Ultrasonography (ultrasound scanning) is a safe, very useful and non-invasive technique used primarily for assessing "soft tissue" structures. If the findings of our lameness exam indicate there could be a problem with the tendons, ligaments or muscles usually an ultrasound exam is the next step we would recommend.
How does ultrasound work?
Ultrasound is safe, painless, and produces pictures of the inside of the body using sound waves. Ultrasound imaging involves the use of a small transducer (probe) and ultrasound gel placed directly on the skin. High-frequency sound waves are transmitted from the probe through the gel into the body. Ultrasound waves travel through and "echo" back to the transducer from different tissue densities. The transducer collects the waves that bounce back and a computer then uses those sound waves to create a picture giving detailed real-time images of a wide range of anatomical structures. Bone, which is dense, is identified on screen as a bright white line, whereas a tendon appears as shades of grey and fluid is black. Although ultrasound cannot be used to examine the deeper structures in bone as bone matter is too dense it can be used to investigate problems of bones in areas where obtaining good quality x-rays is problematic, such as the pelvis and spine. We can also use it to assess bone margins and to look at the attachment of soft tissues to bone or changes on the surface of the bone. Ultrasound does not use ionizing radiation (as used in x-rays), so there is no radiation exposure to the operator or patient. Because ultrasound images are captured in real-time, they can show the structure, function and movement of the area we are imaging, as well as blood flowing through blood vessels.
How do we perform an ultrasound examination?
When you bring your horse in for an ultrasound, unless the problem is glaringly obvious (like a bowed tendon), we prefer to evaluate the horse clinically first. This is important as we need to be able to adequately interpret the images in context with how the horse is clinically.
We may need to clip the hair of your horse to obtain good ultrasonographic images (the hair interferes with image quality). Please let us know if this is an issue for you at the time of the consultation. Your horse may also require a mild sedative to make the procedure as safe as possible and allow us to obtain the best quality images.
If we are doing a scan of the lower limb we may sit down and get comfortable! Imaging the lower limbs requires good contact between the probe and the curve of the leg so we have to press quite firmly and we may use a “standoff”(a flexible cover over the end of the probe allowing for better contact and imaging of the area in cross section)
Depending on the area we are assessing the ultrasound examination may take around 30 minutes. We will scan, record, label and store images and video clips of the area which if necessary, will allow for serial assessment as the horse undergoes treatment and rehabilitation. We can use still images to measure the size of lesions as a cross-sectional area, this allows accurate follow-up of the size and healing of lesions. We may also assess the opposite side or normal limb to provide a direct comparison to the problem area.
With lower limb tendon and ligament injuries ultrasound examination is most helpful in the first 1-2 weeks following injury. We ideally like to reassess these limbs a few weeks later to gauge healing following treatment and rest, and then again following a rehab programme before the horse is returned to full work (approximately 6-12 months after initial injury).
What orthopaedic conditions and areas can be assessed with ultrasound?
Lower limb: Commonly we would assess the deep and superficial flexor tendon, the flexor tendon sheath and the suspensory ligament and its medial and lateral branches. Ultrasound is used routinely to assess these structures for injury and to monitor ongoing response to treatment.
Upper limb: Ultrasound may be used in the upper limb to assess areas of muscle damage or any other injuries. In areas that are deep and difficult to radiograph like the hip joint it can be used to provide us with information about the immediate bone and ligamentous structures around the joint.
Joints: Commonly we may use ultrasound when assessing for joint infection and inflammation as well as general joint health. We can also examine the collateral ligaments which stabilise the joint for damage and we can use ultrasound in some cases to help us visualise the structures inside the joint such as the cruciate ligaments and meniscus of the stifle joint.
Foot: Although is it not done as commonly as x-ray or MRI, ultrasonography of the foot can provide information on many of the soft tissue structures that cannot be seen on x-ray including the deep digital flexor tendon and the navicular bursa.
Neck: Horses with neck pain can exhibit a range of symptoms from low grade forelimb lameness to obvious neurologic symptoms. We can ultrasound these important joints and identify any inflammation or bone changes that may be contributing to nerve compression resulting in pain.
Back: It can be difficult to x-ray the deeper structures of the back; we can therefore use our ultrasound to provide information on the joints as well as evaluate for the presence of kissing spines and assess the ligaments and muscle in this region. Imaging in this area may be indicated in horses exhibiting back pain and stiffness.
Pelvis (internal & external scans): we can directly image the sacroiliac & lumbosacral joints of the pelvis via a rectal scan in those horses with lumbosacral pain. More commonly ultrasonography of the pelvis can be helpful when assessing for fractures as the area is difficult to radiograph.
Other uses: Frequently we use ultrasound to help us sample or medicate a specific area with ultrasound guided injections of various bursa, sheaths and joints or to provide treatment such as stem cells directly into a lesion within a tendon or ligament. It is also used to help assess deep wounds and find and remove foreign bodies or fragments of bone or to locate and drain abscesses or haematomas.