Which movements should be avoided for posterior instability of the glenohumeral joint?

• A. Internal rotation with horizontal adduction and flexion
• B. External rotation with abduction
• C. Neutral rotation with extension
• D. Abduction with flexion

Answer: (A)

Posterior instability occurs when the posterior structures of the glenohumeral joint are lax, allowing the humeral head to translate backward within the socket. Movements that push the humeral head into this posterior direction—especially when the arm is flexed, adducted, and internally rotated—place the greatest stress on the posterior capsule and labrum. Internal rotation with horizontal adduction and flexion positions the arm in a flexed, adducted state with inward rotation, which drives posterior translation of the humeral head and reproduces symptoms. Because of that, this position should be avoided in rehab or activity modification for posterior instability. The other options are less provocative for posterior instability: external rotation with abduction tends to stress the anterior structures, while neutral rotation with extension or abduction with flexion does not place the shoulder into this posterior-dominant position as strongly.