Orthopedics focuses on the musculoskeletal system. Learn about the diagnosis, treatment, and rehabilitation of bone, joint, ligament, and muscle conditions.
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Overview and Definition
The shoulder is the most mobile joint in the human body, a marvel of engineering that allows us to reach, throw, lift, and embrace. It functions as a ball-and-socket joint, similar to a golf ball sitting on a tee. This design grants an incredible range of motion, but it comes with a trade-off: stability. Because the socket is shallow and the ball is large, the shoulder relies heavily on soft tissues—muscles, tendons, and ligaments—to keep everything in place. When force overwhelms these soft tissues, the ball has the potential to pop out of the socket. This is a shoulder dislocation.
A dislocation is a significant event. It is not just a “pop” that goes back in; it is a traumatic injury where the head of the upper arm bone (humerus) is forced completely out of the shoulder blade socket (glenoid). This event stretches and often tears the ligaments and the capsule that hold the joint together. For many people, a dislocation is a one-time, painful accident. For others, it can become a chronic issue, leading to a loose, unstable shoulder that dislocates repeatedly with minimal effort. This section will guide you through the anatomy of the shoulder, what actually happens during a dislocation, and the difference between a partial slip and a full dislocation.
To understand a dislocation, you must first visualize the joint. The shoulder is made up of three main bones: the upper arm bone (humerus), the shoulder blade (scapula), and the collarbone (clavicle). The head of the humerus fits into a shallow dish on the scapula called the glenoid. To deepen this shallow dish and provide a better seal, there is a rim of tough, rubbery cartilage called the labrum. The labrum acts like a gasket or a bumper, helping to keep the ball centered.
Surrounding the joint is a watertight sac called the joint capsule, which is strengthened by ligaments. On top of this are the rotator cuff muscles, which actively pull the ball into the socket. When a dislocation occurs, the ball is forced out of this containment system. In the process, it often tears the labrum off the bone (a Bankart lesion) or stretches the capsule beyond its elastic limit. This damage to the “containment wall” is the primary reason why shoulders can become unstable after the first injury.
A shoulder dislocation occurs when the humerus head is completely separated from the glenoid socket. It is distinct from a separation, which involves the ligaments connecting the collarbone to the shoulder blade (AC joint). In a dislocation, the ball usually pops out the front of the joint (anterior dislocation), which is 90% of cases. This condition typically happens when the arm is raised and forced backward, like when throwing a ball or blocking a shot.
Less commonly, the shoulder can dislocate out the back (posterior dislocation), often due to seizures or electric shocks where powerful muscle contractions force the joint apart. Even rarer is an inferior dislocation (luxatio erecta), where the arm is stuck straight up over the head. Regardless of the direction, a dislocation is a medical emergency that requires immediate attention to put the joint back in place and prevent nerve or blood vessel damage.
Patients often confuse these two terms. A dislocation is a complete separation where the bones are no longer touching. The joint is “out,” and you cannot move it normally until it is put back (reduced). A subluxation is a partial dislocation. The ball slips partially out of the socket but then slides back in on its own.
While a subluxation might seem less severe, it is a sign of significant instability. It means the ligaments are loose or damaged enough to allow the ball to ride up onto the rim of the socket. Repeated subluxations can damage the cartilage and the labrum just as much as a full dislocation. Both conditions signal that the shoulder’s stability system is compromised and needs evaluation.
One of the primary challenges with shoulder dislocations is the high rate of recurrence, especially in young people. When the shoulder dislocates, it stretches the ligaments like an overblown balloon. Unlike a balloon, these ligaments often do not snap back to their original tightness. They remain loose and baggy.
Additionally, if the labrum is torn, the “bumper” that keeps the ball in place is gone. This creates a situation where it takes decreasing force to pop the shoulder out again. A young athlete who dislocates their shoulder has a very high chance—sometimes over 80–90%—of dislocating it again if they return to sports without surgical stabilization. This cycle of dislocation, pain, and apprehension is known as chronic shoulder instability.
A dislocated shoulder is not something to “wait out.” The displaced bone can press on the nerves (axillary nerve) or blood vessels passing through the armpit. These injuries can cause numbness, weakness, or circulation problems in the arm and hand. Furthermore, the longer the shoulder sits out of joint, the more the muscles go into spasm, making it incredibly difficult and painful to put back in.
Getting professional help quickly allows for a safer reduction (putting it back in). Doctors can use medication to relax the muscles and imaging to ensure there are no broken bones before manipulating the joint. Trying to force it back in yourself or having a friend do it can cause fractures or nerve damage.
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You will feel intense pain and likely an inability to move the arm. The shoulder will look visibly deformed—squared off rather than round—and you may feel a bulge in the front of the shoulder where the ball has moved.
The soft tissues can heal, but they often heal loosely. The bone will not go back into place on its own; it must be manipulated. Once back in, the ligaments need time and rehab to tighten up, but they may never be as tight as before without surgery.
No. You risk trapping a nerve, breaking a bone, or tearing more soft tissue. Always seek medical attention. If you are in a remote wilderness situation, specific techniques exist, but they should only be used as a last resort.
It keeps happening because the primary stabilizers—the labrum and ligaments—were torn or stretched during the first injury. Without this structural support, the shoulder relies solely on muscles, which can fatigue and fail to hold the joint.
Often, yes. As the tissues become looser, it takes less force to dislocate the shoulder, and there is less tissue damage with subsequent events. However, the damage to the joint surface (arthritis risk) continues to accumulate with every episode.
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