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.

New Landmark for Localizing the Site of the Subdental Synchondrosis Remnant: Application to Discerning Pathology from Normal on Imaging.

OBJECTIVE: We hypothesized that the entry site of the basivertebral vein into the basivertebral foramen of C2 might localize the subdental synchondrosis between the odontoid process and body of C2, which may be helpful for odontoid fracture classification. METHODS: Twenty-five dry adult C2 specimens underwent thin-cut computed tomography and were sectioned sagittally. The basivertebral foramen was then correlated to internal bony anatomy. Fifty magnetic resonance images were reviewed, and the location of the subdental synchondrosis was determined. RESULTS: A basivertebral foramen was identified on the posterior surface of all dry C2 specimens. The openings were found at a distance of 30%-44% on an inferosuperior point along the vertical height of C2. For bony specimens with a subdental synchondrosis remnant (75%), entry of acupuncture needles into the basivertebral foramen was always directly at the level of the synchondrosis remnant. For magnetic resonance imaging (MRI), a subdental synchondrosis or its remnants were seen on all studies. The distance from the base of C2 to the subdental synchondrosis ranged from 9-13 mm. This equated to an inferosuperior point 32%-43% along the vertical height of C2. A strong correlation existed when comparing the location of the basivertebral foramen of bony specimens and the subdental synchondrosis location on MRI. CONCLUSIONS: The basivertebral foramen is a consistently present anatomic reference point for the subdental synchondrosis even if the latter cannot be seen on conventional radiographic imaging. Our MRI data might also be useful in helping differentiate lesions affecting C2 from normal subdental cartilaginous remnants that can be encountered on imaging.