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 s
lip in and out of the patellofemoral articulation during flexion and e
xtension, The snapping caused by the solitary mass was noticed as the
joint flexed from 15 degrees to 30 degrees in 9 knees and from 50 degr
ees to 60 degrees in 3. Histopathological examination of the masses re
vealed typical findings of a rheumatoid nodule in 4 knee joints and my
xomatous degeneration and collagen necrosis in 7.