Background: It has been well known that the humerus externally rotates as the arm is elevated. The restriction of humeral external rotation is observed in patients with frozen shoulder and symptomatic rotator cuff tear. The purpose of this study was to compare each angle of humeral external rotation during arm elevation in 3 plains: forward elevation (FE), scapular plain (scap), and abduction (abd).
Methods: We investigated arm elevation of 3 plains in 20 healthy males using 3-D motion analyzer. Skin markers were set up on the skin of the medial border of the scapular spine, the acromial angle, anterior and posterior of the humeral head, and the medial and lateral epicondyles. The angles of humeral external rotation (ER), which were calculated as the angle made between the scapular spine and the line from the medial epicondyle to lateral epicondyle, measured at each 10° increment of arm elevation.
Results: The arms were maximally elevated between 140° and 144° in each plain. The angles of maximum ER were 48.8° in FE, 46.6° in scap, and 44.4° in abd, and there were no significant differences. The angle of ER in abd was statistically more significant than that in FE from 10° to 40° of arm elevation. The humerus started to rotate externally at 10° of elevation in FE; however, in abd ER started at 40° of elevation.
Conclusion: There was no significant difference in the angles of ER in 3 plains of elevation, but the angle of ER during initial elevation and start of ER were different.
