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Measurement of occlusion of the spinal canal and intervertebral foramen by intervertebral disc bulge

Mathieu Cuchanski, BS,1 Daniel Cook, MS,2,3 Donald M. Whiting, MD,4 Boyle C. Cheng, PhD1,2

1Department of Neuroscience, University of Pittsburgh, Pittsburgh, PA 2Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA 3Department of Neurological Surgery, University of Pittsburgh, Pittsburgh, PA 4Department of Neurosurgery, Drexel University College of Medicine, Pittsburgh, PA

Abstract 

Background

Disc protrusion has been proposed to be a possible cause of both pain and stenosis in the lower spine. No previous study has described the amount of disc occlusion of the spinal canal and intervertebral foramen that occurs under different loading conditions. The objective of this study was to quantitatively assess the percent occlusion of the spinal canal and intervertebral foramen by disc bulge under different loading conditions.

Methods

Spinal canal depth and foraminal width were measured on computed tomography–scanned images of 7 human lumbar spine specimens. In vitro disc bulge measurements were completed by use of a previously described method in which single functional spinal units were subjected to 3 separate load protocols in a spine test machine and disc bulge was recorded with an optoelectric motion system that tracked active light-emitting diodes placed on the posterior and posterolateral aspects of the intervertebral disc. Occlusion was defined as percentage of encroachment into area of interest by maximum measured disc bulge at corresponding point of interest (the spinal canal is at the posterior point; the intervertebral foramen is at the posterolateral point).

Results

The mean spinal canal depth and mean foraminal width were 19 ± 4 mm and 5 ± 2 mm, respectively. Mean spinal canal occlusion under a 250-N axial load, ± 2.5 Nm of flexion/extension, and ± 2.5 Nm of lateral bend was 2.5% ± 1.9%, 2.5% ± 1.6%, and 1.5% ± 0.8%, respectively. Mean intervertebral foramen occlusion under a 250-N axial load, ± 2.5 Nm of flexion/extension, and ± 2.5 Nm of lateral bend was 7.8% ± 4.7%, 9.5% ± 5.7%, and 11.3% ± 6.2%, respectively.

Conclusion

Percent occlusion of the spinal canal and intervertebral foramen is dependent on magnitude and direction of load. Exiting neural elements at the location of the intervertebral foramen are the most vulnerable to impingement and generation of pain.

keywords: 
Disc bulge, Spine biomechanics
Volume 5 Issue 1
doi: 
10.1016/j.esas.2010.09.004