At 90 degrees of gleno-humeral abduction, the primary restraint to inferior translation of the humerus is which ligament?

• A. Superior glenohumeral ligament
• B. Middle glenohumeral ligament
• C. Inferior glenohumeral ligament
• D. Coracohumeral ligament

Answer: (C)

At 90 degrees of glenohumeral abduction, the inferior glenohumeral ligament is the primary restraint to inferior translation of the humerus. This ligament is particularly important for preventing excessive inferior movement of the humeral head when the shoulder is positioned in abduction and external rotation, conditions that increase the risk of dislocation.

The superior and middle glenohumeral ligaments primarily provide stability to the shoulder joint at lower levels of abduction. They are more effective at preventing anterior and inferior translation at lower degrees of shoulder elevation. The coracohumeral ligament offers some stability, but it primarily restricts excessive movement in different planes rather than specifically controlling inferior translation at higher angles of abduction.

In the position of 90 degrees of abduction, the inferior glenohumeral ligament becomes taut and functions to support the joint, effectively limiting inferior translation and contributing to the overall stability of the glenohumeral joint under these conditions.