Impact of static postures on scaling accuracy of shoulder complex: Motion analysis and simulation study

• Published in: Gait & posture Vol. 106; pp. S360 - S362
• Main Authors: Sheikhinia, Setareh, Raoufinia, Mohammad Reza, Shamsi, ShervinDokht, Asadollahi, Setayesh, Ghaderyzadeh, Rozhina, Valadbeigi, Saba, Pour, Rahim Barjaste Kafi, Akbari, Zahra, Barnamehei, Mahdi, Mohammadi, Meroeh
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.09.2023
• ISSN: 0966-6362; 1879-2219
• DOI: 10.1016/j.gaitpost.2023.07.161

The scaling is an important step of musculoskeletal modeling which alters the anthropometry of a model so that it matches a particular subject as closely as possible [1–3]. Scaling is typically performed by comparing experimental marker data to virtual markers placed on a model [4]. In order to scale the generic model marker data of static posture was used [5–7]. The common static posture for scaling and marker registration is anatomical posture, although many postures were used to create the scaled model in recent years [8]. Although, there is no strong recommendation to choose static posture for scaling the shoulder complex [9–13]. Therefore, the aim of the current study was to compare two common static postures (anatomical and abducted arm postures). Which static postures (anatomical or abducted arm) are better for scaling the shoulder musculoskeletal models? Sixteen subjects (64.3±5.5kg, 171±8.1cm, 27.5±6.5 years) participated in this study. Ten Vicon motion captures (Vicon MX, Oxford, UK, 200Hz) were used to record the surface marker trajectories [14–17]. Four musculoskeletal models in OpenSim were used: (M1) a model with only three rotational DOFs between humerus and trunk (GHJ), (M2) a model with three rotational DOFs for STJ, ACJ, and GHJ, (M3) a model with coupled motions for scapula, clavicle, and humerus, (M4) a model with an ellipsoid mobilizer for the SternoClavicular Joint [15,18]. The generic model was scaled by markers data in the two static positions: (a) anatomical posture and (b) abducted arm posture. The inverse kinematics was used to estimate kinematics variables during the abduction/adduction, axial rotation, and extension/flexion movements [19]. The marker error was applied as indicators. The primary assumption was that the advantaged posture would result in the lowest marker error. Fig. 1 presents the mean and standard deviation of marker error of scaling procedure of two static postures (anatomical and abducted arm) for four different musculoskeletal models of the shoulder. Anatomical posture shows higher marker error for all models compared to abducted arm posture. Significant differences between the two postures observed for all models except model M4. [Display omitted] Fig. 1: Mean and standard deviation of marker error of scaling procedure of two static postures (anatomical and abducted arm) for four different musculoskeletal model of shoulder. This study aimed to compare two common static postures (anatomical and abducted arm) to find which posture is better for scaling the shoulder models. According to results, abducted arm posture had lower marker error for all models. Therefore, the abducted arm posture is a better posture to scaling the shoulder musculoskeletal models.