title: Low-intensity pulsed ultrasound accelerates fracture healing by stimulation of recruitment of both local and circulating osteogenic progenitors.
abstract: We investigated the effect of low-intensity pulsed ultrasound (LIPUS) on the homing of circulating osteogenic progenitors to the fracture site. Parabiotic animals were formed by surgically conjoining a green fluorescent protein (GFP) mouse and a syngeneic wild-type mouse. A transverse femoral fracture was made in the contralateral hind limb of the wild-type partner. The fracture site was exposed to daily LIPUS in the treatment group. Animals without LIPUS treatment served as the control group. Radiological assessment showed that the hard callus area was significantly greater in the LIPUS group than in the control group at 2 and 4 weeks post-fracture. Histomorphometric analysis at the fracture site showed a significant increase of GFP cells in the LIPUS group after 2 weeks (7.5%), compared to the control group (2.4%) (p < 0.05). The LIPUS group exhibited a significantly higher percentage of GFP cells expressing alkaline phosphatase (GFP/AP) than the control group at 2 weeks post-fracture (5.9%, 0.3%, respectively, p < 0.05). There was no significant difference in the percentage of GFP/AP cells between the LIPUS group (2.0%) and the control group (1.4%) at 4 weeks post-fracture. Stromal cell derived factor-1 and CXCR4 were immunohistochemically identified at the fracture site in the LIPUS group. These data indicate that LIPUS induced the homing of circulating osteogenic progenitors to the fracture site for possible contribution to new bone formation.
authors.affiliation: Department of Orthopaedic Surgery, Yokohama City University, Yokohama, Japan. kumagai@yokohama-cu.ac.jp
authors.forename: Ken
authors.initials: K
authors.lastname: Kumagai
authors.forename: Ryohei
authors.initials: R
authors.lastname: Takeuchi
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Ishikawa
authors.forename: Yuichiro
authors.initials: Y
authors.lastname: Yamaguchi
authors.forename: Takahiro
authors.initials: T
authors.lastname: Fujisawa
authors.forename: Takashi
authors.initials: T
authors.lastname: Kuniya
authors.forename: Shu
authors.initials: S
authors.lastname: Takagawa
authors.forename: George F
authors.initials: GF
authors.lastname: Muschler
authors.forename: Tomoyuki
authors.initials: T
authors.lastname: Saito
mesh_terms: D053687:Adult Stem Cells / Q000502:physiology; D000818:Animals; D005264:Femoral Fractures / Q000000981:diagnostic imaging / Q000473:pathology / Q000628:therapy*; D005269:Femur / Q000473:pathology; D017102:Fracture Healing / Q000528:radiation effects*; D007150:Immunohistochemistry; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D010012:Osteogenesis; D011859:Radiography; D014464:Ultrasonic Therapy