Anatomic separation of the suprapatellar pouch spares its involvement by rheumatoid synovitis in the knee

Synovectomy of the knee was performed in a 27-year-old female with seropositive rheumatoid arthritis of 6 years duration. At surgery the suprapatellar pouch was found to be separate from the rest of the knee joint, where direct access to articular collagenous tissues remained. The suprapatellar pouch, presumably separate from the knee cavity since birth, was free of disease. The rest of the joint lining, and synovium of the forefoot joints, that had been operated on at the same time, had gross and histological evidence of severe rheumatoid synovitis. The sparing of this suprapatellar pouch by rheumatoid disease is not easily explained, especially since its origin and nature are similar to other synovial parts of the knee that were actively involved. These latter areas had direct access to articular collagenous tissues. The findings of this case question the predilection of rheumatoid arthritis for synovium, and suggest that synovium and articular collagenous tissues are requisites of chronic rheumatoid arthritis.