MR imaging of arthritides affecting the shoulder.

MR imaging has had a limited role in the evaluation of arthritis involving the shoulder, despite studies that have shown this technique to be more sensitive than radiography in the evaluation of osseous erosions and cartilage loss. Factors responsible for limiting the use of MR imaging are its relatively high cost, as well as its insensitivity to diminished osseous mineralization and subtle areas of calcification or hyperostosis. MR imaging findings of some arthropathies, however--such as synovial osteochondromatosis, PVNS, and amyloid arthropath--are highly characteristic, and help in determining both diagnosis and treatment. Physicians also should be aware that MR imaging is highly effective at diagnosing numerous "secondary" conditions common in patients with shoulder arthropathies, including rotator cuff rupture, synovial cyst formation, and osteonecrosis.