Shoulder dislocation occurs when the ball-shaped head of the upper arm bone, called the humerus, is dislodged from the shoulder socket, called the glenoid. Dislocation may be partial, when the humerus isn’t completely removed from the socket, or total, when the humerus is forced completely out of the glenoid.
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Shoulder dislocation almost always results from a sudden traumatic injury, such as a hard fall onto an outstretched arm. Certain sports can also increase your risk of a shoulder dislocation. Forcefully throwing a baseball or football can cause a dislocation, as can a hard tackle, especially if the player is tackled while an arm is outstretched.
Often, the soft tissues that surround the shoulder and help keep your arm in place are torn or stretched as the result of a dislocation. These soft tissues include ligaments, which connect the bones of the joint; tendons, which connect muscle to bone; and the labrum, which is a ring of cartilage that surrounds the shoulder socket and connects to the ligaments.
All of these structures help the humerus stay in place. If the soft tissues don’t heal fully after a dislocation, there’s an increased risk of recurring dislocations. This is more common among young athletes than in less active older people.
Symptoms of shoulder dislocation are evident right away. You may feel a popping sensation as the joint dislocates, as well as a sharp pain in the shoulder or pain radiating down the arm. The shoulder may look sunken or pushed forward, and there may be bruising and swelling.
Regardless of whether the dislocation is partial or total, your shoulder feels weak and possibly numb. You may not be able to move your arm at all. The muscles surrounding the shoulder may twitch or spasm as a result of the force of the injury, causing additional pain. If the injury has damaged nearby nerves, you may feel tingling or numbness in the shoulder, arm, or fingers.
Sports medicine doctors and specialists at NYU Langone Orthopedic Center diagnose shoulder dislocations based on your symptoms, medical history, and the results of diagnostic imaging tests. They can distinguish a shoulder dislocation from a shoulder fracture, which is a break in a bone; tears to the labrum or rotator cuff, which damage soft tissues; and a shoulder separation, which affects the ligaments connecting the acromioclavicular joint, where the collarbone meets the shoulder blade.
A detailed description of your symptoms and medical history helps doctors determine the nature of your shoulder injury. Doctors may ask when the injury occurred, how it happened, where you feel pain, if your range of motion is limited, and if you feel tingling or numbness. In addition, doctors ask about previous injuries, which may determine how to move forward with treatment.
A doctor thoroughly examines your shoulder for signs of injury and evaluates the strength of and range of motion in your arm. He or she evaluates the shoulder’s appearance; for example, if the area in front of the shoulder looks sunken in, it’s likely that the arm bone has popped completely out of the socket. Your doctor may put gentle pressure on different parts of the shoulder to test for tenderness.
Doctors often recommend X-rays to obtain more information about a dislocated shoulder. X-rays use high-energy beams of light to create pictures of the bones in the shoulder joint. Doctors use X-rays to see if the humerus has moved out of place and, if so, in what direction and how far.
X-rays can also reveal a fracture in one of the three bones that make up the shoulder: the humerus; the scapula, or shoulder blade; and the clavicle, or collarbone.
MRI scans use a magnetic field and radio waves to create computerized, three-dimensional images of soft tissues inside the body. These scans can reveal injured ligaments or tendons surrounding the shoulder joint, as well as the location of a tear in the labrum, the ring of soft tissue surrounding the shoulder socket.
MRI scans can reveal areas of bone that have sustained tiny microfractures, as well as areas of bone that are actively healing.
CT scans use X-rays and a computer program to create two- and three-dimensional images of the shoulder. CT scans display bones in sharper detail than regular X-rays and can reveal subtle damage to components of the shoulder joint. For example, if a shoulder has dislocated several times, areas of the socket may have chipped, contributing to long-term instability in the shoulder.
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