title: Histologic and histomorphometric evaluation of midcarpal joint defects in Thoroughbreds raised with and without early conditioning exercise.
abstract: OBJECTIVE
  To describe and measure histologic features of midcarpal joint cartilage defects in Thoroughbreds and evaluate the influence of early conditioning exercise on defect development.
  
  
  METHODS
  24 midcarpal joints from twelve 18-month-old Thoroughbreds.
  
  
  METHODS
  Midcarpal joints from 12 horses (6 exercised spontaneously at pasture only and 6 given additional conditioning exercise beginning at a mean age of 3 weeks were evaluated. Gross cartilage defects were assessed histologically. Third and radial carpal bones were categorized with regard to the presence or absence of calcified cartilage (CC) abnormalities at the dorsoproximal and dorsodistal articular surfaces, respectively; histomorphometric assessment and statistical analysis were conducted for the third carpal bone.
  
  
  RESULTS
  Number and severity of defects did not appear different between exercise groups. Nine third or radial carpal bones had thickened CC with microcracks, matrix and osteochondral junction changes, and increased vascularity, without histologic changes in the hyaline cartilage. Third carpal bones with CC abnormalities had significantly thicker CC (452 vs 228 μm) than did those without CC abnormalities in the evaluated region. However, in the same region, there were no significant differences in hyaline cartilage thickness (681 vs 603 μm), vascular channel area in the subchondral bone (624,894 vs 490,320 μm(2)), or number of vascular channels (15.9 vs 18.0).
  
  
  CONCLUSIONS
  Early exercise did not appear to influence the distribution or severity of cartilage defects in the midcarpal joint. Calcified cartilage abnormalities beneath the undisrupted hyaline cartilage in the dorsoproximal aspect of the third carpal bone may represent the first changes in the pathogenesis of midcarpal osteochondral disease.
authors.affiliation: Tissue Mechanics Laboratory, Department of Chemical and Materials Engineering, Faculty of Engineering, University of Auckland, Auckland 1142, New Zealand.
authors.forename: Woong
authors.initials: W
authors.lastname: Kim
authors.forename: Chris E
authors.initials: CE
authors.lastname: Kawcak
authors.forename: C Wayne
authors.initials: CW
authors.lastname: McIlwraith
authors.forename: Elwyn C
authors.initials: EC
authors.lastname: Firth
authors.forename: Neil D
authors.initials: ND
authors.lastname: Broom
mesh_terms: D000818:Animals; D002357:Cartilage Diseases / Q000209:etiology / Q000473:pathology / Q000662:veterinary*; D005552:Forelimb / Q000473:pathology; D006734:Horse Diseases / Q000473:pathology*; D006736:Horses; D007592:Joint Diseases / Q000209:etiology / Q000473:pathology / Q000662:veterinary*; D010805:Physical Conditioning, Animal / Q000009:adverse effects*