title: Abnormal subchondral bone microstructure following steroid administration is involved in the early pathogenesis of steroid-induced osteonecrosis.
abstract: Loss of bone microstructure integrity is thought to be related to osteonecrosis. But the relationship between the time when bone microstructure integrity loss appears and the onset of osteonecrosis has not yet been determined. Our study demonstrated abnormal changes of subchondral bone microstructure involved in the early pathogenesis of osteonecrosis.
  
  
  BACKGROUND
  Using a rabbit model, we investigated the changes of subchondral bone microstructure following steroid administration to identify the onset of abnormal bone microstructure development in steroid-induced osteonecrosis.
  
  
  METHODS
  Fifty-five adult female Japanese White rabbits (mean body weight 3.5 kg; mean age 24 months) were used and randomly divided among three time points (3, 7, and 14 days) consisting of 15 rabbits each, received a single intramuscular injection of methylprednisolone acetate (MP; Pfizer Manufacturing Belgium NV) at a dose of 4 mg/kg, and a control group consisting of 10 rabbits was fed and housed under identical conditions but were not given steroid injections. A micro-CT scanner was applied to detect changes in the trabecular region of subchondral bone of excised femoral head samples. Parameters including bone volume fraction (BV/TV), bone surface (BS), trabecular bone pattern factor (Tb.Pf), trabecular thickness/number/separation (Tb.Th, Tb.N, and Tb.Sp), and structure model index (SMI) were evaluated using the software CTAn (SkyScan). After micro-CT scans, bilateral femoral heads were cut in the coronal plane at a thickness of 4 μm. The sections were then stained with haematoxylin-eosin and used for the diagnosis of osteonecrosis and the rate of development of osteonecrosis.
  
  
  RESULTS
  The BV/TV, BS, Tb.Th and Tb.N demonstrated a time-dependent decline from 3, 7, and 14 days compared with the control group, while the Tb.Pf, Tb.Sp and SMI demonstrated an increase at 3, 7, and 14 days compared with the control group. For the histopathology portion, osteonecrosis was not seen 3 days after steroid treatment, but was present 7 days after treatment and was obvious 14 days after treatment. Furthermore, the rate of osteonecrosis appearing between 7 and 14 days was not significantly different. In addition, the presence and variation of BV/TV, BS, Tb.Pf, Tb.Th, Tb.N, and SMI demonstrated significant changes at 7 days compared with the control group except Tb.Sp (at 14 days) and this is the time when osteonecrosis is thought to occur in this model.
  
  
  CONCLUSIONS
  This study demonstrated that osteonecrosis in rabbits is chronologically associated with changes in subchondral bone microstructure.
authors.affiliation: Center for Human Tissues and Organs Degeneration, Shenzhen Institute of Advanced Technology, Chinese Academy of Science, Shenzhen, China. wldzzs@163.com.|Department of Orthopedic Surgery, People's Hospital of Hangzhou, Nanjing Medical University, Hangzhou, China. wldzzs@163.com.
authors.forename: L
authors.initials: L
authors.lastname: Wang
authors.affiliation: Institute of Biomedicine and Biotechnology, Shenzhen Institute of Advanced Technology, Chinese Academy of Science, Shenzhen, China.
authors.forename: L
authors.initials: L
authors.lastname: Zhang
authors.affiliation: Center for Human Tissues and Organs Degeneration, Shenzhen Institute of Advanced Technology, Chinese Academy of Science, Shenzhen, China.
authors.forename: H
authors.initials: H
authors.lastname: Pan
authors.affiliation: Department of Orthopedic Surgery, People's Hospital of Shenzhen, Jinan University Second College of Medicine, Shenzhen, China.
authors.forename: S
authors.initials: S
authors.lastname: Peng
authors.affiliation: Center for Human Tissues and Organs Degeneration, Shenzhen Institute of Advanced Technology, Chinese Academy of Science, Shenzhen, China.
authors.forename: X
authors.initials: X
authors.lastname: Zhao
authors.affiliation: Center for Human Tissues and Organs Degeneration, Shenzhen Institute of Advanced Technology, Chinese Academy of Science, Shenzhen, China. wwlu@hku.hk.|Department of Orthopaedics and Traumatology, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Pokfulam, China. wwlu@hku.hk.
authors.forename: W W
authors.initials: WW
authors.lastname: Lu
mesh_terms: D000818:Animals; D004195:Disease Models, Animal; D005260:Female; D005270:Femur Head / Q000000981:diagnostic imaging / Q000473:pathology; D005938:Glucocorticoids / Q000633:toxicity*; D021621:Imaging, Three-Dimensional / Q000379:methods; D008775:Methylprednisolone / Q000633:toxicity*; D010020:Osteonecrosis / Q000139:chemically induced* / Q000473:pathology; D011817:Rabbits; D055114:X-Ray Microtomography / Q000379:methods
chemical_list: D005938:Glucocorticoids; D008775:Methylprednisolone
keywords: Abnormal; Osteonecrosis; Rabbit; Steroid; Subchondral bone microstructure