THE VARIATION OF POSITION OF THE CONUS MEDULLARIS IN AN ADULT-POPULATION - A MAGNETIC-RESONANCE-IMAGING STUDY

Study Design. Sequential study of magnetic resonance images of the lum bar spine. Objectives. To determine the variation in position of the c onus medullaris in a living adult population without spinal deformity. Summary of Background Data. Cadaveric studies have shown that the pos ition of the conus medullaris in the adult most commonly is located at L1-L2. There have been several studies documenting the changing level of the conus throughout infancy and childhood, but there is no detail ed study that documents the range of conus positions in a living adult population without spinal deformity. Methods. The T1-weighted, midlin e, sagittal, spin-echo magnetic resonance imaging studies of 504 patie nts were assessed to identify the tip of the conus medullaris. This lo cation was recorded in relation to the upper, middle, or lower third o f the adjacent vertebral body or the adjacent intervertebral disc. Res ults. The study group consisted of 231 men and 273 women with a mean a ge 46 years (range, 16-85 years). Most patients were being examined fo r low back pain. Patients with spinal deformity were excluded. The mea n conus position was the lower third of L1 (range, middle third of T12 to upper third of L3). The variation in conus positions followed a no rmal distribution. No significant difference in conus position was see n between male and female patients or with increasing age. Conclusions . The distribution of conus location in a large adult population was s hown to range from the middle third of T12 to the upper third of L3.