Location of the extraforaminal lumbar nerve roots. An anatomic study.

Twelve cadavers were used to determine the anatomic location of the extraforaminal lumbar nerve root in the intertransverse space. After exposure of the transverse processes of the lumbar spine and the extraforaminal lumbar nerve roots, direct measurements, including the nerve root angle, nerve root diameter, distance to the superior facet, and the intertransverse space, were made bilaterally. The results showed that the extraforaminal nerve root angle and diameter and the distance between the superior facet and lateral limit of the nerve root consistently increased from cephalad to caudal. The largest dimension for height and width of the intertransverse space was found at the level of L3-4, and the smallest was found at the level of L5-S1. This information may be helpful in minimizing the incidence of injury to the lumbar nerve root during a posterolateral approach to lumbar disc.