Air or CO2 for knee arthrography?

Both air and carbon dioxide (CO2) have been advocated for use as the negative agent in double-contrast knee arthrography. In 39 patients examined, 40 knee arthrograms were obtained, using CO2 as the negative agent for 20 studies and room air in the other 20. In addition, the change in pH of the joint fluid was measured. Of the 20 patients in the CO2 group, 12 had pain, five of whom described it as severe. Of the 20 in the air group, two reported only moderate discomfort. Regardless of the gas used, the incidence of pain was directly related to the amount of decrease in pH. Air is believed superior to CO2 primarily because it produces less pain, persists in the joint longer (allowing for refilming), costs less, and is readily available.