Table 2 The Impingement matrix indicates the degree of extension, or combined extension/internal rotation, at which impingement occurs. The starting position is 15° abduction. From there, the humerus was extended in 5° increments to 40°. Subsequently, internal rotation was performed in this position in 5° increments. Fields with a red background indicate that impingement already occurred in the initial position of 15° abduction. Yellow fields indicate that at least a certain degree of extension was possible before impingement occurred and blue fields indicate that a certain degree of combined extension and internal rotation in extension was possible. Green fields indicate that impingement did not occur even in full internal rotation in extension

From: Computer-assisted analysis of functional internal rotation after reverse total shoulder arthroplasty: implications for component choice and orientation