title: The embryogenesis of the equine femorotibial joint: The equine interzone.
abstract: BACKGROUND
  Articular cartilage regeneration is the focus and goal of considerable research effort. Since articular chondrocytes descend from a distinct cohort of progenitor cells located in embryonic nascent joints (interzones), establishing the timing of equine interzone formation is an essential first step towards understanding equine joint and articular cartilage development.
  
  
  OBJECTIVE
  To establish the time frame during which the equine femorotibial interzone forms.
  
  
  METHODS
  Descriptive anatomical study.
  
  
  METHODS
  Equine embryos were harvested at 37 (E37), 40, 42, 45, 50 and 65 days' gestation. The femorotibial interzone was examined using high-resolution episcopic microscopy of E37, E42, E45, E50 and E65. Additional histology and collagen-II-immunohistochemistry were performed on E42.
  
  
  RESULTS
  At E37, the femorotibial interzone is first visible as a uniform layer, while at E42 the interzone is fully formed and consists of 3 morphologically distinct layers. The first evidence of cavitation was seen at E45. At E50, the cruciate ligaments were well formed and by E65, joint formation appeared complete.
  
  
  CONCLUSIONS
  The embryogenesis of the equine femorotibial joint is similar to the developmental timeline of stage-matched human and murine embryos. Further studies looking at interzone formation on a cellular and molecular level may further our understanding of the intricate developmental patterns and pathways of articular cartilage development.
authors.affiliation: Equine Hospital, University of Veterinary Medicine Vienna, Austria.
authors.forename: F
authors.identifier: http://orcid.org/0000-0002-6977-1984
authors.initials: F
authors.lastname: Jenner
authors.affiliation: Department of Orthopaedics, Department of Otorhinolaryngology, Erasmus MC, University Medical Center Rotterdam, The Netherlands.
authors.forename: G J V M
authors.initials: GJ
authors.lastname: van Osch
authors.affiliation: Center for Anatomy and Cell Biology, Medical University of Vienna, Austria.
authors.forename: W
authors.initials: W
authors.lastname: Weninger
authors.affiliation: Center for Anatomy and Cell Biology, Medical University of Vienna, Austria.
authors.forename: S
authors.initials: S
authors.lastname: Geyer
authors.affiliation: Department of Equine Sciences, Faculty of Veterinary Medicine, Utrecht University, The Netherlands.
authors.forename: T
authors.initials: T
authors.lastname: Stout
authors.affiliation: Department of Equine Sciences, Faculty of Veterinary Medicine, Utrecht University, The Netherlands.
authors.forename: R
authors.initials: R
authors.lastname: van Weeren
authors.affiliation: Section Veterinary Clinical Sciences, School of Veterinary Medicine, University College Dublin, Ireland.
authors.forename: P
authors.initials: P
authors.lastname: Brama
mesh_terms: D000818:Animals; D006614:Hindlimb / Q000196:embryology*; D006736:Horses / Q000196:embryology*; D007596:Joints / Q000196:embryology*
keywords: articular cartilage; embryo; embryogenesis; horse; interzone; joint development