Phonophoresis is a physical therapy modality that combines ultrasound with the topical application of pain medication. Types of drugs (when phonophoresis is used as a physical therapy modality) include local anesthetics such as lidocane, prescription NSAIDs and counter-irritants such as menthol.
In phonophoresis, the ultrasound enhances the conduction of the pain-relieving medication into your soft tissues for a deep penetration. The use of the ultrasound allows for a high concentration of the applied drug to reach the underlying muscles. The drug is also delivered to a larger surface area, in a dose that is considered by doctors to be therapeutic.
The nice thing about phonophoresis is that because the medication is applied to your skin (called transdermal drug delivery) you avoid the nasty side effects generally associated with taking pain pills by mouth, or having an injection: Irritation of stomach lining, pain and/or risk of infection.