Ultrasound of the Collateral Ligaments of the Equine Tarsus
by Suzan C. Oakley, DVM, Diplomate ABVP(Equine)
Tarsal collateral ligament injuries are not uncommon and should be considered when evaluating hock pain or swelling. Desmitis and enthesitis (injury at the site of attachment to the bone) of the collateral ligaments or avulsion fractures at sites of origin or insertion can occur.Severe injuries to the collateral ligaments are often caused by trauma, but mild or subclinical injuries could contribute to hock pain and/or distal tarsal joint degenerative joint disease (DJD) due to a lack of medial to lateral stability. It has been reported that injury to the medial collateral ligament resulted in DJD of the distal tarsal joints secondary to instability.
The collateral ligaments are easy to palpate and identify with ultrasound. Injuries to these ligaments, as with other ligaments in the body, are characterized by enlargement, hypoechoic areas and disruption of fiber pattern. Calcification within the ligaments may also be present and identified with ultrasound. The anatomy and normal ultrasonographic appearance of the medial and lateral collateral ligaments of the hock will be reviewed here. There are several excellent references which provide a comprehensive review of the anatomy and ultrasonography of the tarsus.