The bony structure of the lumbar spine, unlike the body’s thoracic spine, lacks lateral support but is a specialized structure designed to distribute the weight of heavy loads throughout the back. It consists primarily of trabeculae, a highly vascularized cancellous bone, which is organized in a fashion to redistribute stress throughout the spine. The size of these vertebral bodies progressively increases in direct relation to the augmentation of gravitational loads from the cephalic to the caudal segments of the spine. These segments are connected with ligaments and muscular tissue to each concurring segment located above or below the bony structure.
The composition of the body’s intervertebral disc consists primarily of outer annulus fibrosis, which holds the transmitting nociceptors and proprioceptive nerve endings, and the inner nucleus pulposus. Nociception is the process whereby chemical responses to interpret pain or sensation and illicit physical reactions from the brain to the central nervous system, including basic movement. The signals are sent through peripheral neural pathways and are received by the outer annulus fibrosis, posterior longitudinal ligament, facet capsule and the associated muscle groups located in the particular segment of the spine.
The composition of the inner annulus, which holds the nucleus, provides the spinal disc with supplemental support during instances of compression. A healthy nucleus pulposus consists of the majority of the surface area of each spinal disc, supporting seven-tenths of the compression against each disc.
During the course of adolescence, bone growth balances the proportionate decrease of disc height and loading pressure shifts posteriorly. Over the course of an individual’s development, the overgrowth of bone structures and the inherent hypertrophy of facets lead to the narrowing of central canals and progressive foraminal.