ACJ (Acromioclavicular Joint) Arthritis

The Acromioclavicular Joint (ACJ) is a small joint made up of the acromion bone, which is part of your shoulder blade, and the outer end of your clavicle (collar bone). It is easily palpated with your finger as it lies 1 – 2 cm from the top outer edge of your shoulder. Because of its location, problems with the joint can give rise to pain in both the shoulder and neck.

Arthritis is a chronic degenerative disease that results in the progressive softening and loss of the cartilage that covers a joint surface. It can also be accompanied by the formation of new, but abnormal, cartilage and bone at the margins of the joint. This ecess bone is termed an osteophyte. When osteoarthritis affects the acromioclavicular joint it results in the joint becoming painful and stiff and if osteophytes develop around the periphery of the joint, then the joint may also appear more prominent and it can be tender to touch.

Causes & Risk factors

The main cause of osteoarthritis is degeneration through general wear and tear / age. As the cartilage of the joint surface becomes worn out, the joint becomes stiffer and therefore more prone to pain during shoulder movements. This can occur without giving rise to significant symptoms however it can also become symptomatic after a seemingly minor injury to the joint.

An injury to the acromioclavicular joint is another cause of developing ACJ osteoarthritis. This may occur in an individual who performs a lot of heavy lifting or alternatively in one who undertakes repetitive lifting to, or above, shoulder height where repetitive minor injuries occur. Similarly it may also occur following a single, yet more significant, injury such as an ACJ dislocation or subluxation.


The diagnosis is essentially made on clinical grounds. Pain is often most noticeable when the arm is raised above shoulder height and when the arm is taken across the front of the body thus compressing the acromioclavicular joint.

X-rays can be used to demonstrate the loss of the joint space or the presence of small cysts, which are the key findings of osteoarthritis. It can also reveal the presence of osteophytes that can result in either a bony prominence over the shoulder or indeed one that protrudes beneath the joint and into underlying tendons of the rotator cuff. This can result in impingement like symptoms. If the underlying tendons are believed to be affected by the osteophytes an ultrasound or MRI scan can be used to further investigate the shoulder.

If there is any doubt over the diagnosis an injection of local anaesthetic into the ACJ can be undertaken. If this is done with ultrasound guidance, the presence of inflammation within the ACJ can also be visualised. If the pain subsides following an injection then this is usually a good indicator that the ACJ involved in the causation of the shoulder pain.


There are a number of different treatments available to address the pain from ACJ osteoarthritis:

  • Conservative treatment comprising of rest, activity modification and the use of anti-inflammatory medications.
  • Physiotherapy; this can be used to improve the range of movement to the shoulder and may help prevent the loss of further movement with the progression of the osteoarthritis. Its success is often dependant on the degree of pain experienced, as the pain will ultimately influence the amount of exercise that may be possible.
  • Injection treatments; the space between the acromion and the distal clavicle can be injected with local anaesthetic and Cortisol. The anti-inflammatory component of the injection can reduce swelling and pain and an injection can be used in conjunction with physiotherapy to aid recovery. It however usually only provides temporary relief.
  • Arthroscopic ACJ excision; If the pain is resistant to non-operative treatments then surgery is often necessary. The aim of the surgery is to arthroscopically remove any degenerative tissue that has herniated out inferiorly from the joint and then excise a small amount of the arthritic distal clavicle. If there is evidence that the underlying rotator cuff tendons have been aggravated by the diseased ACJ,, then a subacromial decompression can also be performed. This ‘key-hole’ procedure is performed through 3 small incisions.
  • Open distal clavicle excision; This allows direct visualisation of the distal clavicle and may be used if a large open operation is also being undertaken for the management of other significant shoulder conditions, which are not amenable to arthroscopic techniques.