Looking only at the X-rays, without taking into consideration other factors, can be misleading. The changes that prepurchase radiographs show have to be looked at in context, taking into account the age of the horse, athletic discipline, how long and how intensively he has been ridden, his conformation, physical examination findings and the results of the lameness examination (both in-hand and under saddle, if possible). Evaluating prepurchase radiographs with this information in mind is essential if the veterinarian expects to offer his opinion on any changes or abnormalities and adequately counsel the buyer about their impact on future soundness. Certain radiographic changes in a horse who already has been doing high-level dressage by age 8 or 9 might mean less than when seen in a 5- or 6-year-old who hasn’t done anything.
A problem often found in radiographs is osteochondritis dissecans (OCD), the failure of bone to fully ossify. This allows for separate fragments to form and become detached from the parent bone. In those cases in which the OCD fragment is big enough or might be limiting the soundness of the horse, they can be removed surgically using arthroscopy (or keyhole surgery), typically carrying a good prognosis.
The most common location for OCD fragments in the horse is off the distal intermediate ridge of the tibia within the upper hock joint, also known as the tarsocrural or tibiotarsal joint. OCD in this area can be considered an incidental finding or “inactive,” another example of why the radiographs have to be evaluated together with the rest of the prepurchase examination.
OCD lesions can remain inactive for the entire life of the horse. Some of these can be difficult to predict, which also makes the discussion the veterinarian has with the potential buyer very important. An “active” OCD lesion in this area can be readily removed arthroscopically. In active cases, the joint will show a variable amount of joint effusion or bogginess, with no real evidence of lameness early on. The outlook in terms of future soundness and athletic ability is typically very good and might not cause a horse to not reach his full athletic potential.
Prepurchase examinations routinely include only radiographs as the main mode of imaging. Although we have made huge progress with the quality of the radiographs taken nowadays, there are some inherent limitations, including identifying cartilage and soft tissue abnormalities.
To make a more objective assessment of the skeleton and certain soft tissue areas, some veterinarians are offering ultrasound and other more advanced imaging modalities, such as magnetic resonance imaging (MRI), computed tomography (CT) and nuclear scintigraphy (bone scans), as part of prepurchase examinations.
So, in other words, if the radiographs are clean, it doesn’t necessarily mean that the horse has no abnormalities or is “clean.”
José M. García-López, VMD, is an associate professor of large animal surgery at Tufts University Cummings School of Veterinary Medicine in North Grafton, Massachusetts.