title: The effect of intralesional injection of bone marrow derived mesenchymal stem cells and bone marrow supernatant on collagen fibril size in a surgical model of equine superficial digital flexor tendonitis.
abstract: BACKGROUND
  Collagen fibril size is decreased in repair tissue following tendon injury compared to normal tendon matrix in horses. Mesenchymal stem cells have been suggested to promote regeneration of tendon matrix rather than fibrotic repair following injury, although this concept remains unproven.
  
  
  OBJECTIVE
  To explore the hypothesis that implantation of autologous mesenchymal stem cells derived from bone marrow into a surgically created central core defect in the superficial digital flexor tendon (SDFT) of horses would induce the formation of a matrix with greater ultrastructural similarities to tendon matrix than the fibrotic scar tissue formed in control defects.
  
  
  METHODS
  Tissue was collected 16 weeks after induction of injury and 12 weeks after treatment from normal and injured regions of control and treated limbs of 6 horses and examined using transmission electron microscopy. Collagen fibril diameters were measured manually with image analysis software and surface areas calculated. Three parameters assessed for normal and injured tissue were mass average diameter (MAD), collagen fibril index (CFI) and the area dependent diameter (ADD).
  
  
  RESULTS
  Normal regions from both treated and control limbs displayed higher MAD and CFI values, as well as a characteristic bimodal distribution in fibril size. Injured regions from both treated and control limbs displayed significantly lower MAD and CFI values, as well as a unimodal distribution in fibril size. There were no significant differences between treated and control limbs for any of the parameters assessed.
  
  
  CONCLUSIONS
  Intralesional injection of autologous bone marrow derived mesenchymal stem cells had no measurable effect on the fibril diameter of collagen in healing tissue in the SDFT of this experimental model 16 weeks after injury.
  
  
  CONCLUSIONS
  Favouring matrix regeneration over fibrotic repair may not be the mechanism by which autologous mesenchymal stem cells assist healing of tendon injury.
authors.affiliation: North Carolina State University, College of Veterinary Medicine, NC, USA.
authors.forename: C J
authors.initials: CJ
authors.lastname: Caniglia
authors.forename: M C
authors.initials: MC
authors.lastname: Schramme
authors.forename: R K
authors.initials: RK
authors.lastname: Smith
mesh_terms: D000818:Animals; D001854:Bone Marrow Cells / Q000502:physiology*; D003094:Collagen / Q000737:chemistry / Q000378:metabolism*; D005552:Forelimb; D006734:Horse Diseases / Q000209:etiology / Q000628:therapy*; D006736:Horses; D045164:Mesenchymal Stem Cell Transplantation / Q000662:veterinary*; D013708:Tendon Injuries / Q000628:therapy / Q000662:veterinary*; D014945:Wound Healing
chemical_list: D003094:Collagen