AC osteoarthritis.

AC joint

Osteoarthritis of the AC jointure4) is a common finding in patients with rotator cuff disorders. However, its role in impingement remains unclear and could either be a risk factor for impingement or a result of rotator cuff injury and disturbed shoulder biomechanics. A large osteophyte arising from the inferior surface of the joint is thought to be a cause of tendon tear. MRI is more sensitive than radiography for detection of AC joint degenerative disease. MRI can differentiate joint enlargement due to capsular hypertrophy (intermediate signal intensity) form joint effusion (bright signal on T2-weighted images). Osteophytes appear in late stages of the disease.

Acromio-clavicular joint osteoarthritis. Coronal oblique fat-sat proton-density-weighted image shows degenerative changes of the acromio-clavicular joint (arrow) in a patient with rotator cuff tear.