Rade M. and Shacklock M. et al. 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. Spine: 2015
- Following the notion that the SLR tests movement and mechanosensitivity of the L4, L5, and S1 nerve roots by applying caudally directed tensile forces to the neural tissue, several researchers have investigated neural displacement in response to this maneuver
- It was therefore hypothesized that, at certain times, the conus might be directly proportional to the sliding of the L5 and S1 neural roots, consistent with the “principle of linear dependence
- Of particular interest is (1) whether the magnitude of conus medullaris displacement increases with more hip flexion, resembling more accurately the common clinical SLR and (2) whether the “principle of linear dependence” would be substantiated at greater amounts of hip flexion
- In addition, attempts will be made to improve the measurement methodology with the aid of 3-dimensional (3D) MRI scanning, so as to investigate whether the methodology itself could be improved in terms of clinical feasibility and better values with inter- and intrarater reliability testing
- The authors calculated that subjects taller than 183 cm (6 feet) were needed to allow performance of the SLR in the scanner, permitting at least 60 ° of unrestricted hip flexion
- The average displacement for the unilateral SLR was 3.54 ± 0.87 mm
- The conus displacement for bilateral SLR was 7.42 ± 2.09 mm
- Caudal displacement of the conus at 60 ° SLR was significantly greater than the authors’ previously reported results for a 50 ° SLR
- The fact that the displacement was virtually double with bilateral SLR may indicate that (1) a linear dependency between the magnitude of cord movement and number of nerve roots involved and (2) this relationship is maintained at greater angles of hip flexion
- This study provides conclusive evidence that the spinal cord displaces caudally with the lumbar nerve roots during both the clinically applied unilateral and bilateral SLRs.
- Moreover, the high correlation values presented in this study show that these medullar cone movements are significant, consistent, and reproducible