) were enrolled. The level of the conus medullaris was assessed based on the T2-weighted sagittal magnetic resonance images, and factors affecting its level were investigated employing multivariate regression analysis including the participants’ background and radiographical parameters. L1 was the most common conus medullaris level. Participant height was significantly shorter in the caudally placed conus medullaris (p = 0.013). With respect to the radiographical parameters, pelvic incidence (p = 0.003), and pelvic tilt (p = 0.03) were significantly smaller in participants with a caudally placed conus medullaris. Multiple regression analysis showed that the pelvic incidence (p < 0.0001) and height (p < 0.0001) were significant factors affecting the conus medullaris level. These results indicated that the length of the spinal cord varies little among individuals and that skeletal differences affect the level of the conus medullaris.