title: Bone turnover and articular cartilage differences localized to subchondral cysts in knees with advanced osteoarthritis.
abstract: OBJECTIVE
  To investigate changes in bone structure, turnover, and articular cartilage localized in subchondral bone cyst (SBC) regions associated with knee osteoarthritis (OA).
  
  
  METHODS
  Tibial plateaus (n = 97) were collected from knee OA patients during total knee arthroplasty (TKA). SBCs were identified using micro-computed tomography, and the specimens were divided into non-cyst (n = 25) and bone cyst (n = 72) groups. Microstructure of subchondral bone was assessed using bone volume fraction (BV/TV), trabecular number (Tb.N), structure model index (SMI) and bone mineral density (BMD). In bone cyst group, the cyst subregion, which contained at least one cyst, and the peri-cyst subregion, which contained no cysts, were further selected for microstructure analysis. Articular cartilage damage was estimated using the Osteoarthritis Research Society International (OARSI) score. The numbers of TRAP(+) osteoclasts, Osterix(+) osteoprogenitors, Osteocalcin(+) osteoblasts and expression of SOX9 were evaluated by immunohistochemistry.
  
  
  RESULTS
  Bone cyst group presented higher BV/TV, Tb.N and SMI at subchondral bone than non-cyst group. Furthermore, cyst subregion displayed increased BV/TV and Tb.N but lower BMD and SMI than peri-cyst subregion. Histology revealed a higher OARSI score in bone cyst group. SBC exhibited a weak relationship with BV/TV, etc. The numbers of TRAP(+) osteoclasts, Osterix(+) osteoprogenitors, Osteocalcin(+) osteoblasts and expression of SOX9, were higher in bone cyst group.
  
  
  CONCLUSIONS
  SBCs within knee OA are characterized by focally increased bone turnover, altered bone structure and more severe articular cartilage damage. The increased bone turnover possibly contributes to altered bone structure localized in SBC areas, and thus aggravates articular cartilage degeneration.
authors.affiliation: Department of Orthopaedics and Traumatology, The University of Hong Kong, Hong Kong; Bone Bioengineering Laboratory, Department of Biomedical Engineering, Columbia University, New York, USA. Electronic address: cy003@hku.hk.
authors.forename: Y
authors.initials: Y
authors.lastname: Chen
authors.affiliation: Center for Human Tissue and Organs Degeneration and Shenzhen Key Laboratory of Marine Biomedical Materials, Shenzhen Institutes of Advanced Technology, CAS, China. Electronic address: wangting@siat.ac.cn.
authors.forename: T
authors.initials: T
authors.lastname: Wang
authors.affiliation: Center for Human Tissue and Organs Degeneration and Shenzhen Key Laboratory of Marine Biomedical Materials, Shenzhen Institutes of Advanced Technology, CAS, China. Electronic address: min.guan@siat.ac.cn.
authors.forename: M
authors.initials: M
authors.lastname: Guan
authors.affiliation: Department of Orthopaedics and Traumatology, The University of Hong Kong, Hong Kong. Electronic address: zhaoww@hku.hk.
authors.forename: W
authors.initials: W
authors.lastname: Zhao
authors.affiliation: Department of Orthopaedics and Traumatology, The University of Hong Kong, Hong Kong; Shenzhen Key Laboratory for Innovative Technology in Orthopaedic Trauma, The University of Hong Kong Shenzhen Hospital, China. Electronic address: klleunga@hkucc.hku.hk.
authors.forename: F-K-L
authors.initials: FK
authors.lastname: Leung
authors.affiliation: Center for Human Tissue and Organs Degeneration and Shenzhen Key Laboratory of Marine Biomedical Materials, Shenzhen Institutes of Advanced Technology, CAS, China. Electronic address: hb.pan@siat.ac.cn.
authors.forename: H
authors.initials: H
authors.lastname: Pan
authors.affiliation: Center for Human Tissue and Organs Degeneration and Shenzhen Key Laboratory of Marine Biomedical Materials, Shenzhen Institutes of Advanced Technology, CAS, China; Department of Orthopaedic Surgery, Johns Hopkins University School of Medicine, Baltimore, MD, USA. Electronic address: xcao11@jhmi.edu.
authors.forename: X
authors.initials: X
authors.lastname: Cao
authors.affiliation: Center for Human Tissue and Organs Degeneration and Shenzhen Key Laboratory of Marine Biomedical Materials, Shenzhen Institutes of Advanced Technology, CAS, China; Bone Bioengineering Laboratory, Department of Biomedical Engineering, Columbia University, New York, USA. Electronic address: exg1@columbia.edu.
authors.forename: X E
authors.initials: XE
authors.lastname: Guo
authors.affiliation: Department of Orthopaedics and Traumatology, The University of Hong Kong, Hong Kong; Center for Human Tissue and Organs Degeneration and Shenzhen Key Laboratory of Marine Biomedical Materials, Shenzhen Institutes of Advanced Technology, CAS, China; Shenzhen Key Laboratory for Innovative Technology in Orthopaedic Trauma, The University of Hong Kong Shenzhen Hospital, China. Electronic address: wwlu@hku.hk.
authors.forename: W W
authors.initials: WW
authors.lastname: Lu
mesh_terms: D000368:Aged; D019645:Arthroplasty, Replacement, Knee; D001845:Bone Cysts / Q000000981:diagnostic imaging* / Q000473:pathology; D015519:Bone Density; D016723:Bone Remodeling; D002358:Cartilage, Articular / Q000166:cytology / Q000000981:diagnostic imaging* / Q000473:pathology; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009929:Organ Size; D020370:Osteoarthritis, Knee / Q000000981:diagnostic imaging* / Q000473:pathology / Q000601:surgery; D010006:Osteoblasts / Q000166:cytology; D010010:Osteoclasts / Q000166:cytology; D013234:Stem Cells / Q000166:cytology; D013977:Tibia / Q000166:cytology / Q000000981:diagnostic imaging* / Q000473:pathology; D055114:X-Ray Microtomography
keywords: Articular cartilage; Bone remodeling; Bone structure; Osteoarthritis; Subchondral bone cyst