Shoulder Dislocation

The shoulder is the most commonly dislocated joint in the body, and it pays for its remarkable range of motion with a correspondingly loose fit. The head of the humerus (the ball) sits against a shallow, almost flat surface on the scapula called the glenoid (the socket), held in place largely by soft-tissue restraints — the labrum that deepens the socket, the joint capsule, and the surrounding rotator cuff tendons. When a force drives the arm backward and outward, as in a tackle or a fall with an outstretched arm, those soft-tissue restraints give way and the ball slides forward out of the socket. Nearly all dislocations (around 95%) go in this anterior direction; the less common posterior dislocation is classically caused by a seizure, an electric shock, or a heavy eccentric load.

The first dislocation almost always does lasting damage to the structures that hold the joint together. The labrum and anterior capsule often tear off the front rim of the socket — a Bankart lesion — and the back of the humeral head can dent where it impacted the rim of the glenoid on the way out. Once the soft-tissue restraints are stretched or torn, the shoulder is at real risk of dislocating again, and the probability is highest in younger patients with the greatest number of future years at risk. This is why a first shoulder dislocation is not just an event to be reduced and forgotten — it is the beginning of a stability problem that has to be managed.

• Sudden, severe shoulder pain after a fall, tackle, or forced arm motion
• The shoulder looks visibly deformed — squared-off instead of its normal rounded contour
• Complete inability to move the arm — you hold it protectively against your body
• A visible or palpable hollow just below the bony point of the shoulder where the ball should be
• Numbness or tingling over the outer shoulder or down the arm (a sign the axillary nerve was stretched)
• Rapid swelling and bruising around the shoulder joint

Sudden severe shoulder pain with the arm held protectively to the side. With an anterior (forward) dislocation, the shoulder looks squared-off — you can sometimes see and feel an empty space just under the bony point of the shoulder where the ball should be. Before and after popping the joint back, your provider checks for nerve injury — a nerve that runs around the back of the shoulder (the axillary nerve) is the one most often affected, showing up as a patch of numbness over the outer shoulder. X-rays after the reduction confirm the joint is back in place and look for any fractures that came along with the dislocation.

Surgery is the move when the shoulder keeps dislocating, when it's a first dislocation in a young contact-sport athlete (where the chance of it happening again approaches 90%), when an associated fracture needs fixing, or when too much bone has been lost off the rim of the socket for soft-tissue repair to hold.

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