The Acromioclavicular (AC) Joint is the small joint on top of the shoulder where the clavicle attaches. If the AC joint is hit head-on, such as when falling off a bike or tackling somebody without shoulder pads, the clavicle may detach, raise up and become noticeably ‘out of joint’. A dislocation occurs when no part of the clavicle remains touching the acromion bone that it normally sets into. A subluxation is a partial dislocation, meaning that the clavicle goes partially out of joint, with part of the clavicle still touching the acromion.
X-rays are necessary to confirm the diagnosis and make sure that a clavicle fracture isn’t present. Unless the AC joint injury occurs in a young manual laborer or an overhead athlete, it’s often best to wait for at least 3 months before considering any surgical reconstruction of the AC joint ligaments that hold the AC joint in place, even in a professional (non-overhead) athlete. The pain will usually subside faster and people usually return to sports quicker without surgery, even to collision sports such as football or rugby. The arm is placed in a sling for a couple of weeks to let the inflammation subside, and then range of motion exercises are begun, either at home or under the direction of a therapist. At 6 weeks, strengthening of the rotator cuff and muscles about the shoulder blade, which may also be affected by the injury, can begin.
The vast majority of people with AC joint injuries can be treated without surgery. The exceptions are when the clavicle is extremely high riding, if the clavicle has been forced backward through its restraining fascia (a sheet of stabilizing tissue), or forced downward under a bone called the coracoid (which is incredibly rare). Although these circumstances are uncommon, they do occur, and are a good reason to have any shoulder injury evaluated by a shoulder or upper extremity specialist.
If non-operative management fails to provide significant pain relief after 3 months, it’s usually because the AC joint ligaments didn’t heal on their own and the end of the clavicle remains unstable. This may lead to persistent pain with shoulder motion. Often, the end of the clavicle is so unstable that it can be moved around with a couple of fingers. In these cases, surgical stabilization may be considered.
There are many surgical stabilizations described to treat AC joint instability. All work fairly well, although some work better than others. However, none of them recreate a totally normal AC joint. I prefer to use a cadaveric hamstring tendon (semi-tendinosis allograft) to recreate the torn ligaments. This is an outpatient procedure. The clavicle is reduced back to its natural place and held there with a ligament reconstruction that includes the cadaveric hamstring tendon to add more strength. However, there is almost always some degree of stretch following surgery. While the clavicle usually raises up a little, it is usually stable enough so that it no longer hurts and full activities can be performed. To prevent the surgical reconstruction from stretching out too much, it is necessary to protect the shoulder until enough scar forms to provide strength. To protect the reconstruction, a sling is worn for 6 weeks with only limited motion allowed until then. Fortunately, despite this immobilization, the shoulder doesn’t usually get very stiff as the surgery is entirely outside of the shoulder joint. Overall, most people do very well following this surgery, and can return to their usual work and sporting activities by 4-6 months.