The ligamento-muscular stabilizing system of the spine

Study Design. Electrical and mechanical stimulation of the lumbar supraspin ous ligament of three patients with L4-L5 spinal deficits and of the feline model, respectively, was applied while recording electromyography on the m ultifidus muscles. Objectives. To determine if mechanoreceptors in the human spine can reflexi vely recruit muscle force to stabilize the lumbar spine, and to demonstrate , in the feline mode., that such ligamento-muscular synergy is elicited by mechanical deformation of the lumbar supraspinous ligament (and possibly of other spinal ligaments), the facet joint capsule, and the disc. Summary of Background Data. the literature repeatedly confirms that ligamen ts have only a minor mechanical role in maintaining spine stability, and th at muscular co-contraction of anterior and posterior muscles is the major s tabilizing mechanism of the spine. The literature also points out that vari ous sensory receptors are present in spinal ligaments, and that the ligamen ts are innervated by spinal and autonomic nerves. Data that describe how li gaments and muscles interact to provide stability to the spine were not fou nd. Methods. The supraspinous ligament at L2-L3 and L3-L4 was electrically stim ulated in three patients undergoing surgery to correct deficits at L4-L5. E lectromyography was performed from the multifidus muscles at L2-L3 and L3-L 4, bilaterally. In 12 cats, the supraspinous ligaments from L1-L2 to L6-L7 were mechanicall y deformed sequentially, while electromyography was performed from the mult ifidus muscles of the six levels. Loading of the ligament was applied befor e and after each of the two vertebrae were externally fixed to prevent moti on. Results. Electromyograms were recorded from the multifidus muscles, bilater ally, in the two of the three patients, demonstrating a direct relationship to receptors in the supraspinous ligament. Electromyograms were recorded f rom the feline multifidus muscle with mechanical loading of the supraspinal ligament at each of the L1-L2 to L6-L7 motion segments. In the free-spine condition the largest electromyographic discharge was present in the level of ligament deformation, and lower electromyographic discharge was recorded in two rostral and caudal segments. After immobilizing any two vertebrae, loading of the ligament resulted in electromyographic discharge in the musc les of the same level and at least one level above and/or below. Conclusions. Deformation or stress in the supraspinous ligament, and possib ly in other spinal ligaments, recruits multifidus muscle force to stiffen o ne to three lumbar motion segments and prevent instability. Strong muscular activity is seen when loads that can cause permanent damage to the ligamen t are applied, indicating that spastic muscle activity and possibly pain ca n be caused by ligament overloading.