Movements induced by straight leg raising in the lumbo-sacral roots, nerves and plexus, and in the intrapelvic section of the sciatic nerve

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Abstract
Measurements of movements induced by straight leg raising in the lumbo-sacral roots, nerves, and plexus of the sciatic nerve were made in 30 cadavers of varying ages. Points of measurement included elements of the cauda equina, the nerve in the intevertebral or sacral foramen, the lumbo-sacral cord as it passed over the ala of the sacrum and the sciatic nerve approximately 1 cm. proximal to the sciatic notch. The greatest amount of movement occurred distally in the sciatic nerve. The cauda equina was never placed under tension and the amount of movement at all points decreased with increasing age. Movement in the sciatic nerve at its exit from the pelvis began when the heel was elevated only 1-3 inches while movements at the intevertebral foramen could only be noticed when an elevation of 20-30 degrees occurred. During straight leg raising the nerve is drawn straight downwards through the notch. It then moves antero-laterally becoming tightly opposed to the underlying bone and producing a remarkable degree of pressure. Similar pressure also occurs between the lumbo-sacral cord and the ala of the sacrum. To a lesser degree pressure occurs between the nerves and vertebral pedicles at both the L4 and L5 intevertebral foramina. The density of the adhesions at the intevertebral foramina determine the fixity of the fixed point of the nerve from which downward stretch occurs. When downward movement is less, the tension in the nerve and pressure over the bony prominences are correspondingly increased. Ventro-flexion of the spine relieves root pressure without involving the sciatic nerve itself. The variable results of combined tests of flexion and straight leg raising in cases of sciatica may be due to the existence of adhesions between the nerve and bone. If patients with sciatica develop pain with these movements it may signify a sensitive nerve at the sciatic notch or at the ala of the sacrum. If no pain is induced, movement may not be transmitted to the root due to fibrous adhesions or some intrinsic lesion.