Inertial and magnetic motion tracking: Anatomical calibration

Traditionally, movement analysis is performed by means of photogrammetric systems (PS). PS's are accurate, expensive and cannot be used outside the laboratory. To overcome these limitations, inertial and magnetic sensing (IMS) units can be used. Each IMS unit provides a three DOF orientation relative to a global earth-fixed frame. For an effective estimate of joint kinematics, it is necessary to define, for each bony segment involved, an anatomical frame (AF). Relevant axes may be determined as rotation axes of a segment relative to an another during ad-hoc movements occurring in an anatomical plane (functional approach). Relevant drawbacks are: movement planes are subjective and as such not repeatable, joint impairment may produce axes that are not consistently related with bone anatomy and hinder the wide rotations required for accurate axis determination. In this study a calibration approach, based on the direct identification of anatomical landmarks as normally done in photogrammetry, is presented and its performance assessed.