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Part 3: Developing Methods of In Vivo MRI Measurement of Spinal Cord Displacement in the Thoracolumbar Region of Asymptomatic Subjects With Unilateral and Bilateral Straight Leg Raise Tests

Study Design. Controlled radiological study. Objective. Verify (1) whether conus medullaris displacement varies with the range of hip flexion and (2) whether the acquired data support the “principle of linear dependence.” Summary of Background Data. We have previously quantified normal displacement of the conus with unilateral and bilateral straight leg raise (SLR) and have described the “principle of linear dependence.” However, we have since effected methodological advances that have produced data that surpass previous studies. Methods. Ten asymptomatic volunteers were scanned with a 1.5-T magnetic resonance scanner using T2-weighted spc 3-dimensional scanning sequences and a device that permits greater ranges of SLR. Displacement of the conus medullaris during the unilateral and bilateral SLRs was quantified reliably with a randomized procedure. Results. Pearson correlations were higher than 0.99 for both intra- and interobserver reliability and the observed power was 1 for each tested maneuver. The conus displaced caudally in the spinal canal by 3.54 ± 0.87 mm (&mgr; ± SD) with unilateral (P ⩽ 0.001) and 7.42 ± 2.09 mm with bilateral SLR (P ⩽ 0.001). Conclusion. To the authors' knowledge, these are the first data on noninvasive, in vivo, normative measurement of spinal cord displacement with the SLR test at 60° of hip flexion. Conus medullaris displacement increased with hip flexion angle, while maintaining the relationship between magnitude of conus displacement and number of nerve roots involved into the movement, supporting the “principle of linear dependence.” The use of T2-weighted spc 3-dimensional sequence allows for better reliability testing, which is important for future clinical utility. Level of Evidence: 5