MRI for Localized Fetlock Lameness Diagnosis

Your performance horse is lame, and while your veterinarian has narrowed the problem down to the animal's fetlock, no abnormalities are visible on radiographs (X rays). Magnetic resonance imaging (MRI) has long been used as a diagnostic tool for lameness and performance issues in horses, and your vet says that's an option. Could that modality help uncover something in the fetlock that radiographs couldn't? According to one research team, it's entirely possible.

Jennifer King, DVM, a former equine orthopedic sports medicine fellow at the WSU Department of Veterinary Clinical Sciences, and colleagues completed a retrospective study on MRI findings in localized lameness cases. She presented the results at the 2011 American Association of Equine Practitioners convention, held Nov. 18-22 in San Antonio, Texas. (Editor's Note: Learn more about the technology behind MRIs in Review of Available MRI Systems on TheHorse.com.)

"Recently results were compiled from a group of horses (that underwent an MRI procedure either) at Washington State University from 1997 to 2009 or Oakridge Equine Hospital in Edmond, Okla., from 2004 to 2009," King explained.

King et al. reviewed records of 244 horses with lameness localized to the fetlock using clinical signs or local diagnostic anesthesia (nerve blocks). Each horse underwent MRI examination so the clinicians could determine a definitive diagnosis. King also noted each horse's breed and riding discipline.

Key findings included:

  • The most common injuries diagnosed on MRI were oblique distal sesamoidean ligament injuries (31%; the distal sesamoidean ligaments include four ligaments--straight, paired oblique, paired cruciate, and paired short distal sesamoidean ligaments--that comprise the distal suspensory apparatus), bone and cartilage injuries (23%), and straight distal sesamoidean ligament injuries (21%);
  • Straight distal sesamoidean ligament injuries were more commonly diagnosed in Warmbloods than in Quarter Horses or Thoroughbreds, while bone and cartilage injuries were least common in Warmbloods;
  • Fractures and bone and cartilage injuries were more commonly observed in Thoroughbreds than in Quarter Horses or Warmbloods;
  • Deep digital flexor tendon injuries were detected more commonly in Quarter Horses than in Warmbloods or Thoroughbreds;
  • Straight distal sesamoidean ligament injuries were most commonly seen in dressage horses; and
  • Fractures were most commonly seen in Thoroughbred racehorses.

So what does this mean for the horse owner? King stressed that MRI is invaluable for diagnosing leg lamenesses correctly, despite the fact that a number of injuries might appear similar to one another clinically (during lameness exam).

"It is also important to mention that there was a group of horses not included in the study that had abnormalities on radiographs and additional injuries were observed on MRI," she noted, which indicated that in some cases MRI, when used in conjunction with radiographs, can visualize more injuries or abnormalities than radiographs alone.

"The wide variety of abnormalities observed points out the value of MRI for making an accurate diagnosis in performance horses with lameness localized to the fetlock region," she concluded. "A correct diagnosis means that we can offer treatment options that address those issues."

When to Choose MRI

Although MRI might seem like a costly option that could be avoided, King advised owners to consider it sooner rather than later when diagnosing a difficult lameness.

"MRI is currently the best option for imaging bone and soft tissue injuries once the lameness has been localized," she explained. "While some people choose to wait until they are at 'wit's end' to pursue MRI--either because they waited due to financial constraints or the option of MRI was not offered to them--there can be significant disadvantages at this point."

"Horse owners may have spent well over the cost of an MRI (typically around $2,000, depending upon what part of the country the horse resides in, she estimated) on other diagnostic imaging modalities or treatments that were aimed at a diagnosis that was not accurate," King continued. "Furthermore, acute injuries may be chronic at this point, thereby decreasing the effectiveness of treatments and perhaps decreasing the prognosis depending on the injury."

While MRIs were previously limited to a few select facilities throughout the country, King noted there are several traveling MRI units that allow horse owners and veterinarians in most parts of the United States access to this technology.

"If your horse's lameness has been localized to a region and does not have a definitive diagnosis, you should ask your veterinarian about MRI," she concluded. "An accurate diagnosis is the first step in developing a specific treatment plan and getting a horse back into performance."--Erica Larson

Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.