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Low-intensity transosseous ultrasound accelerates osteotomy healing in a sheep fracture model.

BACKGROUND
Low-intensity transcutaneous ultrasound can accelerate and augment the fracture-healing process. The aim of this study was to investigate the effect of transosseous application of low-intensity ultrasound on fracture-healing in an animal model.


METHODS
A midshaft osteotomy of the left tibia was performed in forty sheep. An external fixator was used to stabilize the osteotomy site. A thin stainless-steel pin was inserted into the bone, 1.0 cm proximal to the osteotomy site. Ultrasound was transmitted through the free end of this pin, with a PZT-4D transducer. In twenty animals, the treated limb received a 200-microsec burst of 1-MHz sine waves repeated at 1 kHz with an average intensity of 30 mW/cm(2) for twenty minutes daily. Twenty other animals underwent the same surgery but did not receive the ultrasound (controls). Animals were killed at seventy-five and 120 days postoperatively. Radiographic evaluation was performed every fifteen days. Mechanical testing and quantitative computed tomography were performed after death.


RESULTS
Fractures treated with ultrasound healed significantly more rapidly, as assessed radiographically, than did the controls (seventy-nine compared with 103 days, p = 0.027). On day 75, the mean cortical bone mineral density (and standard deviation) was 781 +/- 52 mg/mL in the treated limbs compared with 543 +/- 44 mg/mL in the control group (p = 0.014), and the average ultimate strength (as assessed with a lateral bending test) was 1928 +/- 167 N in the treated limbs compared with 1493 +/- 112 N in the control group (p = 0.012). No significant differences were noted on day 120.


CONCLUSIONS
This study demonstrated that low-intensity transosseous ultrasound can significantly accelerate the fracture-healing process, increase the cortical bone mineral density, and improve lateral bending strength of the healing fracture in a sheep osteotomy model.