As far as I am aware, from studying a unit on Electrophysical Agents at uni- the evidence for ultrasound (and most electrophysical modalities) is sketchy at best because of the large range of variables involved. The main variables which were is question over is ideal frequency and duration- there has not been enough research controlling these variables (so that studies can be compared or added to existing study results) or enough participants in research conducted to come to strong conclusions.
However there appears to be good anecdotal/clinical use of ultrasound in acute situations such as medial meniscus tears and so it is still used.
---------- Post added at 08:40 PM ---------- Previous post was at 08:37 PM ----------
Also I found this article:
ScienceDirect.com - Archives of Physical Medicine and Rehabilitation - Efficacy of therapeutic ultrasound treatment of a meniscus tear in a severely disabled patient: a case report