Low Intensity Pulsed Ultrasound Accelerated Bone Remodeling during Consolidation Stage of Distraction Osteogenesis Chun Wai Chan, 1 Ling Qin, 1 Kwong Man Lee, 2 Ming Zhang, 3 Jack Chun Yiu Cheng, 1 Kwok Sui Leung 1 1 Department of Orthopaedics and Traumatology, The Chinese University of Hong Kong, Prince of Wales Hospital, Shatin, N.T., Hong Kong 2 Lee Hysan Clinical Research Laboratories, The Chinese University of Hong Kong, Prince of Wales Hospital, Shatin, N.T., Hong Kong 3 Jockey Club Rehabilitation Engineering Centre, The Hong Kong Polytechnic University, Kowloon, Hong Kong Received 27 September 2004; accepted 5 May 2005 Published online 18 November 2005 in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/jor.20015 ABSTRACT: Bone regeneration in distraction osteogenesis occurs under tensile stress with axial rhythmic distraction after osteotomy. In this study, we evaluated if the low intensity pulsed ultrasound (LIPUS) was also effective on enhancement of bone remodeling during consolidation stage of distraction osteogenesis. Open osteotomy of seventeen 18-week-old female New Zealand rabbit tibiae were performed. The distraction was applied with the rate of 1 mm per day. LIPUS (30 mW/cm 2 , 1.5 MHz) was delivered for 20 min per day during 4-week consolidation stage (n ¼ 10). The animals without treatment served as sham group (n ¼ 7). Plain X-ray, peripheral quantitative computational tomography (pQCT), and torsional test were performed. Results showed that smaller radiolucent interzone of LIPUS treatment group was gradually occupied by calcified tissue in plain X-ray at week 2. The bone mineral density (BMD) measured on radiographs increased by 9.18% in the LIPUS group. Bone mineral content (BMC), hard callus volume, and bone strength index (BSI) measured by pQCT were 83%, 116%, and 94%, respectively, in LIPUS group that were significantly greater than those of the controls. At the 4th week, LIPUS-treated callus showed the development of neocorticalization in the proximal and distal region. The BMC, hard callus volume, and BSI of LIPUS group decreased and was not significantly different from control. This was also confirmed by the maximum torque of LIPUS-treated callus (1424.2 Æ 457.3 N Á mm) obtained at week 4, which did not differ from that of the sham group (1968.8 Æ 895.1 N Á mm). In conclusion, the effective period of LIPUS treatment was at the initial stage of consolidation, with accelerated bone formation and remodeling. ß 2005 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 24:263–270, 2006 Keywords: low intensity pulsed ultrasound; distraction osteogenesis; consolidation; bone remodeling; pQCT INTRODUCTION Bone regeneration in the distraction osteogenesis is under tensile stress with axial rhythmic distraction after osteotomy. Bone lengthening using monolateral or circular fixation method is an effective surgical approach in managing difficult orthopedic conditions, such as bone deformity, bone shortening, and bone defects. 1–3 Normally, a distraction rate of 0.7–1.3 mm per day was found beneficial for distraction osteogen- esis in the rabbit tibial model 4–6 and, therefore, a distraction rate of 1 mm per day was adopted and recommended clinically, 7 followed by a sufficient latency period. 8 Complication was, however, reported due to delayed consolidation associated with long sufficient time for neocorticalization and bone maturation 9 and utilization of different lengthening methods. 10 JOURNAL OF ORTHOPAEDIC RESEARCH FEBRUARY 2006 263 Correspondence to: Kwok Sui Leung (Telephone: (852) 2632 2724; Fax: (852) 2637 7889; E-mail: ksleung@cuhk.edu.hk) ß 2005 Orthopaedic Research Society. Published by Wiley Periodicals, Inc.