Schematic drawing showing the method of measuring the glenoid scapular angle (GSA) and humeral head subluxation. The glenoid scapular angle measurement (GSA) is according to Friedman et al.  and the humeral head subluxation according to Waters et al. . For the GSA the angle in the posterior quadrant is measured and 90° are subtracted from this angle to determine glenoid version. For the subluxation the percentage of the humeral head anterior to the line from the medial margin of the scapula through the mid point of the glenoid is used. (Figure from Waters PM, Smith GR, Jaramillo D: Glenohumeral deformity secondary to brachial plexus birth palsy. J Bone Joint Surg Am 1998, 80: 668–677. Reprinted with permission from The Journal of Bone and Joint Surgery, Inc).