Study design: Controlled radiological study.
Objective: To investigate noninvasively in vivo spinal cord displacement in the vertebral canal during the passive straight leg raise (SLR) in asymptomatic subjects. The basic assumption is that the cord follows L5 and S1 nerve roots displacement by similar magnitude and direction (principle of linear dependence).
Summary of background data: It is generally accepted that the SLR produces some caudal movement mainly of L5 and S1 nerve roots, but the magnitude of this displacement is still a matter of debate.
Methods: Sixteen asymptomatic volunteers were scanned with 1.5-T magnetic resonance scanner (Siemens Avanto, Erlangen, Germany) using T2-weighted turbo spin-echo fat-saturation sequence. The displacement of the medullar cone relative to the vertebral endplate of the adjacent vertebra during the passive SLR was quantified and compared with the position of the conus in the neutral (anatomic) position. Each movement was performed twice for evaluation of reproducibility. The measurements were repeated by 2 observers. Four practitioners performed the maneuvers in a random sequence to avoid series effects.
Results: Compared with the neutral (anatomic) position, the medullar cone displaced caudally in the spinal canal by 2.31 ± 1.2 mm with right (P ≤ 0.001) and 2.35 ± 1.2 mm with left SLR (P ≤ 0.001). Spearman correlations proved higher than 0.99 for intra and interobserver reliability, as well as results reproducibility testing for each maneuver.
Conclusion: The data show that the spinal cord in the thoracolumbar region slides distally in response to the clinically applied SLR test. The high correlation values in this study show that these movements are consistent and reproducible. Because of the neural continuum, the authors speculate that this movement might be directly proportional to the sliding of the L5 and S1 neural roots. This study offers baseline measurements on which further studies in diagnosis of lumbar disc protrusion and radiculopathy may be developed.