Mathematical Modeling of Normal, Degenerated, and Fused Cervical Spines Using IAR’S Concept

During flexion/extension, of the head-neck system, cervical spine undergoes a stepwise motion from the upper to lower regions with a specific time lag. Motion of each vertebrae is composed of a translation and a rotation with respect to lower vertebrae, which may be considered as an absolute rotation about an axis called Instantaneous Axis of Rotation (IAR). Location of this axis is different between normal, and degenerated spines. In this research intersegmental force-moments are evaluated and compared in normal, degenerated, and fused subjects employing a biomechanical model of head-neck system based on IAR’s concept and the results are presented.