Methods: A total of 72 male Wistar-Albino rats were randomly divided into three equal groups. To induce a rib fracture, right thoracotomy was performed under general anesthesia and a 0.5-cm segment was removed from the fourth and fifth ribs. After 24 h of surgery, low-intensity pulsed ultrasound was implemented according to the groups. Group 1 served as the control group for the observation of normal bone healing. Low-intensity pulsed ultrasound was applied at a dose of 20% (2 msn pulse-8 msn pause) 100 mW/cm2 and 50% (5 msn pulse-5 msn pause) 200 mW/cm2 for six min, respectively in Group 2 and Group 3. All subjects were followed for six weeks. Eight animals from each group were sacrificed at two, four, and six weeks for further assessment. Histological alterations in the bone were examined.

Results: Although there was no statistically significant difference in osteoblasts, osteoclasts, new bone formation, and lymphocyte count among the groups, histological consolidation was significantly increased by low-intensity pulsed ultrasound. While low-intensity pulsed ultrasound induced osteoblastic, osteoclastic, and new bone formation, it inhibited lymphocyte infiltration.

Conclusion: Low-intensity pulsed ultrasound, either at low or high doses, induced the histological consolidation of rib fractures and inhibited lymphocyte infiltration. This effect was more prominent in the long-term and at higher dose with increased daily and total administration time. We, therefore, believe that accelerating the natural healing process in patients with rib fractures would enable to treat more effectively in short-term.