Dislocated Shoulder Facts
If your shoulder is wrenched upward and backward, you may dislocate it out of its socket. This condition is both painful and incapacitating. The force required is often that of a fall or a collision with another person or object (both of which can occur during many sports).
Most shoulder dislocations happen at the lower front of the shoulder, because of the particular anatomy of the shoulder joint. The bones of the shoulder are the socket of the shoulder blade (scapula) and the ball at the upper end of the arm bone (humerus). The socket on the shoulder blade is fairly shallow, but a lip or rim of cartilage makes it deeper. The joint is supported on all sides by ligaments called the joint capsule, and the whole thing is covered by the rotator cuff. The rotator cuff is made up of four tendons attached to muscles that start on the scapula and end on the upper humerus. They reinforce the shoulder joint from above, in front, and in back, which makes the weakest point in the rotator cuff in the lower front.
Subluxation refers to a partial dislocation. A subluxation occurs when the two joint (articular) surfaces have lost their usual contact. A 50% subluxation means the normally opposing articular surfaces have lost half their usual contact and the joint is partially dislocated. A 100% subluxation means the articular surfaces have lost all of their contact. A dislocation is the same as a 100% subluxation.
The vast majority of shoulder dislocations (up to 98%) are anterior dislocations (in which the upper arm bone detaches from the shoulder socket and pushes forward). There are four types of anterior shoulder dislocations:
Posterior shoulder dislocations, in which the upper arm bone detaches and goes toward the back, are much less common (about 4% of all shoulder dislocations). The rarest type of shoulder dislocation is inferior glenohumeral dislocation (luxatio erecta humeri) and makes up just 1% of all shoulder dislocations.
Picture of Normal Shoulder Joint Picture of Shoulder Dislocation
Medically Reviewed by a Doctor on 11/18/2016
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