The effect of low intensity pulsed ultrasound applied to rabbit tibiae during the consolidation phase of distraction osteogenesis.

The purpose of this study was to determine if low intensity pulsed ultrasound (LIPU) accelerated the maturation of regenerate bone when applied after distraction in a rabbit model. A mid-tibial osteotomy was performed in 26 New Zealand white rabbits and an external fixator applied anteromedially. After a seven day latency period, the tibiae were distracted 0.5 mm every 12 h for 10 days. Thirteen of the rabbits received LIPU for 20 min/day (treatment group) and 13 received sham LIPU (control group) from day 17 until sacrifice on day 37. Radiographs were taken weekly after distraction and the total and mineralized areas of the callus were measured. After sacrifice, dual-energy X-ray absorptiometry, torsional testing to failure, and histomorphometry were performed. Ultrasound-treated tibiae were a mean of 68.8 +/- 3.8% as stiff as and 68.2 +/- 6.0% as strong as the contralateral tibiae. Control tibiae were 78.7 +/- 7.0%, as stiff as and 70.2 +/- 7.9% as strong as the contralateral tibiae. The differences in stiffness and strength were not significant (p = 0.39 and 0.81, respectively) with the number of the animals tested in the study. The treatment group was 91.6% as dense as the contralateral side and the control group was 88.5% as dense as the contralateral side (p = 0.84). Radiographs revealed a significantly larger callus in the LIPU-treated tibiae at 1, 2 and 3 weeks after distraction compared to control tibiae (p < 0.01, 0.008 and 0.05, respectively). Histomorphometry revealed significantly less fibrous tissue in the LIPU-treated tibiae (p < 0.05) and a strong trend towards more bone in the LIPU-treated tibiae compared to controls (p = 0.06). LIPU was found to increase the size of the distraction callus and it might alter the composition of regenerate bone but it did not have a positive effect on the mechanical properties or density of regenerate bone when applied during the consolidation phase of distraction osteogenesis.