Abstract
PurposeThe objective of this study was to clarify the relationships among anatomical landmarks of the glenohumeral joint at different angles of abduction.MethodsFifteen volunteers (ten men, five women; mean age 29 years) were enrolled in this study. Images of externally and internally rotated positions at 45°, 90°, and 135° of abduction in the plane 30° anterior to the trunk were taken using an open magnetic resonance imaging system. Landmarks including the glenoidal long axis with its center, bicipital groove, center of the head, and humeral shaft axis were determined. Using a line set on the surface of the head in the plane parallel to the humeral axis (including the head center and bicipital groove with its parallel and perpendicular lines), the glenoid location and rotational relationships were investigated in each position.ResultsThe average angles of axial rotation were 48° ± 27° at 45º of abduction, 71° ± 20° at 90° of abduction, and 40° ± 27° at 135° of abduction. The trajectories of the glenoid center primarily extended over the anterior portion of the humeral head at 45° of abduction and over the posterior portion at 90° of abduction, while those at 135° of abduction were localized on a small upper portion of the head.ConclusionsThe glenohumeral relationships demonstrated that arm abduction might influence shoulder function through its effects on the portion of the humeral surface in contact with the glenoid during rotation and the resultant changes in the glenohumeral relationships.
Highlights
The shoulder has a wide range of motion [3, 12, 13]
The portion of the glenoid supporting the humeral head and the alignment of muscles connecting the bones drastically change within this range of motion
We investigated the glenohumeral relationship in maximum elevation and showed that the long axis of the glenoid coincided with a line set on the surface of the head in the plane parallel to the humeral axis that involved the head center and bicipital groove [10]
Summary
The shoulder has a wide range of motion [3, 12, 13]. The portion of the glenoid supporting the humeral head and the alignment of muscles connecting the bones drastically change within this range of motion. The function of the shoulder joint that involves holding and moving the arm may change or be influenced by glenohumeral positioning. The insertion of the short rotators approaches the glenoid surface, and the capsule surrounding the head tightens with arm elevation. This suggests that compared with positions in which the arm is lowered, highly elevated arm positions are more suitable for holding rather than moving the arm. We investigated the glenohumeral relationship in maximum elevation and showed that the long axis of the glenoid coincided with a line set on the surface of the head in the plane parallel to the humeral axis that involved the head center and bicipital groove [10].
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