A novel kinematic model for a functional spinal unit and a lumbar spine

Purpose: The aim of this paper is to present the novel model for the functional spinal unit and spine designed as a rigid mechanism and solve it with methods commonly used in robotics. Method: The structure of the intervertebral joint is analyzed with special attention paid to elements defining the displacements in the joint. The obtained mechanism is then numerically solved using a constraint equations method. Results: The input data set for the simulation is prepared using the 3D scan of the lumbar spine. The simulation results show that the intervertebral joint mechanism can satisfy the ranges of flexion, lateral bending and axial rotation as compared with literature data. It is also possible to study complex, coupled displacements of the lumbar spine segment. Conclusions: Structural analysis of the functional spinal unit with methods common in robotics can eventually lead to better understanding of stabilizing and guiding mechanisms. The proposed mechanism can be used as a reference in the study of spine guidance. It can reproduce the angular displacements of the actual functional spine unit. It is also possible to expand the model to facilitate the analysis of a lumbar spine segment.