The results of a study on the oxygen tension in 103 synovial fluids from knee joints are presented. The lowest tensions were found in synovial Kuids from patients with rheumatoid arthritis. In some cases it was found to be as low as 0 mmHg. The oxygen tension in synovial fluids from patients with osteoarthrosis and from those with traumatic joint exudates was considerably higher. The pH and pC0, were measured in all the cases. Significant correlation was found between pOz and pH, and between PO, and pC0,.In 1957, Bywaters (1) and Clark et a1 (2) described widespread obliterative endangitis in the synovial membrane from patients with rheumatoid arthritis. The author therefore found it reasonable to assume, that intra-articular oxygen tension might also be affected. Oxygen studies along with measurements of p H and pC0, have been carried out since the fall of 1966. MATERIALS AND METHODSA total of 103 synovial fluids from the knee joint? of 40 patients were obtained without complications.T h e patient material originated mainly from the Department of Physical Medicine, Odense Universit y Hospital. The samples were taken partly from hospitalized patients and partly from outpatients, and were not correlated with therapy. Diagnosis, (5) : 24 of the patients had classic rheumatoid arthritis and 5 had definite rheumatoid arthritis.Synovial fluid was obtained by aseptic puncture of the knee under local anesthesia. The specimens were collected in siliconized syringes and immediately cooled in ice water until the analyses were performed. The oxygen tensions were measured utilizing a Clark type microelectrode oxygen monitor PHA 928 A. and pH, using a Radiometer AME'.The analyses were carried out within approximately 2 hr. The error, which occurs in the time interval from aspiration until analysis, was studied in 4 cases. The results are given in Fig 1. It appears that the error resulting from a few hours delay in analyzing the sample is negligible. RESULTSOxygen tension in the synovial fluid from patients with osteoarthroses varied from 20 to 71 mmHg. As to synovial fluids from joints injured by trauma, the 4 exudates had comparatively high values, between 42 and 87 mmHg. The oxygen tension in a bursa from a patient with rheumatoid arthritis was 55 mmHg. Finally, an oxygen tension of 42 mmHg was observed 'Astrup Micro Equipment, Radiometer, Copenhagen.

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