Simulation of the human lumbar spine during stooping and squatting using a forward kinematics model

Working with human subjects to measure internal loadings of lumbar spine is difficult. Numerical modeling makes it possible to study response of spine to a variety of loading conditions. This paper reports the development of a rigid body model of spine using a forward kinematics approach. The model consists of accurate CAD representations of vertebrae interconnected by intervertebral discs providing six degrees of freedom at each joint. The vertebrae are articulated using Virtual Muscles controlled by PID controllers individually. The forward kinematics approach resolves the redundancy issues associated with other lumbar spine models which utilize inverse kinematics. The proposed model predicted similar trend for trunk rotations, compression forces and moments as described in the literature. The comparison between the proposed model and predictions from existing dynamic models showed good agreement.