Changes in mineralised tissue at the site of origin of condylar fracture are present before athletic training in Thoroughbred horses

Abstract

AIM: To show that changes are present at the site of origin of metacarpal condylar fracture in young Thoroughbred horses before they enter race training.

METHOD: Bone slices, 2 mm thick, in three mediolateral planes through the centre of rotation of the metacarpo-phalangeal joint (MCPJ) of both distal third metacarpal bones (Mc3) of 12 Thoroughbred horses aged 17 months, were imaged using point-projection digital X-ray imaging (µXR).

RESULTS: In some horses, linear or ovoid radiolucency was found in articular calcified cartilage (ACC) and subchondral bone of the palmaro-distal aspect of the sagittal groove, exactly at the site of more advanced stages of condylar fatigue fracture. An incidental finding was ovoid radiolucency in the apex of the dorso-distal aspect of the sagittal ridge, with or without fragmentation or disturbance of the subchondral mineralised tissue line, resembling equine osteochondrosis.

CONCLUSIONS AND CLINICAL RELEVANCE: The findings imply that the aetiology of condylar fatigue fracture in young Thoroughbred horses includes abnormality in development of the bone and joint that is present before athletic activity occurs.

KEY WORDS:

• Condyle
• fatigue fracture
• calcified cartilage
• subchondral bone
• equine
• bone development
• osteochondrosis

Acknowledgements

The study was supported financially by a Horserace Betting Levy Board veterinary project and a veterinary research training scholarship, and by the New Zealand Racing Board. We thank Dr Tertius Hough (Medical Research Council, Harwell, UK) for use of the Faxitron imaging system, and Maureen Arora for technical assistance. We thank the Global Equine Research Alliance for access to tissue, and Marilyn Simpson Trust (USA), Horserace Betting Levy Board (UK), Utrecht University (The Netherlands), and the New Zealand Racing Board for funding toward the clinical study.