Extraforaminal compression of the L5 nerve: An anatomical study with application to failed posterior decompressive procedures

This anatomical study was performed to elucidate the pertinent foraminal and lateral L5 nerve anatomy to enhance our understanding of possible neurologic causes of failed decompression surgery. Persistent extraforaminal L5 nerve compression is a possible cause of persistent symptoms following lumbosacral surgery. The amount of extraforaminal space for the L5 ventral ramus was examined in fifty adult human skeletons (100 sides). Based on morphology, the specimens were then categorized (types I-IV) on the basis of the bony space available for the nerve at this location. Next, 25 embalmed adult cadavers (50 sides) underwent bilateral dissection of the lower lateral lumbar region. The type of bony extraforaminal outlet was documented for each cadaver on the basis of our skeletal analysis. Lastly, segments (intra- and extra-foraminal) of the L5 ventral ramus were excised and examined histologically. Types I-IV outlets were found in 43, 31, 20 and 6 skeletal sides, respectively. For cadavers, 22,15, 10 and 3 sides were found to have types I-IV bony outlets, respectively. In cadavers, all type IV outlets and 70% of the type III bony configurations adjacent to the L5 ventral ramus had signs of neural irritation/injury including vascular hyalinization and increased fibrosis distal to the intervertebral foramen. No distal segments of type I and type II outlets showed histological signs of neural compromise. Patients with symptoms referable to L5 nerve compression for whom no proximal pathology is identified could warrant investigation of the more distal extraforaminal segment of this nerve.