Pulsed Focused Ultrasound Treatment of Muscle Mitigates Paralysis-Induced Bone Loss in the Adjacent Bone: A Study in a Mouse Model

Bone loss can occur following bed rest, space flight, spinal cord injury, or age-related hormonal changes. The treatment methods for this condition include pharmaceutical interventions and exercise, neither of which is particularly effective. Other technologies include low intensity pulsed ultrasound targeted to the bone, used previously to enhance fracture healing, and whole body vibration. This study attempted to mitigate paralysis-induced bone loss indirectly, by applying pulsed focused ultrasound (pFUS) to the midbelly of a paralyzed muscle. We employed a mouse model of disuse that utilizes onabotulinumtoxin A, which induces rapid bone loss in 5 days. The pFUS treatments were performed daily for four consecutive days following paralysis. A spherically focused 2-MHz transducer produced 5-microsecond pulses at pulse repetition frequency mimicking motor neuron firing rates during walking (80 Hz) or standing (20 Hz). Two different power levels were used corresponding to peak positive focal pressures of 30 and 18 MPa. The trabecular bone changes were characterized using micro computed tomography. Our results indicated that application of pFUS at pulse repetition frequency of 20 Hz and lower amplitude setting successfully mitigated paralysis-induced bone loss. The targeted muscle tissue did not display any sign of injury. [Work supported by CDMRP SCIRP (SC090510).]