How MRI Helps Manage Hock, Suspensory Ligament Injuries

Hock and suspensory ligament problems are common in performance horses, but have variable presentations that can make them challenging to diagnose accurately with traditional imaging modalities. MRI can be helpful for assessing such cases.

Photo: Stephanie L. Church, Editor-in-Chief

When it comes to diagnosing injured horses, imaging can be a veterinarian’s right-hand man. These tools allow the practitioner to see under your horse’s skin to help diagnose injuries, select appropriate treatments, monitor healing progress, and determine prognosis.

This even holds true for injuries to the proximal metatarsal and tarsal region, which includes the hock joints and the surrounding bony and soft-tissue structures (proximal suspensory ligament). Problems in this area are common in performance horses and have variable presentations that can make them challenging to diagnose accurately with traditional imaging modalities (X rays and ultrasound), said Matt Brokken, DVM, Dipl. ACVS, ACVSMR, a clinical assistant professor at The Ohio State University College of Veterinary Medicine, in Columbus. At the 2016 American Association of Equine Practitioners Convention, held Dec. 3-7 in Orlando, Florida, Brokken reviewed how he uses MRI to help take some of the mystery out of diagnosing and treating such injuries.

Magnetic resonance imaging uses magnetic fields to create cross-sectional and three-dimensional images of both bony and soft tissue structures, allowing the veterinarian to clearly visualize multiple tissue types at once. Veterinarians might recommend it after performing a thorough lameness examination and localizing the issue to the proximal suspensory or lower tarsal region (using diagnostic analgesia), but when radiography and ultrasonography are inconclusive, Brokken said.

Veterinarians can use MRI to assess internal structures’ shape (to check for fractures or tears) and size (i.e., inflammation or atrophy), as well as signal intensity (which can indicate edema or fluid collecting in bones or soft tissue). Brokken recommended, when possible, performing MR examinations on the affected limb as well as the contralateral limb for comparison (for subtle changes), as well as to check for bilateral (on both sides) disease.

Case Presentations

We know MRI can help diagnose these challenging cases. Great! Send them to the clinic for examination. But therein lies one of the challenges: What does a horse with proximal suspensory/tarsal lameness—one that might benefit from a MRI exam—look like? It varies, Brokken said.

Most horses will be positive or very positive on flexion tests of the affected area, he said. Some will also be positive to lower-limb flexion.

Some affected horses will have a history of a chronic low-grade lameness, Brokken said. The horse might “warm out of it,” and the lameness might improve with lower hock joint injections. In these horses the lameness is commonly bilateral.

Other horses, however, might have a low-grade lameness that suddenly becomes more severe. In addition, some horses might develop acute moderate-to-marked lameness, though Brokken said this is less common in the hind limbs than in the forelimbs (specifically focusing on the proximal suspensory).

Many horses, he added, have no signs of heat, swelling, or pain in the affected area, aside from lameness. This highlights one of the major difficulties in diagnosing a problem in this area: minimal localizing clinical signs.

Diagnoses

You’ve decided that, based on the clinical signs and the lack of evidence or equivocal results of traditional imaging modalities, an MRI examination is a logical next step in the diagnostic process. What might your veterinarian find?

Proximal (upper) suspensory ligament injuries “There are several types of injuries to the proximal suspensory ligament that have been identified with MRI,” Brokken said.

Common findings on MRI include:

  • Increased ligament size with areas of increased signal intensity, indicative of edema or fiber disruptions. These are often located at or just below the suspensory’s attachment to the proximal cannon bone. Brokken said he’s also identified increased signal in horses with injury to the suspensory extension, which connects to one of the tarsal bones and spans the lower hock joints.
  • Brokken has also identified irregular and thickened tissue near the lateral splint bone. “At surgery,” he said, “these horses have adhesion or increased tissue formation that extends from the ligament to the splint bone.”
  • Some horses develop abnormalities at the back of the cannon bone, where the suspensory ligament attaches (top of cannon bone), he said. In some horses, the injury to the bone is the primary abnormality instead of the ligament.

Hock abnormalities Brokken said MRI has allowed veterinarians to visualize damage to the articular surfaces of the upper and lower hock joints. “In particular, MRI has allowed us to identify horses with lower hock cartilage/bone damage associated with the joints, as well as the bones surrounding the intertarsal ligaments,” he said.

Other abnormalities Although less common than hock or suspensory injuries, Brokken said other diagnoses, including flexor tendon injury at the level of the proximal suspensory or hock, could cause lameness.

Treatment

You’ve reached a diagnosis. Excellent! Next, your veterinarian will prescribe a treatment. Brokken said MRI exams can help practitioners choose targeted treatments that will give the horse the best chance to return to function.

Veterinarians can attempt to treat soft-tissue injuries (i.e., high suspensory) using conservative therapy, although, he noted, the success rates are lower in hind limbs than forelimbs for treatment based on rest and controlled exercise. Surgical options, which are more successful, can include neurectomy (removing a piece of the nerve that innervates, or supplies, the suspensory ligament and, thus, causes pain in chronically enlarged suspensory ligaments) and/or fasciotomy (cutting the fascia to relieve pressure on the enlarged ligament), among other procedures.

Tarsal injury treatment depends on the nature of what the veterinarian finds on MRI. If there’s bone but no joint involvement, treatment might only consist of rest to allow the bone to remodel, he said. If there’s damage in the hock joints, veterinarians will likely either opt for corticosteroid injections, with or without hyaluronic acid, or a surgical procedure called arthrodesis (fusing low-motion joints, such as the lower hocks).

Throughout the course of treatment, follow-up MRIs can shed light on the healing progress, as well as the likelihood that the horse will return to work.

Take-Home Message

“MRI is a valuable diagnostic modality that allows diagnosis in horses with lameness localized to the proximal metatarsal and tarsal regions,” Brokken concluded. “The ability to accurately diagnose the source of lameness is important in selecting treatment that will maximize the chance to return to performance.”

About the Author

Erica Larson, News Editor

Erica Larson, news editor, holds a degree in journalism with an external specialty in equine science from Michigan State University in East Lansing. A Massachusetts native, she grew up in the saddle and has dabbled in a variety of disciplines including foxhunting, saddle seat, and mounted games. Currently, Erica competes in eventing with her OTTB, Dorado.

Stay on top of the most recent Horse Health news with FREE weekly newsletters from TheHorse.com. Learn More