[Results of arthroscope studies of knee joint effusions of unknown origin]

174 knee joints with non-traumatic effusion have been examined by arthroscopy. In 71 cases synovial biopsy was performed. 43% of the knees had cartilaginous damage of the patella or tibiofemoral joint, 19% had an old meniscal and/or ligamentous tear and 33% a "non-specific" synovitis. The remaining 5% comprise 5 patients with pigmented villonodular synovitis, 3 patients with gout, one with synovial tuberculosis and one with a hemangioma of synovial membrane. Arthroscopy serves for early recognition of degeneration of hyalin cartilage and meniscal lesions, while synovial biopsies are also largely non-traumatic. Endoscopic evaluation of synovial membrane is more difficult. Mechanical irritation produces proliferation of synovial villi, while bacterial and rheumatoid inflammation leads to exudative and necrotic changes. The differences are obvious in marked inflammation but difficult to recognize in the beginning of any process. Arthroscopic and histological examination determines the etiology of synovitis only in pigmented villonodular synovitis and synovial tuberculosis. In the other forms of synovitis it is only possible to determine the stage and intensity of inflammation but not the etiology. The diagnosis of rheumatoid arthritis in particular is seldom secured by arthroscopy.