Quantifying the Effects of Humeral Elevation Angle, Plane of Elevation, and Motion Phase on 3D Shoulder Kinematics during Dynamic Humeral Movement in Multiple Vertical Planes

Abstract

A thorough understanding of typical shoulder motion is desirable for both clinicians and shoulder researchers. With this knowledge, comparisons between normal and special populations (e.g. athletic, working, elderly, injured) are enabled and injury mechanisms for heightened or diminished performance may be identified. The purpose of this study was to generate a robust quantification of typical shoulder kinematic profiles during dynamic humeral elevation in six vertical movement planes, and to determine the influence of humeral movement plane, movement phase, gender, and humeral elevation angle on typical scapulothoracic (ST), glenohumeral (GH), acromioclavicular (AC), and sternoclavicular (SC) kinematics. Upper limb kinematic data were collected on 15 males and 14 females as they elevated and lowered their right humerus in six vertical movement planes with elbows fully extended. A total of 60 shoulder kinematic profiles were generated for both raising and lowering motion phases. Trial-to-trial repeatability of the measured rotations, as indicated by intra-class correlation coefficient was found to be moderate (0.658) to high (0.999). Overall, as the humerus was elevated, scapulothoracic (ST) upward rotation, ST posterior tilt, sternoclavicular (SC) elevation, SC retraction, acromioclavicular (AC) elevation and glenohumeral (GH) elevation all increased. However, ST protraction/retraction, GH internal/external rotation, GH anterior/posterior plane of elevation, and AC protraction/retraction responses were less consistent. There was a main effect of humeral movement plane and elevation angle (p < 0.001) identified for all measured joint rotations. A significant phase main effect was not found for right glenohumeral +anterior/-posterior plane of elevation (GAP), glenohumeral +medial/-lateral elevation (GLE), and acromioclavicular protraction/retraction (APR). At least one significant interaction of the main effects, including that of gender, was present for all rotations. The typical shoulder kinematic profiles provided in this investigation is the largest to date of its kind obtained using skin-mounted shoulder tracking techniques. Clinical scientists will find the profiles useful because they provide motion trends that can be compared to profiles from other segments of the population, including patients with specific shoulder injuries. This work supports the more ambitious future clinical goal of being able to identify people who are at risk for developing shoulder pathologies in clinical settings in a non-invasive manner.