REGIONAL AND DIRECTIONAL DIFFERENCES OF THE INTERVERTEBRAL DISC ANNULUS FIBROSUS MECHANICAL PROPERTIES

Abstract

The loading experienced by military helicopter and fighter aircrew can lead to spinal injury by degrading the soft tissues. Fighter pilots endure low frequency high magnitude loading, while helicopter pilots endure high frequency vibrational loading over longer periods of time. The purpose of this study is to analyze intervertebral disc material properties, including elastic modulus, failure strain, and failure stress. This will provide data to model the annulus fibrosus to predict the risk of injuries. Quantifying the risk to specific spinal locations could provide insight to improve the design of protective clothing and equipment. Single layers of the porcine annulus fibrosus were subjected to tensile failure tests to determine the mechanical properties. Results showed a significantly (p< 0.05) higher elastic modulus in the circumferential direction compared to the axial direction. There was also a significantly greater elastic modulus for samples from the lateral region of the disc compared to the posterior region. There was no significant difference for the anterior region or specimen depth with regards to elastic modulus. Failure stress showed significant differences between superficial and deep specimens as circumferential and axial testing directions. Failure strain only had differences between circumferential and axial directions. This data can be used to help predict where in the disc an injury may occur. Because of the decreased posterior elastic modulus, tensile failure is more likely to occur in that region.