COMMENTARY

Does Disc Shape Determine IVD Herniations?

Joseph K. Lee, MD

Disclosures

May 10, 2010

Introduction

Intervertebral disc (IVD) herniations are commonly diagnosed on imaging studies. IVD herniations occur most commonly in the posterolateral direction. The consequences and effects of inherent IVD structure, however, have not been well delineated in the role of IVD herniations.

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

Yates JP, Giangregorio L, McGill SM
Spine .2010;35:734-739

Summary

Dr. Yates and colleagues sought to identify the role that the size and morphology of intervertebral discs play in the evolution of a disc herniation. Twenty-two porcine cervical spine specimens were placed under compressive loads and subsequently under repetitive flexion-extension cycles. A radioopaque contrast/custom blue dye mixture was injected into the discs through the anterior annulus fibrosus and subsequently evaluated via serially computed tomographic (CT) imaging, contrast-enhanced plain films.

IVD shapes ranged from ovoid to kidney-shaped (limaçon) discs. In total, 81.8% (18/22) specimens were found to have posterior or posterolateral disc herniations, 17 of which were considered to have only a partial IVD herniation on imaging, which was confirmed by gross anatomic dissection. V angles, as shown in Figure 1 were developed by the investigators to quantify the different IVD shapes.

Figure 2 illustrates that the discs with larger V angles, which correlate with more ovoid-shaped discs, tend to have a higher probability of a "directionally diffuse" IVD herniation, whereas smaller V angles (kidney-shaped discs) tend toward having a "directionally concentrated" IVD herniation.

Viewpoint

IVD herniations have long been associated with various external factors, such as body position and activity.[1,2,3,4] Studies have revealed that IVD herniations occur typically in the posterior/posterolateral direction, where the highest stresses have been shown to occur.[5,6] This study by Dr. Yates' group suggests that the inherent size and shape of an IVD play significant roles in producing areas of increased annular stress and subsequent IVD herniations that are consistent with recent studies.

Abstract

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