Posterior Shoulder Instability

Posterior shoulder instability is when the ball of your shoulder slips backward out of its socket — the opposite direction from the much more common forward (anterior) instability. It only accounts for about 5-10% of shoulder instability cases, but it's frequently missed because the symptoms are subtle: a vague clunk or weakness instead of an obvious dislocation. It shows up most in weight lifters (the bench-press position loads the shoulder backward), football linemen, and swimmers. There's also a separate, less common version where someone can intentionally make their own shoulder slip out the back — that's a different problem with its own treatment path.

• Vague deep shoulder pain — an ache in the back of the shoulder, especially during bench press, push-ups, or overhead pushing motions.
• Dead-arm episodes — a sudden feeling that the arm loses all power, usually when your hand is forward and rotated inward.
• Clunking or shifting — you feel the ball slip and catch when you move through certain positions, particularly with the arm across your body.
• Weakness with forward-directed force — pushing a door open, blocking in football, or finishing a swim stroke feels unreliable.
• Apprehension with specific positions — you instinctively avoid the arm-forward, internally-rotated position because it feels like the shoulder is about to slip.

Pain — and sometimes a sudden "dead arm" feeling — when your arm is held forward, across your body, and rotated inward. That position loads the shoulder straight backward and is when the slipping happens. Your provider does the load-and-shift and jerk tests to confirm the joint is loose toward the back. An MRI with contrast injected into the joint (MRI arthrography) shows whether the back rim of the cushion (a reverse Bankart lesion) is torn and whether the socket is angled in a way that predisposes to slipping.

When a long course of dedicated rehab hasn't stabilized the shoulder and imaging confirms a real tear at the back rim of the socket, surgical repair is the next step. The torn cushion is reattached to the bone with small anchors.

External patient-education references and related OSI pages for additional background:

• Britannica — Dislocation
• Britannica — Shoulder (anatomy)
• AAOS OrthoInfo — patient education library
• OSI glossary — orthopedic terminology in plain language