ACROMIOCLAVICULAR (AC) JOINT PROBLEMS

The AC joint is a particularly troublesome little area that causes a myriad of shoulder pain syndromes.  Pain from the AC joint can run up into the neck or down into the hand, but is usually localized to the joint itself.  There is often grinding and catching in the joint with no known injury.  The structural reason is that many of the stresses from the arm are transmitted to the body through the AC joint, since the AC joint provides the articulation between the platform of the shoulder (the shoulder blade) and the clavicle (collar bone).  Just by normal activities of daily living, the cartilage cap on the end of the collar bone can wear down and cause the grinding and snapping symptoms.  Fortunately, AC joint problems are usually easy to diagnose, since it is never normal for the AC joint to be tender.

The vast majority of AC joint problems fall into two categories:  AC joint arthritis and AC joint separations. AC joint arthritis is a wear and tear problem and comes from the front and back motion in the joint as we reach with our shoulders in various directions.  It is easily diagnosed by tenderness and sometimes spurring of the joint.  Injection of local anesthetic and corticosteroid often cures the problem for awhile.  AC joint arthritis rarely leads to surgery and is not associated with glenohumeral arthritis of the ball and socket.  However, if the spurs become large enough, they can encroach on the rotator cuff tendons that glide beneath the joint and play a part in tearing of the cuff.

The second problem is AC joint separation (commonly known as a separated shoulder) and often occurs from a fall directly onto the side of the shoulder.  Most AC separations are fairly painful for 3-6 weeks, but do not require surgery.  As the injury forces increase (as in a fall from a mountain bike) the separations tend to be more severe and do require repair (some Type III, all Type 4,5,6)