Painful snapping in rheumatoid knees.

Painful snapping caused by a solitary intra-articular nodular mass was found in 11 knee joints of 8 patients with rheumatoid arthritis. The masses were characteristically situated in the anterolateral aspect of the lateral femoral condyle of each joint, and appeared to jump and slip in and out of the patellofemoral articulation during flexion and extension. The snapping caused by the solitary mass was noticed as the joint flexed from 15° to 30° in 9 knees and from 50° to 60° in 3. Histopathological examination of the masses revealed typical findings of a rheumatoid nodule in 4 knee joints and myxomatous degeneration and collagen necrosis in 7.