title: Intramembranous ossification mechanism for bone bridge formation at the growth plate cartilage injury site.
abstract: Salter's type III and type IV growth plate injuries often induce bone bridge formation at the injury site. To understand the cellular mechanisms, this study characterized proximal tibial transphyseal injury in rats. Histologically, bony bridge trabeculae appeared on day 7, increased on day 10, and became well-constructed on day 14 with marrow. Prior to and during bone bridging, there was no cartilage proteoglycan metachromatic staining and no collagen-X immunostaining at the injury site, nor was there any up-regulation of BrdU-labelled chondrocyte proliferation at the adjacent physeal cartilage, suggesting no new cartilage formation at the injury site. However, infiltration of vimentin-immunopositive mesenchymal cells from metaphysis and epiphysis was apparent on day 3, with the mesenchymal population being prominent on days 7 and 10 and subsided on day 14. Among these infiltrates were osteoprogenitor precursors expressing osteoblast differentiation factor (cbf-alpha1) on day 3, along with some cbf-alpha1+ osteoblast-like cells lining bone trabeculae on days 7 and 10. Some mesenchymal cells and trabecula-lining cells were also alkaline phosphatase-immunopositive, further suggesting their osteoblast differentiation. From day 7 onwards, some trabecula-lining cells became osteocalcin-producing mature osteoblasts. These results suggest that bone bridge formation after growth plate injury occurs directly via intramembranous ossification through recruitment of marrow-derived osteoprogenitor cells.
authors.affiliation: Department of Orthopaedic Surgery, and University of Adelaide Department of Paediatrics, Women's and Children's Hospital, 72 King William Road, North Adelaide 5006, Australia. cory.xian@adelaide.edu.au
authors.forename: Cory J
authors.initials: CJ
authors.lastname: Xian
authors.forename: Fiona H
authors.initials: FH
authors.lastname: Zhou
authors.forename: Rosa C
authors.initials: RC
authors.lastname: McCarty
authors.forename: Bruce K
authors.initials: BK
authors.lastname: Foster
mesh_terms: D000818:Animals; D001861:Bone Regeneration / Q000502:physiology*; D002356:Cartilage / Q000293:injuries / Q000378:metabolism* / Q000473:pathology; D002454:Cell Differentiation; D002465:Cell Movement; D019902:Chondrocytes / Q000378:metabolism / Q000473:pathology; D004195:Disease Models, Animal; D006132:Growth Plate / Q000473:pathology / Q000502:physiology*; D006614:Hindlimb; D007150:Immunohistochemistry; D008297:Male; D059630:Mesenchymal Stem Cells / Q000378:metabolism / Q000473:pathology; D010006:Osteoblasts / Q000378:metabolism / Q000473:pathology; D015675:Osteocalcin / Q000378:metabolism; D010012:Osteogenesis / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D000072042:Salter-Harris Fractures; D013977:Tibia / Q000293:injuries / Q000473:pathology / Q000502:physiology*; D014746:Vimentin / Q000378:metabolism
chemical_list: D014746:Vimentin; D015675:Osteocalcin