Radiology is the oldest diagnostic imaging technique (over a century old), providing an excellent morphological representation of horse bones. It is currently the technique with the best diagnostic image definition. It is particularly useful for diagnosing established bone and joint lesions in horses.
X-raying a horse
The principle behind X-ray imaging is to expose a sensitive film through a screen that emits light when irradiated with X-rays. The technique therefore requires an X-ray generator and cassettes containing a film applied against one or two screens. After exposure, the film is developed using a developer bath, then fixed and rinsed. The more X-rays the film receives, the darker it emerges from development. X-rays penetrate air very easily, so the lungs and trachea are radiolucent and appear dark on the image. Bone, on the other hand, because of its calcium content, stops X-rays; as a result, limb bones and vertebrae appear radio-opaque, i.e., white on the X-ray image. The “soft tissues” – muscles, ligaments, tendons, articular cartilage, and synovial fluid – all have the same radiographic density (due to their water content) and appear grey on the X-ray. X-rays are therefore difficult to differentiate. Some veterinary centers or clinics have a radiology room equipped with a powerful X-ray generator, enabling examination of all areas of the horse’s body. Specialized examinations such as those of the back (fig. 1) or shoulder, particularly indicated for competition horses, can thus be carried out.
In some veterinary clinics, horses are now examined using digitized radiography: the image recorded on the screen is directly analyzed by a digitizer and transmitted to a computer, where it can be reworked using various functions (blackening modification, detail enhancement, etc.). This process enables the image to be modified a posteriori to enhance the visualization of certain demineralization lesions, for example. It is also possible to compose images presenting a horse’s complete radiographic check-up, and to duplicate them at will – a considerable advantage for communication between vets and horse owners.
Indications for X-raying your horse
The indications for X-ray examinations of horses vary widely, from medical pathology (e.g., lungs and head) to surgery (e.g., checking osteosynthesis techniques). However, the main reasons for using X-rays are to diagnose lameness and to examine the limbs during purchase visits.
Once the site of lameness has been identified (foot, hock, etc.), radiology is an irreplaceable means of identifying and documenting osteoarticular lesions. This technique makes it possible to identify juvenile osteoarticular affections from the foal’s earliest years (often before weaning). In the case of trauma or recent lameness, it is indispensable in the search for and identification of fractures. In horses with chronic lameness, radiography is also the best technique for diagnosing degenerative osteoarticular lesions that appear over the years. It remains the basic technique for diagnosing arthropathies, thanks to its specificity in cases of alteration of the subchondral bone and periarticular osteophytes.
Technological advances have made it possible to examine all areas of the horse, particularly the back. This examination is of great interest to athletic horses, whose back pain is one of the main causes of reduced performance.
Benefits and limitations of radiology in horses
The benefits of radiography are numerous. In the field, at the patient’s bedside, it is easy to implement in everyday practice. The cost/information ratio is good.
However, radiography also has its limitations:
- low sensitivity to moderate bone demineralization;
- low sensitivity to early or established cartilage lesions;
- its lack of sensitivity to capsular, ligament and synovial lesions, except in the case of mineralization or pull-out fractures.
That’s why this indispensable technique is now used in conjunction with other procedures, such as ultrasound, to overcome these limitations.
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To find out more: radiological assessment of the horse
