Comparing Uniaxial and Biaxial Strain Responses of the Porcine Annulus Fibrosus

This study compared the tensile mechanical response of porcine annulus fibrosus tissue under uniaxial and biaxial loading conditions to better reflect the multidirectional strains experienced in vivo. Two-lamella annular samples harvested from cervical intervertebral discs were subjected to equivalent strain magnitudes under both loading modes using controlled strain rates. Biaxial loading resulted in significantly higher stiffness and peak force compared to uniaxial loading, despite similar peak displacements. These findings demonstrate that annulus fibrosus tissue experiences substantially higher stress under multidirectional loading, emphasizing that uniaxial testing underestimates physiological mechanical demands and tissue injury thresholds.