Anatomic and Biomechanical Analysis of the Lower Lumbar Foraminal Ligaments

STUDY DESIGN: An anatomic cadaveric study to characterize the lumbar intraforaminal nerve root attachments. OBJECTIVES: To characterize the intraforaminal nerve root attachments and describe their anatomic relationships and biomechanical properties. SUMMARY OF BACKGROUND DATA: Observations during foraminotomies for lateral recess stenosis as well as lateral approaches for far lateral disc herniation have shown dense attachments between the nerve root and adjacent structures. Little or no information has appeared in the literature describing intraforaminal nerve root attachments. METHODS: Twelve fresh-frozen human cadaveric lumbar spines were used to study intraforaminal ligamentous structures. Four cadavers were cut into sagittal sections for qualitative description, and eight were used for biomechanical testing. Histologic analyses were performed on samples of the foraminal attachments to assure that they were not vascular or neural structures. Biomechanical testing of the nerve roots with ligamentous attachments was performed measuring load to failure along the anatomic axis of the root. RESULTS: The dissections showed four distinct bands extending radially from the nerve root sleeve. The most prominent nerve root attachment was to the facet capsule posteriorly. Other ligaments fanned out with attachments inferiorly and superiorly to the adjacent pedicles and anteriorly to the intervertebral disc. Biomechanical study of the L3, L4, and L5 nerve roots showed a significant increase in strength at failure with axial traction, progressing from L3 to L5. CONCLUSIONS: The results demonstrate that these foraminal ligaments are normal anatomic structures within the intervertebral foramen of the lumbar spine. In addition, they may play a role in limiting motion along the nerve root.