Radiographs are the technical name for X-rays. They are used to examine the anatomy of the internal structures of horses, either for diagnosis of a disease or before purchasing a horse to confirm that it is sound.
Most equine practices have a portable X-ray machine that can be used for examining the horse in the stable. If better quality images are needed, the horse should be referred to a specialist practice.
On a radiograph, hard tissues, such as bones, that stop X-rays passing through, are seen as white. Soft tissues that allow X-rays to pass through are black. A radiographic image is a two-dimensional representation of a three-dimensional object. In an X-ray machine, radiographs are made by passing an electrical current through a special type of vacuum tube that generates X-rays.
The tube current, which determines the strength of the rays, is measured in milliamperes (mA); the voltage, which measures the number of rays produced, is measured in kilovolts (kV). The third factor is exposure time. These three elements determine whether the radiograph is under- or over-exposed.
Many modern X-ray machines are automatically calibrated. The vet simply enters body part and thickness, and the machine automatically sets the technique (mA, Kv and exposure time) required. Older machines generated radiographs that had to be developed in a darkroom. New machines generate digital images displayed on a computer.
Because X-rays pose a health risk to humans and animals, it is important that the horse is correctly restrained so that there is no ‘scatter’. Proper positioning is also essential to prevent misdiagnosis. This may require sedation or even full anaesthesia.
Radiographs for pre-purchase examinations
One of the main reasons for radiography is the pre-purchase examination of a sport horse, to check whether there are any problems that could result in lameness. A routine pre-purchase ‘protocol’ includes three sets of X-rays of the foot and navicular bone for each leg (12 images); front to back and side views of each fetlock (8 images); front to back, side views and two oblique views of each hock (8 images).
In addition, radiographs of the stifle joints are advised in young horses. Including the consultation fee and sedation, this becomes a fairly expensive exercise, but it is justified if you are paying more than R50 000 for a sport horse to be used for dressage, jumping or reining.
Radiography is not an exact science. Interpretation of images is based not only on the anatomical abnormalities seen on images, but also the clinical examination and history of the horse. False positives are not unknown and horses with ‘ugly’ X-rays have sometimes remained sound for decades afterwards.
An experienced equine practitioner should always be used for pre-purchase radiography. It is also very important to make sure that the horse being examined is the same horse you are purchasing. Use your own vet, rather than the seller’s vet, to do the X-rays.