123 - Visualizing the Complex Anatomy of the Sublaminar Ridge Through 3D Reconstruction

Poster Board Number: 123
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Abstract Body : Study Introduction and Objective

The sublaminar ridge (SLR), the point of insertion for the ligamentum flavum, has not been well described in the literature and is essentially invisible without radiologic imaging. Hypertrophy of the SLR and the attached flavum appears to constrict the lateral recess of the spine and may be the cause of nerve entrapment. This study aims to formulate a methodology for visualizing and measuring the SLR in both 3D and 2D rendered forms.

Materials and Methods

Lumbar spinal blocks (T12 to S1) were dissected from 5 soft-fixed female cadavers. CT scans were taken using a slice thickness of 0.625 mm and a pitch of 0.516:1. Low pitch and thin slices were prioritized to optimize image quality. Measurements of the SLR and the extent of stenosis were performed using 2D sagittal reformations on Revolution CT ES (General Electric) and 3D reconstructions on Amira (Version 6.3, Thermofisher Scientific) following reconstruction.

Using both 2D and 3D images, the height of the SLR was defined as the orthogonal distance between the most anterior point of the SLR and the lamina. To determine the extent of stenosis, the distance between the apex of the sublaminar ridge and posterior aspect of the vertebral body and the horizontal distance between the lamina and posterior aspect of the body were measured.

Results

Preliminary 2D measurements show large variability in the height of the SLR and the extent of stenosis between, and within, levels of the spine. SLR height ranged from 1.9 mm to 5.6 mm. 2D measurements of spinal stenosis revealed that protrusion of the SLR occupies 18% to 38% of the width of the intervertebral foramen, through which exiting spinal nerve roots pass.

Measurements of 3D reconstructed spines indicated the height of the SLR ranged from 2.91 to 5.61 mm. Measurement of spinal stenosis revealed that the protrusion of the sublaminar ridge occupies 21% to 45% of the width of the intervertebral foramen.

Conclusions

3D reconstruction using both Amira and GE software allowed for visualization of the SLR. Quantitative observations revealed various shapes and sizes of the SLR. Challenges with consistent measurements between the two software, 2D and 3D modalities, and between data collectors call for a more standardized approach to identifying and measuring the SLR.

Significance/Implications

Systematic study of the SLR has emphasized the high variability of the SLR and the possibility of its significant contributions to spinal stenosis and nerve entrapment. Imaging is the first line of diagnosis of spinal stenosis, thus, CT scan correlates of pathological SLR anatomy may be a useful tool in the preoperative evaluation of spinal stenosis patients and in the workup of cases where surgery has been clinically unsuccessful. Better understanding of the SLR, CT scan renderings of the SLR, as well as the reconstruction protocol may help to educate surgeons for safer operations and a higher success rate, preventing complications and deaths.

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