An objective assessment of synovitis of the knee: measurement of the size of the suprapatellar pouch on xeroradiography.

Measurement of the size of the suprapatellar pouch of the knee appears to be a simple, useful, objective, and reproducible assessment of synovitis of the knee. Changes in the apparent size of the suprapatellar pouch have been shown to correlate closely with the volume of synovial fluid aspirated from the knee and with changes in circumferential measurements. Aspiration of 20 ml of fluid will produce a change in size significant at the 1% level. Lateral xeroradiographs were used in this study, as soft-tissue planes are more closely defined on xeroradiographs than on standard radiographs.