Background: In shoulders with multidirectional instability, translation of the humeral head on the glenoid is increased in the midrange because of the following three reasons: the increased retroversion, a hypoplastic posteroinferior rim, and decreased scapular abduction during arm elevation. This study aimed to clarify the relationship between glenoid inclination and glenohumeral joint stability.
Methods: Nine fresh-frozen cadaveric shoulders were tested. With a 50-N compressive load, the translation force was measured in the 3-o'clock, 6-o'clock, 9-o'clock, and 12-o'clock directions by using a tilt of 0 degrees , 5 degrees , 10 degrees , 15 degrees , and 20 degrees . When the glenoid was tilted in one direction, the translation force was measured in the direction of inclination and in the opposite direction. The stability ratio was then calculated.
Results: The stability ratio in the 3-o'clock direction significantly decreased with a tilt of more than 5 degrees in the 3-o'clock direction. The stability ratio in the 9-o'clock direction significantly decreased with a tilt of more than 15 degrees in the 9-o'clock direction and significantly increased with a tilt of more than 5 degrees in the 3-o'clock direction. The stability ratio in the 6-o'clock direction significantly increased with a tilt of more than 10 degrees in the 6-o'clock direction.
Conclusions: The posterior and inferior stability increased with an anterior tilt of more than 5 degrees and with a superior tilt of 10 degrees , respectively. The anterior and posterior stability decreased with an anterior tilt of 5 degrees and with a posterior tilt of 15 degrees , respectively.