Magnetic resonance imaging features of focal bone lesions secondary to therapeutic ultrasound diathermy

Therapeutic ultrasound diathermy is a widely available noninvasive method, used to softening scar tissue, resolving edema, and accelerating wound healing. However, there is no consensus regarding the efficacy of this method and there is a lack of information on specific complications. We report three cases of focal bone lesions time-related with physiotherapy using ultrasound diathermy. The first patient presented with lesions in the medial and lateral portions of the distal metaphysis of the right femur, as well as in the proximal metaphysis of the tibia. The second patient presented with lesions in the left ankle. The third patient presented with lesions in the knee, bilaterally. The lesions were characterized by subcortical linear or arc lesions with hypointense signal on T1-weighted imaging and hyperintense signal on T2- and proton-density weighted imaging, similar to osteonecrosis. However theses lesions were distributed in superficial areas, in which the ultrasound is directly applied. All patients reported improvement or resolution of pain after discontinuation of ultrasound diathermy. Therefore, therapeutic ultrasound diathermy may be associated with focal bone lesions. This diagnosis should be considered when superficial bone lesions appear time-related to therapy and in areas not usually affected by osteonecrosis.