What is Shoulder Instability?
The shoulder is comprised of three bones; the humerus (upper arm bone), scapula (shoulder blade), and the clavicle (collarbone). The top of the humerus bone (humeral head) joins the shoulder socket (the glenoid, which is part of the scapula) to form the shoulder joint (glenohumeral joint). The glenoid is a very shallow socket. Attached circumferentially to the edge of the socket is the labrum, which is a bumper of tissue somewhat like the orange rubber gasket on a mason jar. The ligaments that hold the ball in the socket attach to the labrum, and both the labrum and the ligaments provide stability to the shoulder. Because the glenoid is almost flat and not a deep bony socket like the hip socket, the glenohumeral joint allows for more range of motion than any other joint in the body. However, this freedom of motion also makes the shoulder joint the most susceptible to dislocations and instability.
Shoulder instability is a condition in which the humeral head gets pushed out of the glenoid. The humeral head usually gets pushed completely off the edge of the glenoid (a glenohumeral joint dislocation). However, the humeral head can get pushed only partially out of the glenoid (a glenohumeral joint subluxation).
Dr. Cunningham is a shoulder specialist at Vail Summit Orthopaedics and Neurosurgery. He is an expert at diagnosing and treating shoulder instability for patients in Vail, Summit County, Aspen, and Denver, CO.