BACKGROUND:Studies on the tip position of the conus medullaris in a population have been limited to autopsy and long ago. Therefore, it is necessary to dynamically study the position of conus medullaris (CM) in the Chinese population by magnetic resonance imaging (MRI).OBJECTIVE: To observe the variation in position of the CM in a living population without spinal deformity through MRI. DESIGN: A controlled observation.SETTING: Qingdao Municipal Hospital.PARTICIPANTS: Totally 1199 patients who complained of low back pain and underwent MRI examination in the Department of Radiology of Qingdao Municipal Hospital between October 1993 and December 2006 were recruited in this study. The involved patients, including 765 males and 434 females, were averaged (46±14)years ranging from 5 to 85 years old. Among them, 276 patients suffered from metastatic tumor on spinal vertebrae or trauma of spinal column. Patients with scoliosis or congenital diseases of spinal cord and spinal column were rejected. Another 30 volunteers were recruited via advertisement checked up in the Department of Radiology of Qingdao Municipal Hospital.All the volunteers, including 15 males and 15 females, were averaged (32±8)years, ranging from 19 to 52 years.Written informed consents of detected items were obtained from all the subjects.METHODS: Totally 1199 patients underwent lumbar vertebra MRI scanning by a GE Signa 1.5T supraconduction MRI machine. The tip position of the conus medullaris was observed by spin echo T1 weighted and median sagittal imaging.The MRI machine was located according to its corresponding relationship with vertebral body and intervertebral disc. All the volunteers were given the dynamic research conceming the tip of CM in middle, hyperflexion and hyperextension position.MAIN OUTCOME MEASURES: Dynamic observation of the location of tip of CM in the healthy volunteers and the patients who complained of low back pain.RESULTS: The above 1199 patients who complained of low back pain and 30 healthy volunteers participated in the final analysis. ①The mean conus position of the patients who complained of low back pain was the lower third of L1 (range: middle third of T12 to upper third of L3). The variation in conus positions followed a normal distribution. The conus position in female patients was significantly lower than that of male counterparts (t =18.127,P ＜ 0.01). No significant difference in conus position was seen with increasing age (F =0.530, P ＞ 0.05). ②The tip of the CM did not change in relation to the posterior edge of vertebrae when the spine was in hyperflexion or hyperextension position.However, it got close slightly to the posterior edge of vertebrae when in hyperflexion, and got away slightly from it when in hyperextension.CONCLUSION: The location of tip of CM of our group of population ranges from the middle third of T12 to the upper third of L3, and female population have a much lower conus position than that of male ones.