(Acromioclavicular joint degeneration)

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related talks: broken collar bone (clavicle fracture); broken shoulder (proximal humerus fracture); separated shoulder (AC joint); shoulder dislocationshoulder instabilitybroken arm (humeral shaft fracture); rotator cuff tear

What is AC Arthritis?

AC arthritis is the degeneration of the AC joint.  

The AC joint is the connection between the clavicle (aka the collar bone) and the acromion (the bony prominence of your shoulder). This joint is unusual because there is very little motion (compared to the shoulder for example).  However it still experiences a lot of stress, and the cartilage can breakdown over time.  Cartilage breakdown causes arthritis.  

AC arthritis is most common in long-time weight lifters, but can occur in many heavy-laborers or people who experienced a previous injury to their AC joint (like a shoulder separation, see talk). 

How is a AC Arthritis  diagnosed?

A person with AC arthritis will report pain in the shoulder, that is comes on gradually after many weeks.  There is no recent traumatic episode.  The pain is dull and achy.  And its worsened by bring the arm across the body. That is the provocative test (aka test which elicits pain) used to diagnose this injury, also called a "Bear Hug Test".

Diagnosis of AC joint arthritis is confirmed with an xray (which will show classic signs of arthritis).

How is AC arthritis treated?

Treatment should be approached in a stepwise fashion, from least invasive to more invasive.

Initially, anti-inflammatory medication can successfully treat the pain.  If it returns over time, or if it persists despite daily anti-inflammatory medication, then a steroid injection into the joint can be very effective.  

Surgery is the last resort treatment if all else fails.  

The procedure removes part of the collar bone (takes out the part that forms the joint) to prevent the arthritic joint friction which is the source of pain.  The surgery is typically effective in providing pain relief, however, it can cause the collar bone to become unstable (some of the stabilizing ligaments are removed with the surgery).  An unstable collar bone may displace upward, or backward, and bump into your shoulder blade, causing a new type of pain.  These are risks that should be discussed with your doctor before electing for any procedure.  



1) Shaffer BS. Painful conditions of the acromioclavicular joint. JAAOS 1999; 7: 176-88. full article. review.

2) Needell SD et al.  MR imaging of the rotator cuff: peritendinous and bone abnromalities in an asymptomatic population. AJR 1996; 166: 863-867. full article. nearly 50% of elderly people have signs of ac arthritis, but are asymptomatic. cannot rely on imaging alone. symptomatic ac arthritis is much less common than knee/hip etc.

3) Bergfeld JA et al. Evaluation of the acromioclavicular joint following I and II degree sprains. Am J Sports Med 1978; 6: 153-59. full article. near 40% rate of symptomatic arthritis long term.  overall varies 8-40% but much more common than primary OA for the ac joint. 

4) Cahill BR. Osteolysis of the distal part of the clavicle in male athletes. JBJS 1982; 64: 1053-58. full articledistal clavicle osteolysis is microtrauma causing bone destruction over time seen in weight lifters


5) Mumford EB. Acromioclavicular dislocation: a new operative treatment. JBJS 1941; 23: 799-802. full article. classic paper: original description of distal clavicle resection.

6) Freedman BA et al. Arthroscopic versus open distal clavicle excision: comparative results at six months and one year from a randomized, prospective clinical trial. J Shoulder Elbow Surg 2007; 16: 413-18. full article. both provide good pain relief, however scope also eval of patient for additional pathology