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A modal approach for the soft tissue artefact
mathematical representation and compensation
Tecla Bonci, Valentina Camomilla, Raphaël Dumas, Laurence Cheze, Aurelio
Cappozzo
To cite this version:
Tecla Bonci, Valentina Camomilla, Raphaël Dumas, Laurence Cheze, Aurelio Cappozzo. A modal
ap-proach for the soft tissue artefact mathematical representation and compensation. 7th World Congress
of Biomechanics (WCB 2014), Jul 2014, Boston, MA United States. �hal-01859456�
A MODAL APPROACH FOR SOFT TISSUE ARTEFACT MATHEMATICAL REPRESENTATION
AND COMPENSATION
Bonci T.1,2, Camomilla V.1, Dumas R.2, Cheze L.2, Cappozzo A.1.
1 Department of Movement, Human and Health Sciences, Università degli Studi di Roma “Foro Italico”, Rome, Italy 2 Université de Lyon, F-69622, Lyon; IFSTTAR, LBMC, UMR_T9406, Bron; Université Lyon 1, Villeurbanne, France
INTRODUCTION
Optimal bone pose and joint kinematics estimators, that use data provided by stereophotogrammetry, aim at compensating for soft tissue artefacts (STA). We suggest that they embed a mathematical representation of the STA that adequately approximates it and uses a sustainable number of parameters. To this purpose we propose to represent STAs with a modal approach using different STA definitions: individual marker displacements (MrkD), marker-cluster geometrical transformations (GT), or skin envelope shape variations (SV) [1]. Modes can be ranked and a number of them selected leading to different degrees of approximation of the STA reconstruction and, therefore, compensation. This study investigated how, for each STA definition, the selected number of modes, the resulting STA approximation and accuracy of joint kinematics estimates relate to find the most appropriate STA mathematical representation.
MATERIALS and METHODS
Experimental data provided by Reinschmidt et al., (Journal of Biomechanics, 1997:729-732) were used. STA vectors and reference knee kinematics were determined using intracortical pin data during running trials. For each segment i, a STA field Vi(k) was generated. For each STA definition, Vi(k) was split into additive modes (amplitude ail(k) and
direction Φi l
) that were ranked. As a paradigmatic case, for each definition, a number of modes (ri) was selected that
represented the 95% of the STA deformation energy and the residual STA (5%) fields computed Ṽi(k).
Knee kinematics was calculated, through an SVD approach, using skin marker positions embedding Vi(k) (raw data:
RD) or Ṽi(k) (STA virtually compensated data) associated with each STA definition (MrkD, GT, SV). For each of the
four kinematics estimates thus obtained, the rms difference with respect to the reference kinematics was calculated (rmse).
RESULTS
DISCUSSION
The selection of a STA definition and its modal representation allows for a trade off between virtual STA compensation effectiveness and number of modes, that is number of parameters involved, and, therefore, mathematical tractability of the bone-pose estimator. The GT definition grants for the best knee kinematics estimate accuracy, but uses 6-10 modes; while the SV definition allows for a slightly worst accuracy, but uses only 2-3 modes.
KEY REFERENCE
[1] Dumas, R., Camomilla, V., Bonci, T., Cheze, L., Cappozzo, A., 2014. Generalized mathematical representation of the soft tissue artefact. Journal of Biomechanics 47,476–481
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BONCI, Tecla, CAMOMILLA, Valentina, DUMAS, Raphaël, CHEZE, Laurence, CAPPOZZO, Aurelio, 2014, A modal approach for the soft tissue artefact mathematical representation and compensation, 7th World Congress of Biomechanics, BOSTON, ETATS-UNIS, 2014-07-06, 1 p
