Bone Lesions in Pigmented Villonodular Synovitis

Pigmented villonodular synovitis is a rather rare disease affecting the synovial membrane of various joints, bursae and tendon sheaths.It may appear in either a diffuse or a localised form.The aetiology of this condition is unknown, although various theories have been postulated, such as repeated minor trauma to the synovium (Greenfield & Wallace 1950, Wright 1951, Fisk 1952, Young & Hudacek 1954), a local disturbance in lipoid metabolism (Atmore et al. 1956, Kumon 1969, Hirohara & Morimoto 1971), and an inflammatory process (Jaffe 1964, Aegerter & Kirkpatrick 1968, Byers et al. 1968).Infection, however, is accepted as the cause of the disease by most writers, but the aetiological agent is still unknown.The pathological findings in the early stages of the disease consist of a non-specific inflammatory reaction of the synovial membrane which becomes oedematous and thickened.As the proliferative reaction progresses several cells are found infiltrating the synoviiim as plasma cells, histiocytes, fibroblastic cells and giant cells.Lipid-bearing xanthoid cells and macrophages are also seen.The stroma resembles undifferentiated mesenchymal tissue.Macroscopically the synovial membrane is oedematous and hypertrophic, with villus or nodular proliferation and with a brown colour due to pigmentation with haemosiderin.Pigmented villonolular synovitis is a monoarticular condition usually affecting the knee and the phalangeal joints, whereas the hip, elbow, ankle and other joints are rarely involved (Byers et al. 1968, Nilsonne & Moberger 1969).Bone lesions in pigmented villonodular synovitis are only occasionally seen in the joints usually affected by the disease.They are not uncommon, however, in the rarely involved joints (Jaffe 1960, Chung & Janes 1965).But even in these joints only a few cases Young, J. M. & Hudacek, A. G. (1954) Experimental production of pigmented villonodular synovitis in dogs.Amer.J .Path.SO, 799.