Abstract
Shoulder motions consist of a composite movement of three joints and one pseudo-joint, which together dictate the humerothoracic motion. The purpose of this work was to quantify the location of the centre of rotation (CoR) of the shoulder complex as a whole. Dynamic motion of 12 participants was recorded using optical motion tracking during coronal, scapular and sagittal plane elevation. The instantaneous CoR was found for each angle of elevation using helical axes projected onto the three planes of motion. The location of an average CoR for each plane was evaluated using digitised and anthropometric measures for normalisation. When conducting motion in the coronal, scapular, and sagittal planes, respectively, the coefficients for locating the CoRs of the shoulder complex are −61%, −61%, and −65% of the anterior–posterior dimension – the vector between the midpoint of the incisura jugularis and the xiphoid process and the midpoint of the seventh cervical vertebra and the eighth thoracic vertebra; 0%, −1%, and −2% of the superior–inferior dimension – the vector between the midpoint of the acromioclavicular joints and the midpoint of the anterior superior iliac spines; and 57%, 57%, and 78% of the medial–lateral dimension −0.129 times the height of the participant. Knowing the location of the CoR of the shoulder complex as a whole enables improved participant positioning for evaluation and rehabilitation activities that involve movement of the hand with a fixed radius, such as those that employ isokinetic dynamometers.
Highlights
The shoulder complex consists of four joints that act together to enable its full range of motion (RoM)
Other groups have examined scapular kinematics in isolation (Matsuki et al, 2011) and the scapulohumeral rhythm (Yoshizaki et al, 2009), but none have quantified the location of the centre of rotation (CoR) of the entire shoulder complex
Additional markers were placed on the shoulders and hands, providing participants with visual feedback from the motion capture system to assist them in performing each planar movement
Summary
The shoulder complex consists of four joints (glenohumeral, acromioclavicular, sternoclavicular, and scapulothoracic) that act together to enable its full range of motion (RoM). Other groups have examined scapular kinematics in isolation (Matsuki et al, 2011) and the scapulohumeral rhythm (Yoshizaki et al, 2009), but none have quantified the location of the centre of rotation (CoR) of the entire shoulder complex. The position of the joint CoR is important when considering subject positioning for evaluation and rehabilitation activities. Prior studies reported on the difficulty of aligning subjects due to the unknown location of the shoulder complex CoR relative to the thorax (Shklar and Dvir, 1995). Determining its location would facilitate more effective evaluation of the strength of the shoulder complex and improved positioning for rehabilitation. The aim of this work was to quantify the location of the CoR of the complete shoulder complex relative to the thorax
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