Soft tissue artifact compensation using displacement dependency between anatomical landmarks and skin markers – a preliminary study

Soft tissue artifact is known to be one of the principal sources of errors using human motion analysis by means of stereophotogrammetry. As one of the ways to reduce such errors, Lucchetti, L., Cappozo, A., Cappello, A., Croce, U.D. [1998. Skin movement artefact assessment and compensation in the estimation of knee-joint kinematics. Journal of Biomechanics 31, 977–984] proposed the so-called dynamic calibration in which anatomical landmark positions are calibrated in an ad hoc motion after which they are compensated with joint angles in a motor task. However, the method was proven partially inefficient during the repetitive calculation of joint angles for anatomical landmark compensation. The present study herein attempted to offset the anatomical landmark position by using a skin marker displacement as an alternative to the compensation method with joint angles. The feasibility of the proposed method was tested by analyzing the knee motions of a patient wearing an external fixator on the shank. Its performance was later compared with the compensation method with joint angles. In the test, the proposed method was identified as effective in reducing soft tissue artifact errors by 40–80%. The errors of some of kinematic variables were significantly reduced by 25–60% compared to the compensation method with joint angles.Relevance to industryMotion analysis with stereophotogrammetry is utilized for various purposes, including clinical diagnosis, product design, and workload assessment. However, it has been known to accommodate significant errors due to the deformation of soft tissues such as those in the skin and muscles. Methods known to efficiently reduce errors due to the soft tissues are required to improve the utilization of motion analysis. The proposed method simplifies the procedure in reducing the error, and it can be implemented more easily during routine lower extremity motion analysis. But an application of this method during measurements of motions at workplaces would require a validation of the method based on scientific standards.