title: Repair process after fibrocartilaginous enthesis drilling: histological study in a rabbit model.
abstract: BACKGROUND
  Disorders of the enthesis are often a consequence of sports injuries. However, there is uncertainty regarding the process of mechanical stress-related injuries at the enthesis and the subsequent repair process of the injured tissues. To elucidate the repair process of the fibrocartilaginous enthesis, we studied the repair of injured fibrocartilaginous enthesis and the morphological characteristics of the repaired tissue.
  
  
  METHODS
  We drilled 0.5-mm holes in the right tibial insertion of the patellar tendon of Japanese white rabbits, with their own left sides serving as controls. Specimens harvested at 1, 2, 4, 6, 8, and 12 weeks were examined histologically. Morphologically, the ratios of calcified fibrocartilage-bone interface lengths to enthesial lengths were compared between the control and surgical groups.
  
  
  RESULTS
  Repair initiation was observed in the deep bone layer at 1 week, with remarkable progress at 2 weeks. Repair at the enthesis and neoosteogenesis in deep bone layers were detected at 4 weeks, and the drill hole disappeared at 6 weeks. The tendon was partially invaded by fibrocartilage-covered chondroid bone at 8 weeks, and regenerated fibrocartilaginous enthesis and increased calcified fibrocartilage-bone interface irregularity was identified at 12 weeks. The ratios of calcified fibrocartilage-bone interface lengths to enthesial lengths were significantly greater in the surgical group than in the control group.
  
  
  CONCLUSIONS
  Repair progressed from bone to fibrocartilage and ended at fibrous tissue. Cancellous bone disruption triggered repair in all layers. Removal of the subchondral plate enabled infiltration of nutrients via blood vessels, with the underlying bone acting as a scaffold for the regenerating fibrocartilage.
authors.affiliation: Department of Orthopaedic Surgery, Nara Medical University, Kashihara-shi, Nara, 634-8522, Japan.
authors.forename: Koji
authors.initials: K
authors.lastname: Hayashi
authors.forename: Tsukasa
authors.initials: T
authors.lastname: Kumai
authors.forename: Ichiro
authors.initials: I
authors.lastname: Higashiyama
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Shinohara
authors.forename: Takenori
authors.initials: T
authors.lastname: Matsuda
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Takakura
mesh_terms: D000818:Animals; D001265:Athletic Injuries; D016022:Case-Control Studies; D004195:Disease Models, Animal; D051445:Fibrocartilage / Q000293:injuries* / Q000502:physiology; D008297:Male; D017847:Patellar Ligament / Q000293:injuries* / Q000502:physiology; D011817:Rabbits; D012216:Rheumatic Diseases / Q000503:physiopathology; D014945:Wound Healing / Q000502:physiology*