The effect of low-intensity pulsed ultrasound on bone healing in SR-PLLA rod fixed experimental distal femur osteotomy in rat.

The effects of low-intensity pulsed ultrasound (30 mW/cm2) were investigated in experimental cancellous bone fracture healing in bioabsorbable self-reinforced poly-L-lactide (SR-PLLA) rod fixed distal femur osteotomy in rats. A transverse transcondylar osteotomy was fixed with one SR-PLLA rod in 32 male Wistar rats of the age of 20 weeks. Half of the rats had a daily 20-min ultrasound exposure for three weeks. The follow-up times were three, six, and 12 weeks. Radiographical, histological, microradiographical, oxytetracycline labeling, and histomorphometrical analyses were performed. No foreign-body reactions were noted. The biocompatibility of SR-PLLA and ultrasound was found to be good. In the radiological and histological assessments there was a slight tendency for enhanced healing in the ultrasound group at three weeks, but at six and 12 weeks no differences were observed. The histomorphometrical and oxytetracycline labeling analyses showed that ultrasound exposure had no significant effects on bone healing. The present study shows that there were no obvious findings to support the hypothesis that low-intensity pulsed ultrasound enhances bone healing in self-reinforced poly-L-lactide (SR-PLLA) rod fixed experimental metaphyseal distal femur osteotomy in rats. The observed good biocompatibility provides a safe starting-point for clinical trials on bioabsorbable fixation combined with low-intensity ultrasound.