Investigation of rat bone fracture healing using pulsed 1.5 MHz, 30 mW/cm(2) burst ultrasound--axial distance dependency.
This study investigated the effect of LIPUS on fracture healing when fractures were exposed to ultrasound at three axial distances: z=0 mm, 60 mm, and 130 mm. We applied LIPUS to rat fracture at these three axial distances mimicking the exposure condition of human fractures at different depths under the soft tissue. Measurement of LIPUS shows pressure variations in near field (nearby transducer); uniform profile was found beyond it (far field). We asked whether different positions of the fracture within the ultrasound field cause inconsistent biological effect during the healing process. Closed femoral fractured Sprague-Dawley rats were randomized into control, near-field (0mm), mid-near field (60 mm) or far-field (130 mm) groups. Daily LIPUS treatment (plane, but apodized source, see details in the text; 2.2 cm in diameter; 1.5 MHz sine waves repeating at 1 kHz PRF; spatial average temporal average intensity, ISATA=30 mW/cm(2)) was given to fracture site at the three axial distances. Weekly radiographs and endpoint microCT, histomorphometry, and mechanical tests were performed. The results showed that the 130 mm group had the highest tissue mineral density; and significantly higher mechanical properties than control at week 4. The 60 mm and 0 mm groups had significantly higher (i.e. p<0.05) woven bone percentage than control group in radiological, microCT and histomorphometry measurements. In general, LIPUS at far field augmented callus mineralization and mechanical properties; while near field and mid-near field enhanced woven bone formation. Our results indicated the therapeutic effect of LIPUS is dependent on the axial distance of the ultrasound beam. Therefore, the depth of fracture under the soft tissue affects the biological effect of LIPUS. Clinicians have to be aware of the fracture depth when LIPUS is applied transcutaneously.
Department of Orthopaedics and Traumatology, The Chinese University of Hong Kong, Shatin, Hong Kong, China.
Chak-Hei
CH
Fung
Department of Orthopaedics and Traumatology, The Chinese University of Hong Kong, Shatin, Hong Kong, China; Institute of Biomedical and Health Engineering, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen, People's Republic of China. Electronic address: louis@ort.cuhk.edu.hk.
Wing-Hoi
WH
Cheung
Orthopaedic Trauma and Clinical Therapies, Smith and Nephew, Inc., Durham, NC 27703, United States.
Neill M
NM
Pounder
Orthopaedic Trauma and Clinical Therapies, Smith and Nephew, Inc., Durham, NC 27703, United States.
F Javier
FJ
de Ana
Orthopaedic Trauma and Clinical Therapies, Smith and Nephew, Inc., Durham, NC 27703, United States.
Andrew
A
Harrison
Department of Orthopaedics and Traumatology, The Chinese University of Hong Kong, Shatin, Hong Kong, China; Institute of Biomedical and Health Engineering, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen, People's Republic of China.
Kwok-Sui
KS
Leung
D000818:Animals; D005260:Female; D005264:Femoral Fractures / Q000000981:diagnostic imaging / Q000503:physiopathology* / Q000628:therapy*; D005269:Femur / Q000000981:diagnostic imaging / Q000503:physiopathology* / Q000528:radiation effects*; D017102:Fracture Healing / Q000528:radiation effects*; D019220:High-Energy Shock Waves; D051381:Rats; D017207:Rats, Sprague-Dawley; D016896:Treatment Outcome; D014464:Ultrasonic Therapy / Q000379:methods*; D014463:Ultrasonography
Far field; Fracture healing; LIPUS; Ultrasound