Thank you very much colleagues for your input on this topic. It is clearly a debatable subject! I did decided not to use ultrasound in the end, mainly for the reason that I felt other therapies were more appropriate for this chronic pain pattern. I agree that it seems unlikely that any harm would come from a superficial therapeutic dose, however I do feel that even if there is a small chance of doing lasting damage , I would rather not use it.
Thank you again, Natasha