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Vet Notes: Palmar/Plantar Osteochondral Disease

on Thursday, 01 May 2014. Posted in Blog

Vet Notes: Palmar/Plantar Osteochondral Disease

Peterson & Smith sends out Vet Notes each month (unless things get  crazy…which they sometimes do!) with our statements for clients. Not a client, but still interested? Don’t have a statement this month? Have no fear! Here are our latest notes, from Kelsey Kunce, DVM, on Palmar/Plantar Osteochondral Disease. Don't forget - we have TONS of vet notes from the past on our website.

 Palmar/Plantar Osteochondral Disease
Kelsey Kunce, DVM

Throughout an animal’s life, cells called osteoclasts and osteoblasts continually reabsorb and rebuild bone. This is the process of bone remodeling. “Stress” is put on bones when muscle pulls against them to achieve motion and as they support body weight in the standing animal. The body detects the amount of stress exerted on each bone and remodels that bone to the best of its ability to match the amount of stress applied to it. Thus, routine exercise results in strong and dense bones.

Horses in training, especially racehorses working at race speeds, exert a tremendous amount of stress on their leg bones, tendons, and ligaments. Palmar/plantar osteochondral disease is proposed to occur when the process of bone remodeling cannot keep up with the amount of stress exerted on the lower portion of the cannon bones. There are studies that demonstrated the area of the cannon bone that is affected has an inherently poorer blood supply than the rest of the lower cannon bone. The blood supply is further reduced when the fetlock is in maximal extension, which occurs during a gallop in horses. The poor blood supply and non-adaptive bone remodeling results in the bone just below the cartilage, known as subchondral bone, to become damaged. The severity of destruction can vary from bruised bone to defects in the subchondral bone resulting in overlying cartilage damage. 

Poor performance is the most common complaint as horses frequently have more than one leg affected. Lameness associated with this disease usually is not consistent or sever enough for a veterinarian to confidently block out, so nuclear scintigraphy is commonly performed for diagnosis. Nuclear scintigraphy involves making a horse radioactive via an intravenous injection, and utilizing specialized cameras to detect the amount of radiation in the tissues. Hydroxyappetite, produced by osteoblasts, has a significant amount of radiation uptake. Therefore, the areas with the most radiation detected signify the areas where bone is being remodeled. As previously mentioned, normal bone remodels continually so all bone takes up some radiation. However, areas of bone that are injured or have increased amounts of stress will have most remodeling and show up as a “hot spot” on the scintigraphy images. 

Palmar/plantar osteochondral disease is diagnosed when hot spots in the lower cannon bones are seen. The mainstay for treating these horses is decreasing the intensity of their exercise at a minimum, although complete rest is usually best. Horses should be rested for at least 60 days and then reevaluated by a veterinarian. One theory is that free choice turnout for these horses is beneficial as it increases the hours per day the horse engages in sub maximal loading and unloading of the bone verses stall rest. If the lameness has resolved after 60 days, the horse can be gradually returned to training. Some studies have suggested jogging horses for 4-6 weeks instead of complete rest and then gradually retuning to full work. A few studies have evaluated performance after diagnosis and treatment of palmar/plantar osteochondral disease, but they have conflicting conclusions.

More research is needed to determine what the prognoses for horses diagnosed with palmar/plantar osteochondral disease, but for now there is not sufficient evidence to show that they are unable to return to racing at an equal or improved racing class. 

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