What is acromioclavicular osteoarthritis?

What is Acromioclavicular Osteoarthritis?

Acromioclavicular (AC) osteoarthritis is degenerative joint disease affecting the articulation between the acromion process of the scapula and the distal clavicle, representing one of the most common causes of shoulder pain, particularly in middle-aged adults. 1, 2

Pathophysiology and Types

• AC osteoarthritis results from degeneration of the fibrocartilaginous disk that cushions the joint articulation, most commonly occurring in middle-aged individuals 3
• The condition arises from several pathologic processes including primary (degenerative), posttraumatic, inflammatory, and septic arthritis 1
• The AC joint is frequently affected by osteoarthritis due to its high mobility and load-bearing function during shoulder movements 2

Clinical Presentation

• Patients typically present with nonspecific complaints of pain located in the neck, shoulder, and/or arm, which can complicate diagnosis 1
• Pain characteristically occurs with overhead activities and cross-body adduction movements 3
• The pain is typically localized to the anterior or superior shoulder region 3
• Symptoms may be intermittent and vary with activity level 1

Diagnostic Approach

• Diagnosis requires a thorough physical examination, plain-film radiography, and diagnostic local anesthetic injection to confirm the AC joint as the pain source 2
• Physical examination findings alone lack specificity, as similar findings can occur in asymptomatic individuals 3
• Plain radiographs can reveal degenerative changes, but radiographic findings alone cannot establish the diagnosis since similar changes appear in asymptomatic patients 3
• Diagnostic local anesthetic injection into the AC joint is crucial to differentiate symptomatic AC osteoarthritis from other shoulder pathology 2, 3

Epidemiology and Risk Factors

• AC osteoarthritis is the most common disorder of the acromioclavicular joint 1
• The condition predominantly affects middle-aged adults due to cumulative degenerative changes 3
• Following total shoulder arthroplasty, approximately 16% of patients develop symptomatic AC joint osteoarthritis, with the majority developing symptoms within the first two years 4

Important Clinical Distinctions

• Symptomatic AC osteoarthritis must be differentiated from AC joint instability and subtle instability, which may present with similar symptoms but require different management 3
• The AC joint can be overlooked as a pain source because the majority of shoulder pain originates from the subacromial region and glenohumeral joint 2
• Ultrasound and imaging can evaluate the AC joint, though diagnosis relies primarily on clinical correlation with injection response 5