Shoulder problems in pitchers are usually related to the rotator cuff muscles or the labrum. These are soft tissue structures that help stabilize the shoulder during the throwing motion. Luckily for Mariano Rivera, the shoulder pain that he had during last season was related to his acromioclavicular joint (or AC joint).
The AC joint is located on top of the shoulder where the distal end of the clavicle (or collarbone) meets the acromion. Like other joints, the ends of each bone are covered with cartilage, which allows the bones to smoothly glide over each other with movement. Ligaments surround the joint to help keep it stable. When one talks about shoulder separations in football or hockey players, it is often these ligaments that tear. More often however, overuse leads to a degeneration of the cartilage in the joint known as AC joint arthritis. Calcifications, or deposits of calcium, can also form.
When the arm is used overhead, the AC joint is under stress. Frequently weightlifters will develop arthritis in that joint, but even repetitive throwing can cause the condition. These injuries often occur in middle-aged people, and as scary as it is to admit, Mariano Rivera is approaching 40, making him middle-aged.
Patients with AC joint arthritis typically have pain on top of their shoulder right above the joint, and the pain is exacerbated when the arm is brought in front of the chest. In baseball players this motion would occur right after the ball is released during the throwing motion.
Treatment options for AC joint arthritis range from anti-inflammatory medication usage to injections to surgery. If oral medications fail to relieve the symptoms, a cortisone injection may alleviate the pain. Recalcitrant symptoms would be an indication for surgery, which involves cutting off a small piece of the end of the clavicle to provide more room between the clavicle and acromion. Years ago this was done through an open incision on top of the joint, but now it can be done arthroscopically. This involves using a small camera and a shaver through small poke-holes in the skin to remove the bone. Arthroscopy reduces the risks associated with open surgery and makes the postoperative rehabilitation easier. David Altchek, Chief of the Sports Medicine Service at The Hospital for Special Surgery and medical director for the NY Mets, performed Rivera's surgery arthroscopically.
After surgery, athletes start working on regaining their full range of motion, after which they begin strengthening exercises. Baseball players typically start a structured throwing program at an average of 3 months postoperatively. They begin by throwing on flat ground then work up to throwing off of the mound.
When professional baseball players have surgery on their rotator cuff or labrum, only about 80% of them return to their previous level of play. The AC joint does not play as critical a role during the throwing motion, which should theoretically make Rivera's recovery a bit easier, and he has an excellent chance of getting back to his previous position as one of the best closers in baseball.
Good luck on the surgery and recovery!