Through general anesthesia and creative positioning techniques, veterinarians can take advantage of this “otherwise commonplace diagnostic tool” to view the multiple structures inside the stifle—even in large-bodied sport horses. The knowledge gained from such views could contribute to not only better diagnoses and therapies for the patient but also improved general knowledge about the equine stifle within the scientific community, said Sarah M. Puchalski, DVM, Dipl. ACVR, of Puchalski Equine Imaging, in Gibsons, British Columbia, Canada.

“Ingenuity and perseverance by some equine veterinarians and equine diagnostic imaging equipment vendors have shown that the technology is useful and the procedure is possible for most horses, including sport—Olympic and Western disciplines—and racehorse populations,” Puchalski said, presenting at the 2022 British Equine Veterinary Association (BEVA) Congress, held Sept. 7-10, in Liverpool.

Puchalski provided attendees with a slideshow of images, mostly from the Martin Waselau Clinic in Germany, of horses undergoing MRIs of the stifle joint. The horses were fully anesthetized, placed on their backs, and had one hind limb pulled up and extended in order to get the stifle joint within the unit’s viewing range.

“The person on top of the gantry unit (will) tie the foot into that extended position to get the center of the stifle into the sweet spot of the magnet, which is a challenge,” she said.

In clinical practice MRI imaging of the stifle has uncovered  injuries to individual soft and hard tissues, as well as to multiple structures, she said. In particular, she and her fellow researchers have detected injuries in the cruciate ligaments, the menisci and its associated ligaments, the collateral and patellar ligaments, and the femoral and tibial condyles and patellae.

Horses with such injuries usually have varying degrees of lameness, Puchalski said. But cadaver studies have revealed that in some cases, horses have visible lesions on MRI but were asymptomatic prior to euthanasia.

MRI is the current “go-to” for diagnosing disease in bones and soft tissues, said Puchalski. But it’s still not a perfect imaging tool. Among other disadvantages, it doesn’t provide reliable viewing of cartilage, she explained. And MRI images can have various artifacts—a sort of image pollution usually related to the way the image is captured—that can skew results.

Its other major drawback—and the “elephant in the room” with regard to MRI imaging of the equine stifle—are the risks related to general anesthesia, which is necessary due to the complex positioning. “They haven’t been reported, but I know anecdotally that there have been some, particularly in the beginning with the positioning and the long anesthetic protocols,” she said.

In general, there’s very little information in scientific publications about MRIs of horse stifles, said Puchalski. To compensate for that lack, she encouraged veterinarians to share their knowledge, clinical experiences, and findings to improve the practice and interpretation of images.