Study Shows Rest May Increase Odds Of Breakdown In At-Risk Racehorses

Joint surface collapse in horses is a degenerative condition that can result from stress fractures (also called bone fatigue) that accumulate from repeated loading of the legs. While many trainers rest horses suffering from bone fatigue, no exercise may not be the answer—in fact, it can even exacerbate the chance of catastrophic breakdown, reports HorseTalk.

Researchers at the University of Melbourne studied joint surface collapse in horses with palmar osteochondral disease, which affects the lower leg bones. The study sought to see if bone resorption could be correlated with reduced physical activity and contributed to surface collapse in horses affected with the disease, they reported in the Equine Veterinary Journal.

The team used metacarpal bones from 36 deceased Thoroughbred racehorses, 29 of which were in training at the time of their death. The horses had raced anywhere from 0 races to 60 races each. The bones were examined to see what proportion of the joint surface had collapsed using a high-resolution CT scanner. The bones were then placed on a scanning electron microscope to quantify porosity and eroded bone surface.

In 21 of the bones examined, inward collapse of the calcified cartilage layer was observed with the microscope scans. In six cases, no microscope was needed—the damage could be seen with the naked eye.

Where microfractures were present in the calcified cartilage and on the subchondral bone, more joint surface collapse could be seen. Horses that had lower porosity in their deeper bone had greater levels of joint collapse, but there was no correlation between surface collapse and porosity on the bone surface.

Horses that were resting had higher porosity and surface erosion of the bone; in some resting horses, there was an apparent loss of support for the calcified cartilage layer. The researchers noted that collapse of joint surfaces was common in cases of palmar osteochondral disease and likely resulted from stress fractures, which is a known factor in catastrophic racing injuries.

Subchondral bone resorption was correlated to the collapse of the calcified cartilage, which appeared to increase with a limited exercise program. Superficial bone loss was pronounced in horses that had limited exercise, which suggests that the area is prone to degradation of mechanical properties.

While it may seem logical to rest a horse that has stress fractures, the research has shown that this can potentially hasten subchondral bone loss in horses that suffer from palmar osteochondral disease. This research will have implications on the management of subchondral bone injuries in horses, suggesting that a limited workload, as opposed to complete rest, may be the better option.

Read more at HorseTalk.


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