1. The relative amounts of scapular (S) and glenohumeral (GH) movements have beets insvestigated roentgenographically, using sixty-one male subjects each with the arm in five positions of abduction in the scapular plane.
2. The five positions of abduction studied yielded a number of interesting points. Of special interest is the fact that, in the rest position, the glenoid cavity of the scapula faces somewhat inferiorly in over 80 per cent of the individuals, the mean downward inclination for the series being slightly over 5 degrees.
3. The mean total scapular rotation was 65 degrees and the mean total glenohumeral movement, 103 degrees. The percentages of subjects reaching different maximum amounts of abduction have been recorded.
4. A regression line for predicting glenohumeral angle (Y) from arm angle (X) was calculated (Y = 3.941 + 0.605 X), which indicates that, during abduction in the scapular plane, for every 2 degrees of scapular rotation, there are, on the average, 3 degrees of glenohumeral movement.
5. The linearity of this relationship could not be rejected at the 5 per cent level of acceptance, and this implies that the ratio is constant for the whole movement. However, when the full movement was analyzed in four phases, a higher GH/S ratio was found in the final phase, indicating a relative increase of glenohumeral motion as the final stage of abductions is reached.
6. The 95 per cent probability interval calculated for the observations (+/- 15 degrees) indicates a considerable amount of individual variation in the movements.
Copyright 1966 by The Journal of Bone and Joint Surgery, Incorporated