Low-Field MRI Useful for Assessing Sesamoidean Ligaments

Researchers found that standing MRI is effective for viewing the difficult-to-image ligaments in the horse’s lower legs.
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Veterinarians have access to a variety of tools for looking inside horses’ bodies, but not every imaging option is ideal for all types of tissue or anatomic location. And it can take a bit of trial and error to determine which modalities are best for viewing particular body parts. For instance, researchers recently tested standing MRI’s efficacy for viewing difficult-to-image ligaments in the horse’s lower legs, and they had very promising results.

Collectively, the distal sesamoidean ligaments (DSL) are a continuation of the suspensory ligament branches and are located behind the pastern, between the fetlock and the hoof. Injuries to these structures pose a serious risk to a horse’s athletic career—they are crucial for the proper function of the entire suspensory apparatus and the stabilization of the lower limb. Oblique distal sesamoidean ligament (ODSL, which attach to the sesamoid bones and their interconnecting ligament and to back of the long pastern) inflammation, or desmitis, typically results from fetlock joint hyperextension.

The ODSLs are located deep under the skin’s surface. Radiographs can help rule out fractures of the associated bony structures, but ultrasound and MRI generally offer a better look at the ligaments themselves. But even those modalities have drawbacks. Because of the natural shape of the horse’s lower leg, it is difficult for veterinarians to maintain good surface contact with an ultrasound probe, resulting in a poor image and an inconclusive diagnosis. High-field MRI provides superior images, but is expensive and requires general anesthesia.

To that end, a team of researchers recently sought to determine whether low-field MRI (standing MRI or sMRI), which requires only mild sedation and costs less for the owner, could be useful for visualizing the DSLs.

Fumiaki Mizobe, DVM, of the racehorse hospital at Japan Racing Association’s Ritto Training Center, and colleagues evaluated three Thoroughbreds with ODSL injuries. Each horse underwent radiographs, an ultrasound exam, and sMRI.

The team determined that radiographs effectively ruled out fractures in the associated bony structures, while changes to the DSLs were only visible on ultrasound when there was significant damage. They found that the images obtained via sMRI, on the other hand, allowed a detailed evaluation of each type of tissue. As such, the team concluded that sMRI is an excellent way to diagnose ODSL desmitis.

The study was limited by the small number of cases, but images acquired via sMRI were determined to be superior for diagnosing ODSL desmitis compared to the other modalities tested, the researchers said.

The study, “Use of standing low-field magnetic resonance imaging to assess oblique distal sesamoidean ligament desmitis in three Thoroughbred racehorses,” will appear in an upcoming issue of the Journal of Veterinary Medical Science

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Written by:

Nettie Liburt, MS, PhD, PAS, is an equine nutritionist based on Long Island, New York. She is a graduate of Rutgers University, where she studied equine exercise physiology and nutrition. Liburt is a member of the Equine Science Society.

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