Shoulder OA

Shoulder osteoarthritis (OA) affects 2 joints with different presentations: the acromioclavicular joint (ACJ), causing pain at the top of the shoulder, and the glenohumeral joint (GHJ), causing deep pain and global stiffness.

ACJ OA is a common incidental finding on imaging and is often asymptomatic. Primary GHJ OA is less common than hip or knee OA but can cause substantial disability. Secondary GHJ OA follows trauma, instability, rotator cuff tear arthropathy, avascular necrosis (AVN) or inflammatory arthritis. Current NICE osteoarthritis guidance sets first-line management for both.

The ACJ is a small synovial joint between the lateral clavicle and the acromion, stabilised by the acromioclavicular and coracoclavicular ligaments. Its fibrocartilaginous disc degenerates early. ACJ OA becomes more common with age, particularly in weightlifters and manual workers. In a systematic review, 70% of asymptomatic shoulders on MRI showed ACJ OA changes.

The GHJ is a shallow ball-and-socket joint that relies on the labrum, capsule and rotator cuff for stability. Primary GHJ OA causes progressive cartilage loss, subchondral sclerosis, osteophytes and capsular thickening, often with posterior glenoid wear.

Causes of secondary GHJ OA:

• •Rotator cuff tear arthropathy: a chronic massive cuff tear allows the humeral head to migrate superiorly
• •Post-traumatic, after proximal humeral fracture or dislocation
• •Post-instability, after recurrent dislocation or stabilisation surgery
• •AVN: corticosteroid use, alcohol excess and sickle cell disease are recognised risk factors
• •Inflammatory arthritis: rheumatoid arthritis, spondyloarthropathy