Using MRI and Scintigraphy to Diagnose Suspensory Injuries (AAEP 2012)

The biblical saying, "two are better than one because they have a good return for their work," succinctly describes recommendations Natalie Zdimal, DVM, recently made regarding diagnostic imaging for suspensory-ligament-related injuries. Horses with such injuries generally have discomfort in the back the back of the fore- and hind-limbs near the knee and hock joints.

"Injuries in those areas are a common source of lameness in equine athletes," said Zdimal, currently a practitioner at Bayhill Equine Sports Medicine & General Practice, in Redwood City, Calif., during the 2012 American Association of Equine Practitioners' Convention, held Dec 1-5 in Anaheim, Calif.

She added that with these particular horses, "injury to the (suspensory) ligament has been the primary focus historically, but we now know that ... the ligament, the bone-ligament interface, and the bone surface can all sustain injury and cause lameness."

Veterinarians can use several diagnostic tools to determine the cause of such lameness, but they haven't yet proven one method superior. This is likely because proximal suspensory apparatus injury or pathology (damage) is complex. Nuclear scintigraphy (bone scans) and magnetic resonance imaging (MRI) are two options for diagnosing lameness and, particularly, injuries that occur in the proximal suspensory apparatus area.

Immediately before performing a bone scan, veterinarians inject a horse with a radioactive compound (usually Technecium-99m) that accumulates at the site of injury. During the bone scan, practitioners look for "hot spots," or areas of increased uptake of the compound. To determine if these hot spots correlated with specific pathology identified on MRI, Zdimal and colleagues at Alamo Pintado Equine Medical Center, in Los Olivos, Calif. (where she recently completed an internship), reviewed the medical records of 26 horses evaluated for pain in the back of the limb, near the knee or hock.

The team found that:

  • Nuclear scintigraphy can help practitioners identify regions of anatomic abnormalities (hot spots);
  • No statistically significant correlations existed between hot spots and specific abnormalities on MRI;
  • Horses with mild hot spots were more likely have injuries to the suspensory ligament alone, whereas horses with more intense hot spots were likely to have a combination of both bony and ligamentous injury; and
  • MRI was useful for diagnosing injury to the suspensory ligament near its origin at the top (proximal aspect) of the cannon bone, near the knee and hock joints.

Zdimal concluded, "Together these findings suggest that nuclear scintigraphy is effective at localizing regions of bone pathology and is an important component of the diagnostic workup, as all horses evaluated had pathologic lesions found on MRI. But additional diagnostics are required when making a definitive diagnosis. Scintigraphic findings were shown to be nonspecific and less sensitive at identifying soft tissue injuries in equine orthopedic conditions when compared to MRI."

In other words, veterinarians can use a bone scan to identify the region of the limb that is causing the lameness/pain, and with MRI, they are better able to determine the specific cause.

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