Anti-inflammatory effects of ultrasound therapy: evidence for a major placebo effect.

The value of therapeutic ultrasound (US) for reducing inflammation was tested in a double-blind controlled study in 150 patients following surgical removal of impacted lower third molars. Facial swelling, trismus, pain and serum C-reactive protein (CRP) were significantly reduced in the US-treated groups and in a placebo group ('mock' US) compared with an untreated control group. The majority of the anti-inflammatory activity was attributable to the placebo effect, and the highest intensity of US (1.5 W.cm-2) was consistently less beneficial than the lower intensities (0.1 and 0.5 W.cm-2) and the mock US.