Elsevier

Journal of Biomechanics

Volume 62, 6 September 2017, Pages 39-46
Journal of Biomechanics

Main component of soft tissue artifact of the upper-limbs with respect to different functional, daily life and sports movements

https://doi.org/10.1016/j.jbiomech.2016.10.019Get rights and content

Abstract

Soft tissue artifact (STA) is the main source of error in kinematic estimation of human movements based on skin markers. Our objective was to determine the components of marker displacements that best describe STA of the shoulder and arm (i.e. clavicle, scapula and humerus). Four participants performed arm flexion and rotation, a daily-life and a sports movement. Three pins with reflective markers were inserted into the clavicle, scapula and humerus. In addition, up to seven skin markers were stuck on each segment. STA was described with a modal approach: individual marker displacements or marker-cluster (i.e. translations, rotations, homotheties and stretches) relative to the local segment coordinate system defined by markers secured to the pins. The modes were then ranked according to the percentage of total STA energy that they explained. Both individual skin marker displacements and marker-cluster geometrical transformations were task-, location-, segment- and subject-specific. However, 85% of the total STA energy was systematically explained by the rigid transformations (i.e. translations and rotations of the marker-cluster). In conclusion, large joint dislocations and limited efficiency of least squares bone pose estimators are expected for the computation of upper limb joint kinematics from skin markers. Future developments shall consider the rigid transformations of marker-clusters in the implementation of an STA model to reduce its effects on kinematics estimation.

Introduction

The assessment of human body kinematics is essential in many research fields such as orthopedics, ergonomics and sport biomechanics. Accuracy of the skeleton pose estimate is dependent of the methods used to record body kinematics. Usually, trajectories of reflective markers stuck on the skin are recorded using stereophotogrammetry. Nevertheless, skin marker trajectories are affected by the soft tissue artifact (STA) defined as the relative movement between each skin marker and its underlying bone (Leardini et al., 2005, Peters et al., 2010). Since STA representations vary among literature, Dumas et al. (2014a) have proposed a generalized mathematical representation of the STA: individual marker displacements, marker-cluster geometrical transformations and skin envelope shape variations. Among these three representations, STA are more usually described either by individual marker displacements or marker-cluster geometrical transformations (Alexander and Andriacchi, 2001, Andriacchi et al., 1998, Benoit et al., 2015, Dumas and Cheze, 2009).

The ultimate purpose of STA assessment is to implement methods in order to improve kinematics estimation. These methods can be used either to define mathematical models that can be embedded in optimal bone pose estimator (Alexander and Andriacchi, 2001, Bonci et al., 2014, Camomilla et al., 2015, Camomilla et al., 2013), to implement functional algorithms for locating joint rotation center (De Rosario et al., 2013) or to assess the dynamic effects of the wobbling mass (Bélaise et al., 2016, Thouze et al., 2015). As STA may not be defined a priori because they are subject-, task- and segment-specific, a calibration (i.e. identification of the components that define the STA and of the parameters that model these components) is necessary for each studied movement. Consequently, some studies aimed at describing the components, among individual marker displacements or marker-cluster geometrical transformations that best describe STA. These studies have been performed exclusively concerning the lower-limb STA. Briefly, these investigations pointed out which skin markers located on the thigh and shank were the most subject to the STA (Akbarshahi et al., 2010, Dumas et al., 2014b, Kuo et al., 2011, Tsai et al., 2011). In addition, it was observed that STA of the lower limbs were mainly explained by rigid transformations (i.e. translations and rotations) and in a less manner by deformations (i.e. homotheties and stretches) of the marker-cluster (Andersen et al., 2012, Barre et al., 2015, Barre et al., 2013, Benoit et al., 2015, Benoit et al., 2006, de Rosario et al., 2012, Dumas et al., 2014b, Grimpampi et al., 2014). Although many studies give either qualitative or quantitative information about STA for the lower limbs, no data is available in the literature concerning the characterization of the STA for the upper-limb.

The objective of this study was to describe the main components that best represent the STA of the shoulder complex and arm during functional arm movements and daily-life or sports movements. Firstly, the description of the displacement of the individual skin markers was analyzed. Secondly, special consideration was given to the analysis of marker-cluster geometrical transformations. To that purpose, the trajectories of the skin markers relative to the bone were computed using reflective markers secured to intra-cortical pins. As STA has been shown to be task-specific, the analysis focused on movements with different amplitudes, degrees of freedom and velocities. To that aim, arm flexions and rotations as well as hair combing and hockey shooting were investigated. According the studies about the STA of the lower limb, it was hypothesized, that the STA energy was task-, location- segment- and subject-specific, while the rigid transformations of the marker-cluster explained the main part of the STA energy.

Section snippets

Participants

The raw data obtained by Dal Maso et al. (2014) have been used in this study. Four healthy male participants (age ranged between 27 and 41 years, mass ranged between 57 and 115 kg, height ranged between 1.65 and 1.82 m) volunteered to participate in this study. They signed an informed consent which was approved by the Karolinska Institute (Sweden) and the University of Montreal (Canada) ethics committees. None of the participants presented current or previous shoulder injuries.

Instrumentation

Four or five

Results

First of all, as the pin inserted into the scapula rotated a few degrees for two participants, the data concerning the scapula were given for only two remaining participants. The joint angles of each movement computed with the pin markers were presented in Fig. 2. The durations of the movements were 3.63±1.16 s, 1.57±0.31 s, 1.34±0.45 s and 0.94±0.54 s for the arm flexion/extension, arm rotation, combing mimic and hockey shooting mimic respectively.

Discussion

The purpose of this study was to describe the main components that best describe the STA of the shoulder complex and arm during functional arm movements and daily-life or sports movements. To that aim, the percentage of the total STA energy explained either by individual marker displacements or marker-cluster geometrical transformations was computed. Our hypotheses were confirmed since we firstly observed that the individual marker displacements were task- location- and subject-specific.

Conclusion

Although some studies (Begon et al., 2015, Hamming et al., 2012) assessed the effect of STA on shoulder and upper limb kinematics, to our knowledge, our study was the first one to describe the STA of the shoulder complex (clavicle, scapula and humerus) and may be a benchmark of larger scale study. Our study was performed in a modelling perspective. STA was found task-, location- and subject-specific when analyzing the individual skin marker displacements. Consequently considering individual

Conflict of interest

None of the authors are in conflict of interest with regards to this research.

Acknowledgement

This work was partially funded by NSERC, Canada discovery (#RGPIN-2014-03912) grant. The first author is scholar of the Méditis program (NSERC, CREATE).

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