title: A model of the soft tissue artefact rigid component.
abstract: When using stereophotogrammetry and skin-markers, the reconstruction of skeletal movement is affected by soft-tissue artefact (STA). This may be described by considering a marker-cluster as a deformable shape undergoing a geometric transformation formed by a non-rigid (change in size and shape) and a rigid component (translation and rotation displacements). A modal decomposition of the STA, relative to an appropriately identified basis, allows the separation of these components. This study proposes a mathematical model of the STA that embeds only its rigid component and estimates the relevant six mode amplitudes as linear functions of selected proximal and distal joint rotations during the analysed task. This model was successfully calibrated for thigh and shank using simultaneously recorded pin- and skin-marker data of running volunteers. The root mean square difference between measured and model-estimated STA rigid component was 1.1(0.8)mm (median (inter-quartile range) over 3 subjects × 5 trials × 33 markers coordinates), and it was mostly due to the wobbling not included in the model. Knee joint kinematics was estimated using reference pin-marker data and skin-marker data, both raw and compensated with the model-estimated STA. STA compensation decreased inaccuracy on average from 6% to 1% for flexion/extension, from 43% to 18% for the other two rotations, and from 69% to 25% for the linear displacements. Thus, the proposed mathematical model provides an STA estimate which can be effectively used within optimal bone pose and joint kinematics estimators for artefact compensation, and for simulations aimed at their comparative assessments.
authors.affiliation: Department of Movement, Human and Health Sciences, Università degli Studi di Roma ''Foro Italico'', Rome, Italy; Interuniversity Centre of Bioengineering of the Human Neuromusculoskeletal System, Università degli Studi di Roma "Foro Italico", Rome, Italy. Electronic address: valentina.camomilla@uniroma4.it.
authors.forename: V
authors.initials: V
authors.lastname: Camomilla
authors.affiliation: Department of Movement, Human and Health Sciences, Università degli Studi di Roma ''Foro Italico'', Rome, Italy; Université de Lyon, F-69622 Lyon, France; Université Claude Bernard Lyon 1, Villeurbanne, France; IFSTTAR, UMR_T9406, Laboratoire de Biomécanique et Mécanique des Chocs (LBMC), F-69675 Bron, France; Interuniversity Centre of Bioengineering of the Human Neuromusculoskeletal System, Università degli Studi di Roma "Foro Italico", Rome, Italy.
authors.forename: T
authors.initials: T
authors.lastname: Bonci
authors.affiliation: Université de Lyon, F-69622 Lyon, France; Université Claude Bernard Lyon 1, Villeurbanne, France; IFSTTAR, UMR_T9406, Laboratoire de Biomécanique et Mécanique des Chocs (LBMC), F-69675 Bron, France; Interuniversity Centre of Bioengineering of the Human Neuromusculoskeletal System, Università degli Studi di Roma "Foro Italico", Rome, Italy.
authors.forename: R
authors.initials: R
authors.lastname: Dumas
authors.affiliation: Université de Lyon, F-69622 Lyon, France; Université Claude Bernard Lyon 1, Villeurbanne, France; IFSTTAR, UMR_T9406, Laboratoire de Biomécanique et Mécanique des Chocs (LBMC), F-69675 Bron, France; Interuniversity Centre of Bioengineering of the Human Neuromusculoskeletal System, Università degli Studi di Roma "Foro Italico", Rome, Italy.
authors.forename: L
authors.initials: L
authors.lastname: Chèze
authors.affiliation: Department of Movement, Human and Health Sciences, Università degli Studi di Roma ''Foro Italico'', Rome, Italy; Interuniversity Centre of Bioengineering of the Human Neuromusculoskeletal System, Università degli Studi di Roma "Foro Italico", Rome, Italy.
authors.forename: A
authors.initials: A
authors.lastname: Cappozzo
mesh_terms: D000328:Adult; D016477:Artifacts; D001696:Biomechanical Phenomena; D001842:Bone and Bones / Q000502:physiology; D006801:Humans; D007719:Knee Joint / Q000502:physiology; D007866:Leg / Q000502:physiology; D008297:Male; D008954:Models, Biological; D009068:Movement; D010780:Photogrammetry; D012399:Rotation; D012420:Running / Q000502:physiology
keywords: Human movement analysis; Modelling; Soft tissue artefact; Soft tissue deformation; Stereophotogrammetry