This research focuses on the mechanical flexion response of the L3-L4 porcine vertebral joint as a multi-segmental and a uni-segmental specimen. The purpose was to determine if uni-segmental specimens are sufficient to evaluate the mechanical response of lumbar spinal specimens. Load-deformation curves were generated for three testing conditions using porcine lumbar spines: multi-segmental with posterior elements intact, multi-segmental with interspinous and supraspinous, ligaments sectioned at L2-L3 and L4-L5, and uni-segmental. Three parameters of the load-deformation curves were compared: slope of the high and low stiffness regions, and length of the laxity zone. A significant difference in the length of the laxity zone and range of motion was observed when the interspinous and supraspinous, ligaments were sectioned. The stiffness values failed to show a significant difference. These results are evidence of a change in the mechanical response in flexion when interspinous and supraspinous ligaments are sectioned at L2-L3 and L4-L5 and, therefore uni-segmental specimens are not appropriate for evaluation of lumbar spinal flexion mechanics.