Effect of low-intensity pulsed ultrasound on fracture callus mineral density and flexural strength in rabbit tibial fresh fracture

Abstract

Low-intensity ultrasound is a biophysical intervention on a fracture repair process. However, the effect of low-intensity ultrasound therapy on fracture healing is controversial. The aim of the present study was to evaluate the effect of low-intensity pulsed ultrasound (LIPUS) therapy on the fracture healing process, including mineral density and strength of callus using a rabbit model. A total of 30 rabbits underwent unilateral, transverse, and mid-tibia open osteotomies that were stabilized with external fixators. Then, the animals were divided into two study groups composed of 15 rabbits each: the case group (US), which were exposed to low-intensity pulsed ultrasound with 30 mW/cm(2) intensity and 1.5 MHz sine waves; and the control group (C), which underwent sham ultrasound treatment. Callus development and mineral density were evaluated using multidetector computed tomography at 2, 5, and 8 weeks, after which the animals were killed. Three-point bending tests of both healed and intact bones were assessed and compared. The results demonstrated that the callus mineral density in the US group was higher than in the C group (1202.20 +/- 81.30 vs. 940.66 +/- 151.58 HU; P = 0.001) at the end of the 8th week. The mean recorded three-point bending test score of healed bones in the US group was not significantly different from that of the C group (359.35 +/- 173.39 vs. 311.02 +/- 80.58 N; P = 0.114). The present study showed that low-intensity pulsed ultrasound enhanced callus mineral density with an insignificant increase in the strength of the fractured bone.