10 - The Unseen Pathological Anatomy of Spinal Stenosis: The Sublaminar Ridge

Poster Board Number: 10
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Odd poster #s – first hour
Even poster #s – second hour

Abstract Body : Introduction and Objective

Spinal stenosis has become increasingly prevalent due to an aging population. The hypertrophy of the sublaminar ridge, which is the insertion point for the ligamentum flavum, may contribute to spinal stenosis and the consequent compression of spinal nerves. Surgical decompression of the nerves is only successful between 50 and 75% of the time and the reason for the failure is unclear. We hypothesize that the sublaminar ridge may play a role in these failed interventions. Despite its clinical significance, there are no formal studies on the pathological anatomy of the sublaminar ridge in the degenerated spine with only some anecdotal observations found in existing literature. This study aims to explore the anatomy of the normal and pathological lumbar sublaminar ridge in the lateral recess by qualitatively describing the structure and its relationship with the exiting nerve root.

Materials and Methods

Lumbar spinal blocks (T12 to S1) were removed from 5 soft fixed female cadavers. All soft tissue around the lumbar spine was removed apart from exiting spinal nerves. Next, the anterior and posterior columns of the spine were separated to produce an anterior view of the spinal canal and intervertebral foramina. Observations regarding the distortion or compression of the exiting nerve root as well as the orientation of sublaminar ridge in relation to the nerve root were made.

Results

The nerve root is known to exit directly under the pedicle. It often crosses the sublaminar ridge, which is inferior to the mid-pedicle and on the medial aspect of the intervertebral foramen. The displacement of the nerve root anteriorly may cause the root to be compressed against the vertebral bodies or the disc, while superior elevation of the nerve root from the sublaminar ridge may compress the root against the pedicle.

Preliminary observations indicate there is variability in shape and size of the sublaminar ridge between lumbar spine levels. The shape of the sublaminar ridge can be classified into one of four categories (Type A-D), as described in a previous study conducted by our team. Type A is characterized by horizontal ridge lines with no spikes. Type B is defined by a horizontal ridge line with spikes. Type C has spikes and a dipped end. Type D is categorized by spikes and a distally curved end.

Conclusions

Dissecting the lumbar spine allowed for the gathering of critical baseline data regarding the investigation of the lumbar sublaminar ridge in the lateral recess. Qualitative observations included variability in shape and size of the sublaminar ridge resulting in differing degrees to which the sublaminar ridge may contribute to spinal stenosis.

Significance/Implication

Exploration of the sublaminar ridge has implications in developing surgical approaches for lumbar spinal stenosis, as hypertrophy or spinal degeneration of this structure may be involved in the compression of spinal nerves in spinal stenosis. The documentation of the morphology of the sublaminar ridge and its relationship to spinal nerve roots may provide key information for surgeons during the exploration and debridement of the ridge to achieve complete and successful decompression of the nerve roots. Thus, these findings have the potential to improve patient outcomes for spinal decompression surgeries.