Modular Components for Detailed Kinematic Modelling of Joints

Kinematic modeling of joints is an important element for proper motion analysis of tasks, including the estimation of muscle lengths and moment arms [Delp and Loan, 1995]. In general, anatomical axes of rotation and joint centres are obtained from the literature and refined to produce improved fidelity of motion [Buford and Andersen, 2002]. Various applications will require different levels of detail of the kinematic model. This implies that the infrastructure used to model the joints should be scalable in complexity and be modular so that local regions can have their own custom models yet still co-exist within the same skeletal model. In addition, the use of mechanical joint models can result in joint degrees of freedom that may not coincide with a clinician’s or physiotherapist’s intuitive descriptions of motion. For example, elevation of the scapula (shoulder shrugging) can be specified by rotating the sterno-clavicular joint to create superior motion in the scapula. Unfortunately, the skeleton hierarchy would also propagate the rotation to the humerus, which may not be desired (Figure 1).