Figure 3.

A line is drawn from the anterior rim of the glenoid to the posterior rim. A perpendicular line is drawn bisecting the glenoid line. A circle is drawn and fit to the humeral head. A line (AC) is drawn as a diameter through the circle and parallel to the glenoid line. Point B is the intersection of line AC and the perpendicular bisector of the glenoid line. The ratio lines BC/AC in a centered humeral head is 0.5. The percent decentering was calculated as (BC/AC − 0.5) × 100%. In this example, there is 12% posterior decentering preoperatively (A). Postoperatively (B), with placement of the eccentricity of the humeral head prosthesis anteriorly, there is <0.2% decentering.