A diagnostic pathologist’s guide to carpal disease in racehorses

Abstract

As a pathologist, postmortem examination of the equine carpus can be daunting. The anatomy is complex and oftentimes, small or subtle lesions have significant impact on lameness and secondary lesions such as catastrophic musculoskeletal fractures and other injuries. In performance horses, particularly racehorses, the carpus is a common site of injury and source of lameness. Given the predisposition of racehorses to developing carpal disease, familiarity with clinically relevant anatomy and common developmental, degenerative, traumatic, and inflammatory processes are imperative for thorough postmortem examination. Our aim is (1) to provide a concise summary of clinically relevant anatomy and function that serves as a guide for postmortem evaluation of the equine carpus, and (2) to review common carpal injuries and diseases in actively training, racing, or retired racehorses, including developmental lesions (incomplete ossification, osteochondromata), infectious and inflammatory lesions (septic arthritis and tenosynovitis), and degenerative and traumatic lesions (degenerative and traumatic osteoarthritis, osteochondral fragmentation, and polyostotic catastrophic "breakdown" fractures). Representative gross and histologic images are presented along with corresponding antemortem and postmortem diagnostic images, and a review of current scientific literature pertaining to the pathogenesis of these equine carpal lesions.

Biglycan neo-epitope (BGN262), a novel biomarker for screening early changes in equine osteoarthritic subchondral bone

“…In this study, we examined the middle carpal joints. SCB sclerosis of the third carpal bone (C3) is seen in racehorses, often in combination with clinical lameness, with a higher grade of J o u r n a l P r e -p r o o f sclerosis more likely to be present in lame horses 35,36 . Furthermore, the OA lesions of the carpal bones can lead to micro-fractures, with subsequent intra-articular fractures, which can result in catastrophic injuries [37][38][39][40] .…”

Three-Dimensional Imaging and Histopathological Features of Third Metacarpal/Tarsal Parasagittal Groove and Proximal Phalanx Sagittal Groove Fissures in Thoroughbred Horses

“…Microscopic findings of microcracks in the calcified cartilage and subchondral bone plate, characterised by a single to multiple oblique, linear or coalescing defects extending from the calcified cartilage into subchondral bone plate, were considered as fissures. These histological findings were considered the gold standard for verifying CT and MR imaging identification of fissures [ 6 , 26 , 27 ].…”

Fractures in Thoroughbred racing and the potential for pre‐race identification of horses at risk

“…These foci which are the result of fatigue damage of the bone matrix, act as stress risers that can compromise the mechanical integrity of the whole bone. 67,68 A strong body of evidence indicates that such lesions are part of the pathophysiological pathway to most common fractures that occur in racehorses, including sagittal fractures of the proximal phalanx, 69,70 parasagittal fractures of the distal condyles of the third metacarpal and metatarsal bones, 71 transverse fractures of the distal metaphysis of the third metacarpal bone, 72 complete diaphyseal fractures of the third metacarpal bone, 73 transverse fractures of the proximal sesamoid bones, [74][75][76] slab fractures of the third carpal bone, 77 and stress fractures of the humerus, 67,68 scapula, 78,79 tibia, 80 ilium and lumbar vertebrae. 81…”