ARUP; ISBN: 978-0-9562121-5-3 - CMBBE 2012 - Cardiff University

AN APPROACH FOR THE REDUCTION OF THE SOFT TISSUE
ARTIFACT BASED ON THE INTEGRATION OF RIGID BODY
KINEMATICS
1. ABSTRACT
Vicente Mata 1 , Nidal Farhat 2 , Álvaro Page 3 , Helios de Rosario 4
Recent studies on the evaluation of Soft Tissue Artifact (STA) reduction in lower extremity
kinematics show that conventional methods may make the estimation of relative angles
between adjacent body segments worse. In this study we introduce a method for the
reduction of the STA magnitude. This method is based on obtaining the position and
orientation of the rigid body from landmark trajectories by integration. Starting from the
first and second instant screw parameters – angular velocity and acceleration – calculated
conforming to rigid body conditions, the orientation was determined by integration after an
adequate transformation. Then position, velocity and acceleration for each landmark could
be obtained. The hip joint center was estimated using the functional method with a bias
compensation. To validate the method presented, a simulated model for the lower extremity
was created in MSC-ADAMS which is based on real lower extremity motion and includes
a STA of random patterns. Results show that the error in landmark positions was reduced
and the optimized trajectories of the landmarks conform to both rigid body conditions and
the velocities and accelerations.
2. INTRODUCTION
It is well known that the kinematic and dynamic analysis of a lower limp is greatly affected
by the STA (Benoit et al. 2006; Tsai et al. 2011). Traditional methods were based on
constraining the movement/trajectory of the measured landmarks in an optimization
process, to correspond to rigid body with additional constraints for joints between adjacent
bodies, as in, for example (Cerveri et al. 2005; Andersen et al. 2009). This method, as
concluded by (Andersen et al. 2010), does not reduce the error due to soft tissue artifacts.
On the contrary, errors in the main joint angles, flexion/extension and abduction/adduction
were increased in many trials, (Andersen et al. 2010).
Moreover, in the optimization process, as both rigid body conditions and joint constraints
are cast in the same process, errors may be badly distributed between these parameters.
This method also dismisses a lot of research into the estimation of joint parameters from the
1
Professor, Centro de Investigación de Tecnología de Vehículos, Universitat Politècnica de València, Camino
de Vera s/n, 46022 Valencia, Spain.
2
Assistant professor, Centro de Investigación de Tecnología de Vehículos, Universitat Politècnica de
València, Camino de Vera s/n, 46022 Valencia, Spain.
3
Professor, Instituto de Biomecánica de Valencia, Universitat Politècnica de València, Camino de Vera, s/n,
46022 Valencia, Spain.
4
Researcher, Instituto de Biomecánica de Valencia, Universitat Politècnica de València, Camino de Vera, s/n,
46022 Valencia, Spain.