Corrections
===========


The following article was originally published with an incorrect digital object identifier (doi): Song IH, Althoff CE, Hermann KG, Scheel AK, Knetsch T, Schoenharting M, *et al*. Knee osteoarthritis. Efficacy of a new method of contrast-enhanced musculoskeletal ultrasonography in detection of synovitis in patients with knee osteoarthritis in comparison with magnetic resonance imaging. *Ann Rheum Dis* 2008;**67**:19-25. It has been updated with the correct doi: 10.1136/ard.2007.067462. We apologise for any inconvenience caused.