Acromioclavicular Arthritis, Osteoarthritis is the most common cause of shoulder pain originating from the acromioclavicular (AC) joint. ACJ osteoarthritis is a frequent finding in middle-aged people.
Most of the patients are asymptomatic, and they may present as an incidental finding in shoulder X-Ray or Magnetic resonance imaging (MRI). Pain and dysfunction of ACJ origin may lead to an inability to perform manual labor tasks and sports and difficulty doing overhead and cross-body activities. Functional limitations of ACJ pain include difficulty with resistance-training activities that place the glenohumeral joint in an extended position, common in weightlifters so ACJ arthritis is also known as Weightlifter’s Shoulder.
AC joint arthritis is caused due to early degeneration of the cartilage and intraarticular disc. Arthritis is often associated with distal clavicular osteolysis. Damage to the ACJ can be synchronous with damage to the supraspinatus tendon and osteophytes from the arthritic joint may contribute to subacromial impingement exacerbating and producing further shoulder pain.
Clinically Relevant Anatomy
The ACJ is a synovial joint that provides the scapula with an additional range of rotation on the thorax, which allows the scapula to adjust outside of its initial plane (posterior tipping and internal rotation) to follow the changing shape of the thorax as arm movement occurs.
12-month prevalence of shoulder pain has been estimated to be 30%, which is second only to low back pain.
Acromioclavicular joint (ACJ) disease is reported to be present in 31% of all patients with shoulder pain.
The incidence of ACJ pain is reported to be between 0.5 to 2.9/1000/year in primary care.
However, the true prevalence is still not clear because most of the time arthritic changes go on silently without producing any symptoms which makes diagnosis more difficult.
It is common in middle-aged people.
Type of AC joint arthritis-Based on the etiology
Primary osteoarthritis: It is articular degeneration without any apparent underlying cause. It more commonly affects the AC joint than a glenohumeral joint. It develops as a consequence of constant stress on the joints, often in people who perform repeated overhead lifting activities.
Secondary osteoarthritis: It is due to other associated causes like post-trauma or other underlying diseases such as rheumatoid arthritis. Post-traumatic AC joint arthritis is even more prevalent due to the high incidence of injury to the joint. Arthritic symptoms have been demonstrated in Grade I and II sprains of the AC joint in 8% and 42% of patients, respectively.
Accurate diagnosis and localization of pathology to the AC joint is vital in determining the correct treatment protocol in order to avoid persistent shoulder pain. The proper diagnosis of ACJ arthritis requires a thorough history taking, physical exam, plain-film radiograph, and a diagnostic local anesthetic injection.
History and on observation
History of trauma: direct impact on the joint or a fall on an outstretched arm.
Occupational history: an occupation that requires repeated overhead lifting activities, involvement in sports like weightlifting, rugby, etc.
A patient may complain of pain at night during sleeping on the affected shoulder.
Patients may complain of popping, clicking, grinding, or catching sensation with the movement of their shoulder.
Possibly swelling in the shoulder as a presence of distal clavicle osteolysis.