Researchers who studied the leg bones of horses found a significant number with abnormal swelling in their bone marrow, with a localised increase in bone density.
The next step is to determine whether these changes are associated with bone micro-damage, which several studies have linked to catastrophic breakdowns in racehorses.
Christine Heales and her colleagues at the University of Exeter in England focused on a condition known as bone marrow oedema-like abnormalities (BMOA).
The cause of these abnormalities, which can be seen on MRIs, are not fully understood.
Excluding those related to trauma, BMOAs in humans are linked with a range of conditions, including nerve damage related to diabetes, osteoarthritis, rheumatoid arthritis and osteomyelitis.
It has also been shown that these abnormalities can arise when sedentary individuals start a running regime. They are generally more common in runners than non-runners. In these cases, it has been suggested that BMOA patterns might represent the early stages of a stress fracture.
For their study, the researchers used magnetic resonance imaging (MRI) to assess 65 limbs from 43 horses collected from an abattoir. Their working histories were unknown, although some indication of age was given by abattoir staff.
The samples obtained were of the distal third metacarpal bone of the forelimb, which is a high-load, high-velocity joint.
BMOAs were found to be present in 19 of the 43 horses.
A subset of 13 limbs provided 25 samples for further investigation, eight of which had BMOA present. Seventeen were used as controls.
The researchers used a technique called projection radiography to assess bone mineral density and Raman spectroscopy to assess bone composition.
They found that BMOA was associated with locally increased bone density, suggesting increased bone formation. However, no measurable changes relating to bone remodelling were found, and there were no detectable changes in the chemical composition of bone.
“It would appear,” they wrote in the journal BMC Musculoskeletal Disrderos, “that the increased bone volume is due to a greater amount of bone being formed rather than an imbalance in relation to bone remodelling.
“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.
“High levels of training amongst young horses, such as racehorses, have been shown to be associated with micro-fractures at high-strain sites including the dorsal third metacarpal 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.”
The authors suggested further work be undertaken work to determine any links between BMOA and micro-fractures, cracks and broader bone remodelling.
“Whilst there are differences between equine and human bone it is also felt that there are similarities, for example in the pathogenesis of osteochondrosis that may also render these findings applicable to the human population.”
The study team comprised Heales, Ian Summers, Jonathan Fulford, Karen Knapp and Peter Winlove.
Investigation of changes in bone density and chemical composition associated with bone marrow oedema-type appearances in magnetic resonance images of the equine forelimb
Christine J. Heales, Ian R. Summers, Jonathan Fulford, Karen M. Knapp and C. Peter Winlove
BMC Musculoskeletal Disorders 2019 20:330 https://doi.org/10.1186/s12891-019-2693-y