Propagation of soft tissue artifacts to the center of rotation: A model for the correction of functional calibration techniques

Abstract

This paper presents a mathematical model for the propagation of errors in body segment kinematics to the location of the center of rotation. Three functional calibration techniques, usually employed for the gleno-humeral joint, are studied: the methods based on the pivot of the instantaneous helical axis (PIHA) or the finite helical axis (PFHA), and the "symmetrical center of rotation estimation" (SCoRE). A procedure for correcting the effect of soft tissue artifacts is also proposed, based on the equations of those techniques and a model of the artifact, like the one that can be obtained by double calibration. An experiment with a mechanical analogue was performed to validate the procedure and compare the performance of each technique. The raw error (between 57 and 68 mm) was reduced by a proportion of between 1:6 and less than 1:15, depending on the artifact model and the mathematical method. The best corrections were obtained by the SCoRE method. Some recommendations about the experimental setup for functional calibration techniques and the choice of a mathematical method are derived from theoretical considerations about the formulas and the results of the experiment.

A model of the soft tissue artefact rigid component

“…Since the mode amplitudes, , can in principle be estimated together with bone pose, the proposed model architecture is appropriate for incorporation in various kinds of BPEs: single-body BPEs (Alexander and Andriacchi, 2001), multi-body BPEs (Richard et al, 2012), and algorithms based on a functional approach (de Rosario et al, 2013). The choice of embedding a model describing only the STA rigid component in a BPE is supported by the following considerations:…”

“…This is normally done using quaternions\attitude vectors and translation vector, or transformation matrices (de Rosario et al, 2013, Richard et al, 2012 that entail specific algebra and constraints (e.g., unitary quaternions, orthogonal matrices). This procedure, overly complicated from the computational point of view, can be avoided by using the modal representation, which is more convenient in optimising the BPE.…”

Surface marker cluster translation, rotation, scaling and deformation: Their contribution to soft tissue artefact and impact on knee joint kinematics

“…Furthermore, our findings concur with previous results using larger marker clusters, indicating our approach was robust. For example, Barre et al (2013) andDe Rosario et al (2013) determined that the rigid body movement (translation and rotation) of the marker cluster was larger than that of the nonrigid component. de Rosario et al (2012) also noted that the nonrigid component of the marker cluster was filtered out of the data set and, therefore, did not introduce any kinematic errors in joint kinematics, which was also the case in this study.…”

Accuracy Improvement on the Measurement of Human-Joint Angles

“…A considerable amount of work has already been devoted to the problem of improving the accuracy of measurements of joint angles of the arm [9], [10], [11], [12], [13]. These mocap systems are based on reflective markers placed on the user's arm and tracked by the infra-red (IR) cameras.…”

“…First, θ i,1 and θ i,2 are based on the difference in orientation of the sensors and marker plates, not on the difference in orientation of the sensors and bones. The orientation of the bones is estimated with the IR-camera mocap system and marker plates which are realigned with the bones at every arm position in order to minimize the effects that human tissue has on the plates' orientation [7], [9], [10], [11], [12], [13]. Second, the coordinate system of the IR-camera mocap system is referenced to the earth's gravity and magnetic north with a level and digital compass respectively.…”