ABSTRACT
Accurate and precise measurements of the kinematics and kinetics of human joints are necessary to understand the normal and pathological function of the musculoskeletal system during movement performance [1-6]. Yet knowledge about joint kinematics and kinetics are limited by the accuracy of measuring system used [7]. Usually joint kinematics are obtained by attaching reflective markers to the segment on the skin. Based upon rigid body mechanics, three-dimensional kinematics assumes that markers placed on the skin represent the position of bony landmarks of the segment. However, skin markers move in relation to these bony landmarks resulting in relative errors [8]. Consequently, considerable questions remain concerning the accuracy of joint kinematics [9]. Reinschmidt et al. [10] have reported a segmental error due to skin movement artefact of approximately 5 degrees. In vivo measurements of the skeletal motion by typically using markers fixed on bone pins represent an accurate technique but ethically questionable [11-13]. This provides one of the most accurate means for determining bone movements [14]. Since in vivo and invasive methods for joint kinematics are not suitable for routine analyses, surface marker optimisation methods have been proposed to correct skin movement artefacts through the application of clusters of markers [15-17]. Some methods reported reduced kinematics errors between 25 and 33%, however, no studies have validated their techniques with in vivo kinematics data.
