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. 2010 Apr 1;35(7):734-9.
doi: 10.1097/BRS.0b013e3181ba3a60.

The Influence of Intervertebral Disc Shape on the Pathway of Posterior/Posterolateral Partial Herniation

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The Influence of Intervertebral Disc Shape on the Pathway of Posterior/Posterolateral Partial Herniation

Justin P Yates et al. Spine (Phila Pa 1976). .

Abstract

Study design: Basic scientific investigation employing the medical imaging techniques of contrast-enhanced plane film radiographs and computed tomography in addition to gross dissection techniques on a sample of spines.

Objective: To document the specific posterior/posterolateral pathway of mechanically-induced intervertebral disc (IVD) herniation as the result of repetitive loading and disc geometry.

Summary of background data: In vitro cadaveric and animal investigations have indicated that the posterior/posterolateral aspects of the IVD are most susceptible to damage leading to herniation, and that cyclic bending is the most potent variable influencing herniation. The IVD in horizontal cross-section ranges in shape from ovoid to limacon (kidney-shaped) which influences stress distributions. The purpose of this investigation was to determine the role of the IVDs shape and size on influencing the pathway of herniation.

Methods: Compressive loads (1472 N) in conjunction with 7000 repetitive cycles of flexion-extension were applied to 22 porcine motion segments. Computed tomography images and contrast-enhanced plane file radiographs, in addition to dissection techniques were used to evaluate the progression of herniations. A logistical regression assessed the links between endplate size and shape, and the probability of a specific herniation type (directionally diffuse or directionally concentrated).

Results: A total of 18 out of the 22 specimens exhibited detectable anular damage in the posterior/posterior lateral direction. Of the 18 specimens, 17 were partial herniations while one incurred a full herniation. IVD shape was found to be predictive of the pathway of herniation (P = 0.0329); oval IVD shapes were more likely to herniate in a directionally diffuse manner (6/18), while limacon IVDs were more likely to herniate in a directionally concentrated manner (12/18).

Conclusion: The shape of the IVD appears to be predictive of the pathway of IVD herniation.

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