The effect of glenoid inclination on superior humeral head migration.

Superior humeral head migration may contribute to the development of rotator cuff disease. The purpose of this study was to test the hypothesis that superior inclination of the glenoid facilitates superior humeral head migration. Eight cadaveric shoulders were tested by use of a custom test fixture, and rotator cuff forces were applied. Glenoid inclination was varied (intact, +5 degrees, +10 degrees, and +15 degrees ), and the force required to produce superior humeral head migration was measured. Each increase in glenoid inclination (more superiorly facing glenoid) produced significant reduction in the force required for superior humeral head migration (5 degrees, 14.2% reduction; 10 degrees, 29.9% reduction; and 15 degrees, 37.5% reduction; P <.001). These findings demonstrate that glenoid inclination is an important factor in determining the force required for superior humeral head migration. This suggests that a more upward-facing glenoid increases the risk for superior humeral translation and, in turn, may play a role in the development of rotator cuff disease.