The role of spinal flexion and extension in changing nerve root compression in disc herniations

Changes in nerve root compression forces with spinal motion were measured on six freshly frozen adult cadaver spine specimens. A model was devised to represent a herniated disc at the L4-5 level. This was done using an anterior approach placing a compression-measuring device through the disc at the L4-5 level and against the L5 root. An accelerometer was used to monitor the range of motion of the spine. Because the compression device was held in a static position, the only variable was the tautness of the nerve root across the tip of the device. By simultaneously monitoring motion and force delivered at the tip of the compression meter placed at the nerve root, we were able to quantitate nerve root tension forces across the tip of the measuring device in relation to spinal motion. The force was measured with controls as well as in flexion and extension. In addition, the force was measured as traction was applied to the L5 root. The amount of compressive force and tension in the nerve root increased with flexion of the spine and decreased with extension of the spine. In conclusion, flexion of the lumbar spine increased the compressive force on the L5 root and extension decreased the compressive force on the L5 root.