Reviewed by Dr. Jon Warner
The shoulder is made up of three bones: the clavicle, or collarbone; the scapula, or shoulder blade; and the humerus, or upper arm bone. The edge of the scapula is known as the glenoid, and forms the shoulder socket that the head of the humerus fits into. A dislocation of the joint, when the humerus is forced out of the glenoid, may occur after a severe blow to the shoulder or a fall on an outstretched hand. Reduction is the process that fits the humerus back into the socket. Because the most common dislocations are anterior dislocations, where the humerus pops out of the socket in a forward direction, reduction for those dislocations is detailed in this report.
Before the procedure, the surgeon will take a number of X-Rays to determine if there are any injuries associated with the dislocation: a Hill-Sachs defect, Bankart lesion, or other bone injury. He will also administer a physical examination to see if a torn labrum, blood vessel or nerve damage, or other condition have resulted from the dislocation. The doctor will also ask a series of questions to determine when the dislocation occurred, whether the patient has suffered from previous dislocations, and whether any allergies to medication exist.
For most dislocations, non-surgical or "closed" reduction is all that is necessary to fit the humerus back into the glenoid. Although a few closed reduction procedures exist, all have the same purpose: to relax the muscles of the shoulder enough to allow the head of the humerus to slide back into its rightful place, the glenoid. For example, the patient may be asked to lie on his or her back while the doctor applies a pulling force to the affected arm. The arm is then externally rotated—the same motion one would be forced into while losing an arm wrestling match. The patient may also lie face down while letting the affected arm dangle, allowing gravity to pull the arm down and in. A local or general anesthetic and/or nerve block is nearly always applied in closed reduction.
A patient may also suffer from a different type of dislocation: posterior (backward), inferior (downward) and superior (upward). Although these types of dislocations are extremely rare, similar reduction techniques apply. A traction, or pulling, force is applied to the arm to allow the head of the humerus to slide inside the glenoid.
Some cases exist where open reduction is necessary. This involves surgically cutting through into the shoulder with a scalpel and making incisions in the capsule, the group of ligaments that surrounds the joint. Next, the surgeon applies traction to the arm and rotates it to slide the arm back into the socket. Open reduction is often done in elderly patients or in patients whose dislocations have remained unreduced for more than a few hours, and is always applied under at least local anesthetic.