The intersegmental and multisegmental muscles of the lumbar spine. A biomechanical model comparing lateral stabilizing potential.

The intersegmental and multisegmental musculature of the lumbar spine was studied in a biomechanical model to compare their lateral stabilizing potential. By approximating the active and passive behavior of the stretch reflex as a variable stiffness spring whose stiffness was proportional to activation, the critical muscle stiffness required for mechanical stability was calculated. The model demonstrated that the intersegmental muscles were the least efficient at laterally stabilizing the spine. At any given load, multisegmental muscles were more efficient, and their efficiency increased with the number of segments spanned. The most efficient muscles were those that originated from the pelvis, spanning the maximum number of segments. The muscular model was unstable, regardless of the muscular stiffness, when any vertebral segment was devoid of muscle. Moreover, when the load on the spine is increased, buckling can be prevented most efficiently with the pelvic muscles and least efficiently with the intersegmental muscles.