Macroscopic changes in the distal ends of the third metacarpal and metatarsal bones of Thoroughbred racehorses with condylar fractures.
OBJECTIVE
To determine changes in the distal ends of the third metacarpal and metatarsal bones (MCIII and MTIII) of Thoroughbred racehorses that had sustained a catastrophic condylar fracture during high-speed exercise.


METHODS
Fractured and contralateral MCIIIs and MTIIIs from 11 Thoroughbred racehorses that sustained a displaced condylar fracture during racing, both MCIIIs from 5 Thoroughbred racehorses euthanatized because of a catastrophic injury other than a condylar fracture, and both MCIIIs from 5 horses of other breeds that had not been professionally trained or raced.


METHODS
Macroscopic observations were made of the distal ends of the bones before and after digestion of the articular cartilage with NaOH.


RESULTS
In all 11 racehorses with a displaced condylar fracture, the fracture was associated with a branching array of cracks in the condylar groove. In this region, fracture margins were smooth, and there was loss of subchondral bone. Comminution of the dorsal cortex was also seen. Parasagittal linear wear lines in the articular cartilage, erosions in the articular cartilage of the condyles, loss of the underlying subchondral bone, and cracking of condylar grooves were all more severe in the Thoroughbred racehorses than in the horses that had not been professionally trained or raced.


CONCLUSIONS
Results suggest that condylar fractures in horses are pathologic fatigue or stress fractures that arise from a preexisting, branching array of cracks in the condylar groove of the distal end of MCIII or MTIII.
D000818:Animals; D002358:Cartilage, Articular / Q000473:pathology; D005552:Forelimb / Q000473:pathology*; D050723:Fractures, Bone / Q000473:pathology / Q000662:veterinary*; D006734:Horse Diseases / Q000473:pathology*; D006736:Horses; D008297:Male; D050279:Metacarpal Bones / Q000473:pathology*; D008682:Metatarsal Bones / Q000473:pathology*; D010805:Physical Conditioning, Animal / Q000009:adverse effects