Ultrasound Enhances Recombinant Human BMP-2 Induced Ectopic Bone Formation in a Rat Model

Abstract

Two methods to improve bone repair include the use of recombinant human bone morphogenetic protein-2 (rhBMP-2) and low-intensity pulsed ultrasound (LIPUS). The present study was designed to determine if LIPUS enhances the effect of rhBMP-2–induced bone formation in a well characterized ectopic implant model. Absorbable collagen sponges loaded with 0-, 1-, 2.5- or 5-μg doses of rhBMP-2 were implanted subcutaneously in 11-week-old, male Long Evans rats, followed by daily 20-min LIPUS or sham LIPUS treatment beginning 1 d after surgery. Explanted sponges were assessed for bone volume, mineral density and mineral content by microcomputed tomography (μCT). At two weeks, LIPUS had no effect on rhBMP-2–induced bone formation, but at four weeks, LIPUS increased bone volume in the 1-μg rhBMP-2–treated implants 117.7-fold (0.02 ± 0.04 mm 3 vs. 2.07 S.E.M. ± 1.67 mm 3; p = 0.028), and 2.3-fold in the 5-μg dose implants (5.96 ± 3.68 mm 3 vs. 13.52 ± 6.81 mm 3; p = 0.077) compared with sham LIPUS. Bone mineral density was not affected by LIPUS treatment. Total mineral content followed the same pattern as bone volume. Histologic staining for mineralized tissue was consistent with the μCT observations. The present study is the first to demonstrate that LIPUS enhances bone formation induced by rhBMP-2. (E-mail: robert_leven@rush.edu)