Page 174 - The Veterinary Care of the Horse

lightly sedated for the procedure as restless, nervous horses could easily injure themselves or

damage the equipment. Sedation may be required for accurate positioning of the patient and
VetBooks.ir the X-ray plate, particularly if high exposures are being used.

Summary

Radiography is used as an aid to diagnosis and it may also be useful for giving a prognosis. It
has a value in ruling out the possibility of bony injury in cases with severe soft tissue injury.

However, it does not provide all the answers. A horse may be lame for some time before any
changes are visible on the radiographs. A 40% change in bone density must occur before it
can be seen on the X-ray. Any radiographic changes have to be assessed with care as they

may be due to an old injury and not be the cause of the current lameness. Thus a combination
of thorough clinical examination and experience in interpreting the images is essential.

ULTRASONOGRAPHY

What is diagnostic ultrasound?

Ultrasound machines produce high frequency sound waves. A hand-held transducer (the

probe) is placed against the tissue being examined and the sound waves pass through the
tissues until they meet another tissue of different density. At the interface between two
tissues, the waves are reflected back and used to create an image on the screen. The reflected

sound waves are known as ‘echoes’ and tissues that reflect sound are described as
‘echogenic’. Bone is highly reflective and appears as a bright white line on the screen. If the

sound waves pass readily through less dense tissues and there is little reflection, these appear
as black (anechoic) areas on the screen. The soft tissues of the body have a characteristic

appearance with many shades of grey between the extremes of black and white at each end of
the scale.

Ultrasound first became popular in the 1980s for scanning the reproductive tracts of
mares and this was quickly followed by its use for examination of tendons and ligaments.

Today, ultrasound is widely used for examination of most parts of the body. Essentially,
radiography looks at bones and ultrasound at soft tissues, but the two techniques overlap.

(Figure 5.2.)