The three-dimensional motions of glenohumeral joint under semi-loaded condition during arm abduction using vertically open MRI

Background Magnetic resonance imaging is an accurate non-invasive tool for visualizing muscles, tendons, and bones. It also provides 3D coordinate values. The purpose of the present study was to visualize and quantify the 3D positions of the glenohumeral joint during isometric abduction of the arm using vertically open magnetic resonance imaging. Methods We examined 14 shoulders of seven healthy volunteers. Magnetic resonance images were obtained in a seated position and in seven static positions of the arm from 0° to maximum abduction using vertically open magnetic resonance imaging. 3D surface models were created and 3D movements of each bone in the glenohumeral joint were calculated using a computer algorithm. We analyzed the translation and contact pattern of the glenohumeral joint. Findings In supero-inferior direction, the humeral head translated slight inferiorly from +1.9 (SD 1.0) mm at 0° to +0.8 (SD 1.8) mm at the maximum abduction. In antero-posterior direction, the humeral head translated anteriorly from 0° to 90° (mean +2.4, SD 2.6 mm) and posteriorly from 90° to 150° of abduction (mean −1.4, SD 2.7 mm). Furthermore, the humeral head had a unique contact patterns with the glenoid; the contact part of the humeral head with the glenoid changed from the central part to the posterior in the midrange of abduction. Interpretation The humeral head showed a small translation in the antero-posterior direction between 90° and 150° of abduction. In addition, the posterior part of the humeral head contacted the glenoid in this range of abduction. These findings of motion patterns in asymptomatic subjects will be necessary when comparing the kinematics with pathologic condition such as the glenohumeral instability and rotator cuff tear