title: A collagenase gel/physical defect model for controlled induction of superficial digital flexor tendonitis.
abstract: BACKGROUND
  A consistent and clinically relevant model for the induction of core lesions confined to the mid-metacarpal superficial digital flexor tendon (SDFT) has not been previously reported. Injection of bacterial collagenase is commonly used but often results in large, irregular and inconsistent lesions that disrupt the superficial tendon layers and epitenon.
  
  
  OBJECTIVE
  To develop and evaluate a new injection technique for collagenase induction of SDFT injury.
  
  
  METHODS
  Collagenase gel was injected into a physical columnar defect created by longitudinally placing a curved 16 gauge 8.89 cm needle in the mid-metacarpal SDFT in a randomly selected forelimb of 10 horses. A placebo treatment injection was performed 1 week later. Serial ultrasound examinations were performed. Horses were subjected to euthanasia at 2 (n = 2), 4 (n = 2), 8 (n = 4) and 16 (n = 2) weeks post treatment injection. Post mortem magnetic resonance imaging and histological analysis were performed. Gene expression (18S, SCX, TNC, TNMD, COL1A1, COL3A1, COMP, DCN, MMP1, MMP3 and MMP13), total DNA, glycosaminoglycan and collagen content were determined for experimental tendons (n = 10) and unaffected tendons (n = 9).
  
  
  RESULTS
  Mid-metacarpal SDFT core lesion induction was successful in all tendons with consistent lesion cross-sectional area and minimal epitenon disruption. Histology confirmed loss of normal tendon architecture after tendonitis induction and subsequent healing of the tendon core lesion. Compared with gene expression in unaffected tendons, several tested genes were significantly upregulated (COL1A1, COL3A1, TNMD, SCX, TNC, MMP13), while others showed significant downregulation (COMP, DCN, and MMP3).
  
  
  CONCLUSIONS
  Compared with the previously used direct injection of collagenase, this injection technique was easily performed and induced more consistent lesions that were mid-metacarpal and did not disrupt the epitenon.
  
  
  CONCLUSIONS
  This model will allow for objective assessment of therapies for tendon regeneration in the mid-metacarpal SDFT prior to clinical trials and routine clinical application.
authors.affiliation: Clinical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, New York, USA.
authors.forename: A E
authors.initials: AE
authors.lastname: Watts
authors.forename: A J
authors.initials: AJ
authors.lastname: Nixon
authors.forename: A E
authors.initials: AE
authors.lastname: Yeager
authors.forename: H O
authors.initials: HO
authors.lastname: Mohammed
mesh_terms: D000818:Animals; D017364:Collagenases / Q000008:administration & dosage / Q000633:toxicity*; D005260:Female; D005552:Forelimb; D005782:Gels; D006734:Horse Diseases / Q000139:chemically induced* / Q000473:pathology; D006736:Horses / Q000293:injuries*; D008297:Male; D012313:RNA; D060888:Real-Time Polymerase Chain Reaction; D052256:Tendinopathy / Q000139:chemically induced / Q000662:veterinary*; D013710:Tendons / Q000187:drug effects / Q000473:pathology; D013997:Time Factors
chemical_list: D005782:Gels; D012313:RNA; D017364:Collagenases