Imaging Explained explores the different modalities available to help with lameness diagnosis, and what you can expect from each. Here we take a deep dive into ultrasound.
What is ultrasound?
Ultrasonography – or ultrasound – is the complementary tool, widely used to assess soft tissue structures such as tendons and ligaments. Like radiography (X-ray), it is portable and generally affordable. However, sound waves cannot easily pass through bone or air, limiting its view to structures adjacent to the bone surface. Ultrasound also allows dynamic assessment of soft tissues when needed.
When might we use ultrasound?
- Assessment of areas of swelling to determine underlying soft tissue involvement
- Investigation of soft tissue injury (tendons, ligaments)
- Evaluation of synovial structures (tendon sheaths, bursae, joints) for effusion or pathology
- Guidance for diagnostic or therapeutic procedures (e.g. injections)
- Monitoring healing during rehabilitation
What it shows well
- Fibre pattern, size and echogenicity (tissue brightness) of tendons and ligaments e.g. assessing a core lesion
- Oedema and swelling of the subcutaneous tissues
- Bone surface irregularities
- Foreign bodies in soft tissues
- Synovial structures: joints, tendon sheaths, and bursa
What it doesn’t show well
- Deep structures hidden by bone or air
- Internal hoof soft tissues due to the difficulty of imaging through the hoof itself
What to expect from ultrasound
Your vet will clean and/or clip the area in question and apply gel to get the best image possible (air between hair prevents ultrasound from working). Most horses are scanned whist standing and mild sedation is used, if needed, for accuracy and safety. Serial scans to monitor progress can help track healing.
Where it fits into the bigger picture
If ultrasound and X‑rays don’t answer the question (or if the issue is inside the hoof capsule or complex joint), your vet may suggest moving on to CT for intricate bone architecture or MRI which excels at imaging soft tissue. To learn more about how ultrasound compares to MRI, check out this article written by Ellen Law. Ellen works as a radiologist at the Diagnostic Imaging Unit of the Swedish University of Agricultural Sciences, University Animal Hospital.
