title: Mesenchymal stem cells in synovial fluid increase after meniscus injury.
abstract: BACKGROUND
  Although relatively uncommon, spontaneous healing from a meniscus injury has been observed even within the avascular area. This may be the result of the existence of mesenchymal stem cells in synovial fluid.
  
  
  OBJECTIVE
  The purpose of this study was to investigate whether mesenchymal stem cells existed in the synovial fluid of the knee after meniscus injury.
  
  
  METHODS
  Synovial fluid was obtained from the knees of 22 patients with meniscus injury just before meniscus surgery and from 8 volunteers who had no history of knee injury. The cellular fraction of the synovial fluid was cultured for 14 days followed by analysis for multilineage potential and presentation of surface antigens characteristic of mesenchymal stem cells. Colony-forming efficiency and proliferation potential were also compared between the two groups.
  
  
  RESULTS
  Cells with characteristics of mesenchymal stem cells were observed in the synovial fluid of injured knees to a much greater degree than in uninjured knees. The colony-forming cells derived from the synovial fluid of the knee with meniscus injury had multipotentiality and surface epitopes identical to mesenchymal stem cells. The average number of colony formation, obtained from 1 mL of synovial fluid, in meniscus-injured knees was 250, higher than that from healthy volunteers, which was 0.5 (p < 0.001). Total colony number per synovial fluid volume was positively correlated with the postinjury period (r = 0.77, p < 0.001).
  
  
  CONCLUSIONS
  Mesenchymal stem cells were found to exist in synovial fluid from knees after meniscus injury. Mesenchymal stem cells were present in higher numbers in synovial fluid with meniscus injury than in normal knees. Total colony number per synovial fluid volume was positively correlated with the postinjury period.
  
  
  CONCLUSIONS
  Our current human study and previous animal studies suggest the possibility that mesenchymal stem cells in synovial fluid increase after meniscus injury contributing to spontaneous meniscus healing.
authors: Department of Joint Surgery and Sports Medicine, Graduate School, Tokyo Medical and Dental University, Tokyo, Japan.
authors: Yu
authors: Y
authors: Matsukura
authors: Takeshi
authors: T
authors: Muneta
authors: Kunikazu
authors: K
authors: Tsuji
authors: Hideyuki
authors: H
authors: Koga
authors: Ichiro
authors: I
authors: Sekiya
mesh_terms: D000293:Adolescent; D000328:Adult; D015415:Biomarkers / Q000378:metabolism; D016022:Case-Control Studies; D019070:Cell Lineage; D049109:Cell Proliferation; D002478:Cells, Cultured; D002648:Child; D000939:Epitopes; D006801:Humans; D007718:Knee Injuries / Q000276:immunology / Q000378:metabolism / Q000473:pathology* / Q000601:surgery; D008592:Menisci, Tibial / Q000276:immunology / Q000378:metabolism / Q000473:pathology* / Q000601:surgery; D059630:Mesenchymal Stem Cells / Q000276:immunology / Q000378:metabolism / Q000473:pathology*; D008875:Middle Aged; D013582:Synovial Fluid / Q000166:cytology* / Q000276:immunology / Q000378:metabolism; D000070600:Tibial Meniscus Injuries; D013997:Time Factors; D015854:Up-Regulation; D014945:Wound Healing; D055815:Young Adult
chemical_list: D015415:Biomarkers; D000939:Epitopes