Evidence from cadavers suggestive of entrapment of fifth lumbar spinal nerves by lumbosacral ligaments.

Lumbosacral spines from 51 geriatric-age cadavers (25 men and 26 women) were examined both grossly and under the dissecting microscope for evidence of compression of fifth lumbar spinal nerves by their respective lumbosacral ligaments. These ligaments were found to extend from the transverse process and body of L5 to the ala of the sacrum in 97% of the specimens, and from the transverse process and body of L5 to the promontory of the sacrum in 3% of the specimens. Anterior primary rami of the fifth lumbar spinal nerve were observed to be compressed in 11% (11 of 102) of the specimens examined grossly and under the dissecting microscope. Histologic evidence of chronic compression, as suggested by perineurial and endoneurial fibrosis, peripheral thinning of myelin sheaths, or subjective evidence of a shift in fiber diameter to a population of smaller size fibers was found, deep to the lumbosacral ligament, in three of the 11 nerves judged to be compressed. The information derived is of interest to the clinician whose patient presents with L5 root signs and a myelogram, discogram, and computed tomographic scan which do not show any abnormality. The possibility of extraforaminal compression must be considered as a possible source of the clinical signs.