Simulation of extension, radial and ulnar deviation of the wrist with a rigid body spring model

A novel computational model of the wrist that predicts carpal bone motion was developed in order to investigate the complex kinematics of the human wrist. This rigid body spring model (RBSM) of the wrist was built using surface models of the eight carpal bones, the bases of the five metacarpal bones, and the distal parts of the ulna and radius, all obtained from computed tomography (CT) scans of a cadaver upper limb. Elastic contact conditions between the rigid bodies modeled the influence of the cartilage layers, and ligamentous structures were constructed using nonlinear, tension-only spring elements. Motion of the wrist was simulated by applying forces to the tendons of the five main wrist muscles modeled. Three wrist motions were simulated: extension, ulnar deviation and radial deviation. The model was tested and tuned by comparing the simulated displacement and orientation of the carpal bones with previously obtained CT-scans of the same cadaver arm in deviated (45 degrees ulnar and 15 degrees radial), and extended (57 degrees ) wrist positions. Simulation results for the scaphoid, lunate, capitate, hamate and triquetrum are presented here and provide credible prediction of carpal bone movement. These are the first reported results of such a model. They indicate promise that this model will assist in future wrist kinematics investigations. However, further optimization and validation are required to define and guarantee the validity of results.