Acromioclavicular (AC) Joint Instability, Subluxation & Dislocation

The Acromio-Clavicular (AC) Joint is the small joint on top of the shoulder where the clavicle inserts.  If the AC joint is hit head-on, such as when falling off a bike or tackling somebody without shoulder pads, the clavicle can dislocate from the AC joint, spring upwards and become prominent / noticeably ‘out of joint’.

Some definitions: An AC Joint Dislocation occurs when no part of the clavicle remains touching the acromion bone that it normally sets into. An AC joint Dislocation looks like a large bump on top of the shoulder. An AC Joint Subluxation is a partial dislocation, meaning that the clavicle goes partially out of joint, with part of the clavicle still touching the acromion. An AC Joint Subluxation looks like a small bump on top of the shoulder.

Shoulder X-rays are necessary to confirm the diagnosis and make sure that a clavicle fracture isn’t present. Unless an 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, even in a professional (non-overhead) athlete. The pain will usually subside faster with a quicker return to sports without surgery, even for football or rugby players. The arm is placed in a sling for 2 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 shoulder blade muscles, which are often affected by the injury, can begin.

The majority of people with AC Joint injuries can be treated without surgery.  The exceptions are: 1) When the dislocated clavicle is extremely high, 2) If the clavicle has been forced too far backwards, or 3) If the clavicle has been forced too far downwards.  Although these circumstances are uncommon, they do occur, and are a good reason to have any AC Joint injury evaluated by a Shoulder or Upper Extremity Surgeon.

If non-operative management fails to provide significant pain relief after 3 months, it’s usually because the AC Joint ligaments didn’t scar in enough on their own and the end of the clavicle remains unstable. This AC Joint Instability can lead to persistent pain with shoulder motion. Often, the end of the clavicle is so unstable that it can be moved around with two fingers. In these cases, surgical stabilization should be considered.

There are many surgeries 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. Most surgeries reconstruct one of the two sets of AC Joint Ligaments. I prefer to reconstruct both sets of AC Joint Ligaments (one horizontal, one vertical), for added stability. I prefer to use a cadaveric hamstring tendon (semi-tendinosis allograft) to recreate these torn AC Joint ligaments. This is an outpatient procedure. The clavicle is reduced back into its natural position in the AC Joint and held there with two separate AC Joint ligament reconstructions using a cadaveric hamstring tendon.

All AC Joint surgeries almost always have some degree of ligament stretch afterwards. While the clavicle usually rises up a little, it is usually stable enough so that the AC Joint no longer hurts. In my experience, repairing both sets of AC Joint ligaments decreases this post-operative stretch. In order to further minimize this post-operative ligament stretch, it is necessary to protect the shoulder until enough scar forms to strengthen the AC Joint Ligament Reconstructions. Therefore, after surgery, a sling is worn for 6 weeks with only limited motion allowed. Despite this immobilization, the shoulder doesn’t usually get very stiff as the AC Joint Ligament Reconstruction is entirely outside of the shoulder joint. Overall, most people do very well following AC Joint Ligament Reconstruction, and can return to their usual work and sporting activities by 4-6 months.