title: Scanning electron microscopic examination of third metacarpal/third metatarsal bone failure surfaces in thoroughbred racehorses with condylar fracture.
abstract: OBJECTIVE
  To examine the fracture failure surfaces from Thoroughbred horses that had sustained a catastrophic condylar fracture.
  
  
  METHODS
  Bone specimens from the failure surface were obtained from 12 Thoroughbred racehorses with catastrophic injury and 2 non-racing horses with accidental long bone fracture.
  
  
  METHODS
  Bone specimens from the failure surface of each fracture were incubated with gold microspheres to label microcracks before examination at x50 to x60,000 using scanning electron microscopy. Microcracking at the failure surface was assessed using a visual analog scale.
  
  
  RESULTS
  Branching arrays or clusters of microcracks were seen over a range of magnifications in adapted subchondral bone in the distal end of the MC3/MT3 bone from racing Thoroughbreds with a catastrophic displaced condylar fracture. In the palmar/plantar region, microcracking was associated with the formation of an array of macroscopic cracks in the condylar groove. A different pattern of microcracking was seen in specimens of bone from distal metaphyseal and diaphyseal MC3/MT3 failure surfaces from Thoroughbred racehorses with catastrophic fracture and non-racing horses with an accidental diaphyseal long bone fracture. Few microcracks were seen and typically did not form branching arrays.
  
  
  CONCLUSIONS
  These data suggest that propagation of condylar fracture in Thoroughbred racehorses is initiated by the formation of nanoscale microcracks in adapted subchondral bone that form during exercise-induced bone adaptation.
  
  
  CONCLUSIONS
  Accumulation and coalescence of branching microcracks into arrays or clusters appears to eventually lead to the development of macroscopic subchondral cracks in the condylar groove and initiation of a condylar fracture.
authors.affiliation: Comparative Orthopaedic Research Laboratory, School of Veterinary Medicine, University of Wisconsin-Madison, Madison, WI 53706, USA.
authors.forename: Matthew W
authors.initials: MW
authors.lastname: Stepnik
authors.forename: Catherine L
authors.initials: CL
authors.lastname: Radtke
authors.forename: Mary C
authors.initials: MC
authors.lastname: Scollay
authors.forename: Philip E
authors.initials: PE
authors.lastname: Oshel
authors.forename: Ralph M
authors.initials: RM
authors.lastname: Albrecht
authors.forename: Elizabeth M
authors.initials: EM
authors.lastname: Santschi
authors.forename: Mark D
authors.initials: MD
authors.lastname: Markel
authors.forename: Peter
authors.initials: P
authors.lastname: Muir
mesh_terms: D000818:Animals; D002358:Cartilage, Articular / Q000293:injuries / Q000473:pathology; D005260:Female; D050723:Fractures, Bone / Q000473:pathology / Q000662:veterinary*; D050724:Fractures, Cartilage; D006736:Horses / Q000293:injuries* / Q000601:surgery; D008297:Male; D008663:Metacarpus / Q000293:injuries* / Q000473:pathology; D008682:Metatarsal Bones / Q000293:injuries* / Q000473:pathology; D008855:Microscopy, Electron, Scanning / Q000662:veterinary; D010805:Physical Conditioning, Animal; D017211:Treatment Failure