A shoulder dislocation is a form of injury in which the head of the humerus (upper arm bone) is forcibly pulled out of its socket in the scapula (shoulder blade). A shoulder dislocation can result from an accident or from forceful muscle contractions. A shoulder dislocation can also happen when an individual tries to pull themselves up by holding onto something with one hand while lifting their other arm.

The most common type of injury that causes a shoulder to become dislocated is a fall on an outstretched hand and arm, such as when trying to break a fall with one hand while catching oneself with the other.