Subchondral bone microdamage accumulation in distal metacarpus of Thoroughbred racehorses

Abstract

Fatigue damage in the distal metacarpal subchondral bone is common in Thoroughbred racehorses undergoing post-mortem and appears to accumulate throughout a racing career. Reduced intensity or duration of training and racing and/or increased duration of rest periods may limit microdamage accumulation. Focal subchondral bone sclerosis indicates the presence of microdamage.

Investigation of changes in bone density and chemical composition associated with bone marrow oedema-type appearances in magnetic resonance images of the equine forelimb

“…The majority of the BMOA lesions observed in the equine metacarpophalangeal joint occurred at a characteristic location corresponding to the region of greatest loading within the joint, in a region associated with palmar osteochondral disease [29, 30]. The data presented here demonstrated an association between BMOA and locally increased bone density, without an associated change in the chemical composition of bone.…”

“…It is of interest that the majority of the BMOA lesions observed were in a very specific location, corresponding to the region of greatest loading within the joint and which is associated with injury and lameness in racehorses [29, 30]. High levels of training amongst young horses, such as race-horses, have been shown to be associated with micro-fractures at high-strain sites including the dorsal third metacarpal [30] and it does appear likely that the apparently characteristic location of the BMOA is related to the loading upon the joint. This may be linked to traumatic damage in some way, even in the absence of clear damage to the articular cartilage, although there was no evidence of microfracture within the samples studied.…”

Clinical insights: Advances in diagnostic imaging: Fractures

“…Subchondral bone plate thickness at the parasagittal groove measured using MRI was greater in horses with lateral condylar fracture than those without fracture . Micro CT can also demonstrate fatigue damage in the distal metacarpal subchondral bone . However, high‐resolution peripheral quantitative CT did not specifically predict condylar fracture which might relate to lack of a clear distinction between the subchondral plate and the trabecular bone using this modality .…”

Mind the gaps: The science of POD and the racehorse fetlock

“…Some, such as acetylsalicylic acid 17 are prescribed due to hoped‐for actions such as ‘increased blood flow’ to dense subchondral bone, however, any review of scientific literature reveals that the medical plausibility of this use to be tenuous at best. A far stronger rationale exists for rest and rehabilitation to permit time for reparative bone remodelling to occur, as suggested by recent authors 5,6,7 . However, further scientific investigation is also needed here, particularly as clinical experience of even prolonged rest of POD‐affected horses has been mixed.…”

“…To commence with the strongest end of the science of POD, the subchondral bone of the racehorse's distal third metacarpus/metatarsus is now arguably the most intensively researched orthopaedic site in the horse. Post‐mortem studies undertaken in the UK and HK 2‐4 defining the gross articular and subchondral lesions associated with POD have been built upon latterly by prodigious research output investigating the microscopic changes‐ both adaptive and pathologic‐ that occur in the subchondral bone of the racehorse in response to training 5‐7 . Research interest has of course been primarily focused on describing the natural history of condylar fractures (which typically propagate from the parasagittal groove), but in doing so much has also been learned about POD lesions thanks to the anatomical proximity of the predilection sites for these injuries 8 .…”