Metacarpophalangeal joint injury patterns on magnetic resonance imaging: A comparison in racing Standardbreds and Thoroughbreds

The metacarpal condyle has received extensive attention as a predominant site of overload arthropathy in racehorses. However, detailed descriptions of MRI lesion patterns for the metacarpophalangeal joint and comparisons between types of racing horses are currently lacking. Aims of this retrospective, cross-sectional study were to describe and compare standing low-field magnetic resonance findings in the metacarpophalangeal joints for groups of Standardbreds and Thoroughbreds using systematic semiquantitative scores. Data archives at the Clinique Vétérinaire Equine de Chantilly and Imavet were searched during the period from June 2010 to February 2016. Images were retrieved and reviewed by one reader. A total of 30 Standardbreds and 77 Thoroughbreds were sampled. The Thoroughbreds developed a much higher rate of stress fractures (40.3% vs. 10%) and overall more severe scores of subchondral sclerosis and bone marrow lesions than Standardbreds. The Standardbreds had more sites of subchondral bone defect and resorption, as well as higher synovitis and joint capsule thickening scores. Both Standardbreds and Thoroughbreds frequently developed multifocal subchondral lesions not limited to the distal palmar condyle. The Standardbreds had a higher tendency to develop dorsomedial joint pole subchondral injuries. Both Standardbreds and Thoroughbreds developed a noticeably high rate of periarticular soft tissue injuries (36.7% in Standardbreds and 20.8% in Thoroughbreds), which were rarely considered as the main contributors to the lameness. Findings supported the use of low-field MRI as a whole-organ assessment tool for Standardbreds and Thoroughbreds with suspected metacarpophalangeal joint injuries.