Biomechanical Analysis of Influence of Spinal Fixation on Intervertebral Joint Force by Using Musculoskeletal Model

Abstract

Evaluation of the intervertebral joint force in vivo is very important for clinical spine problems, for example, spinal instability, disorder of intervertebral disc, compressive fracture of osteoporotic vertebra, etc. Direct measurement of the joint force is difficult to get permission, so computational method to calculate the force is expected. Spine structure is mainly constructed of many vertebrae and flexible intervertebral disks, and it is unstable by itself under standing condition. Supporting by erector muscles and ligaments keep the spine standing condition, so that loading condition of each vertebra depend on the muscle and ligament forces. Biomechanical analysis of musculoskeletal system taking into account of large number of muscle and ligament forces is necessary to determine the intervertebral joint force. Commercial software to deal with the musculoskeletal system is available nowadays, and it has been applied to clinical, ergonomic or sport biomechanics problem.Surgery of spinal fixation is frequently operated for instability or disorder of intervertebral joints. Although stability of the joints is recovered and nervous symptom related with the disorder joints is relieved, additional trouble at adjoining joints with the fixation is concerned because excessive rigidity and posture change by the fixation makes load of the adjoining joints increase. It is required to evaluate the change of adjoining joint force by the fixation, to prevent additional trouble in advance. In this study, analysis of intervertebral joint force and muscle force was performed in the case with or without spinal fixation using full body musculoskeletal model developed by the AnyBody Modeling System (AnyBody Technology). The joint and muscle forces were evaluated under various posture of flexion and extension. Then influence of the spinal fixation on the intervertebral joint force at adjoining joints with the fixation was discussed.