Lumbar extraforaminal ligaments act as a traction relief and prevent spinal nerve compression

In a previous study, ligaments that connect the extraforaminal lumbar spinal nerves with the fibrous capsule of the facet joints and the dorsolateral side of the intervertebral disc were described. This anatomical configuration suggests a mechanical role in transferring extraforaminal spinal nerve traction.

One embalmed human lumbar spine was dissected from the twelfth thoracic vertebra to the first sacral vertebra to isolate the twelfth thoracic to the fourth lumbar spinal nerves. The spinal nerves from L1 to L4 were pulled at different angles with respect to the axis of the spine. Forces of 1-6N were applied. The displacements of reflective markers glued to the proximal and distal ends of the adjoining ligaments were recorded with a video system.

The spinal nerve proximal of the extraforaminal ligaments stays centred in the intervertebral foramen when pulling at an angle. At levels L1-L4 strain reduction by the extraforaminal ligaments was largest when pulling at a wider angle to the spinal axis in the sagittal plane. Proximal to the extraforaminal ligaments less displacement was seen compared to the displacement distal of the extraforaminal ligaments when pulling in longitudinal direction. A graded decrease in the displacement proximal to the extraforaminal ligaments was seen from the levels L1-L4.

Extraforaminal ligaments play an important role in the prevention of damage due to spinal nerve traction. The proximal attachments secure a spinal nerve position central in the intervertebral foramen and also reduce longitudinal tension.