[Knee synovitis in a rheumatoid patient with separated joint cavity]

A 40-year-old female patient with seropositive rheumatoid arthritis of 10 years duration. She had performed a total knee replacement of her left knee. At surgery the suprapatellar pouch was found to be separate from the rest of the knee joint, where direct access to the articular collagenous tissue remained. The suprapatellar pouch, presumable separate from the knee cavity since birth, was free of disease. The rest of the knee joint had gross and histopathological evidence of severe rheumatoid synovitis. The sparing of this suprapatellar pouch by rheumatoid disease is not easily explained, but the finding of this case suggests that synovium and articular collagenous tissues are requisites of chronic rheumatoid arthritis.