Knee effusions are usually not marked in OA. This person had a large effusion expanding the suprapatellar pouch, with positive balloon sign (fluctuance) and patellar tap, and OA with CPPD.
Reproduced with permission from: OARSI Online Primer. Edited by Henrotin Y, Hunter D, Kawaguchi H. 2012. Osteoarthritis Research Society International. (http://primer.oarsi.org).
