Ultrasound for the relief of joint and soft-tissue conditions has been used in manual medicine for many decades, however, its evidence base is flimsy. A recent snapshot summary of its effectiveness in the treatment of low back pain and peripheral joint problems has shown its benefits to be marginal (link: https://www.ncor.org.uk/cfrs/effectiveness-of-therapeutic-ultrasound/ ).
However, David does use TUS in practice for certain situations where it can enhance the other techniques he is applying. This may be in cases of tennis elbow, for example, where the lesion is relatively superficial. There is evidence showing it has physiological effects including increasing blood flow to an area and stimulating cells known as fibroblasts which play an important role in collagen production and repair.