Human Thoracolumbar Intervertebral Discs Exhibit Progressive Stiffening in Caudal Direction

INTRODUCTION: The human spine is an extremely complex structure, whose principal function is to transfer loads from the upper body to the lower extremities while incorporating a certain amount of flexibility for locomotion. The balance between flexibility on one side and loading support on the other side is not well understood. This is in part due to the inherent limitations of studying the loading profile of the flexible members of the spinal column in-vivo. In an effort to study the biomechanics of multi-segmental spinal columns under high compressive loads, the follower load method has been introduced [1-4]. Although, it has been studied experimentally, these in-vitro experiments are constrained by similar limitations for investigating intervertebral disc biomechanics. The objective of the current study was to investigate the effect of intervertebral disc biomechanics on the flexibility of the thoracolumbar spine in flexion and extension and axial compressive load. To investigate disc biomechanics during loading, a combinatory approach of in-vitro experimentation and numerical simulations was utilized. This specimen specific approach included sensitivity of the model to biological variability.