An apparatus (10) for ultrasonically treating an injury in conjunction with an orthopaedic cast (288) is disclosed. The apparatus includes a portable self-contained main operating unit (12), a support fixture (110, 520, 590, 610, 632, 672, 708, 824), an ultrasonic transducer treatment head module (14), and casting material for attaching the support fixture (110, 520, 590, 610, 632, 672, 708, 824) to the orthopaedic cast (288). The support fixture (110, 520, 590, 610, 632, 672, 708, 824) is configured and adapted for attachment to the orthopaedic cast (288) adjacent an external site corresponding to an internal injury remote from the main operating unit (12). The support fixture (110, 520, 590, 610, 632, 672, 708, 824) has a body (114) and at least one mesh projection (112, 526) extending from the body (114). The ultrasonic transducer treatment head module (14) is operatively connected to the main operating unit (12) and detachably engaged with the body (114) of the support fixture (110, 520, 590, 610, 632, 672, 708, 824). At least a portion of the casting material impregnates the mesh projection (112) to attach the support fixture (110, 520, 590, 610, 632, 672, 708, 824) to the cast (288).