Computed Tomography for Imaging the Stifle

The stifle joint is often implicated in cases of lameness, but it can be a notoriously tough joint to image. Radiography, ultrasonography, nuclear scintigraphy (bone scan), and diagnostic arthrography (joint evaluation) all can be used, but they all have limitations. And no currently available MRI units are big enough to accept a horse's stifle for imaging.

Computed tomography (CT), however, might be able to image the stifle with detail approaching that of MRI, and with a shorter examination time. At the 2007 American Association of Equine Practitioners Convention, held Dec. 1-5 in Orlando, Fla., Erik Bergman, DVM, Dipl. ECAR, a veterinarian from Lingehoeve Diergeneeskunde, in Lienden, the Netherlands, presented a study of the technique and clinical application of stifle CT evaluation.

"Historically, CT has been infrequently used to evaluate the anatomy of the upper limbs for a variety of reasons, such as the physical constraints of the horse, gantry (ring around the imaging tunnel) size, X ray tube output, and difficulties in linking a table strong enough to support a horse to the CT scanner," he noted. "Advances in all of these areas--in addition to CT-scanner software and hardware improvements--have made the technique reported possible."

After development of CT arthrography (joint evaluation) technique via contrast media on cadaver specimens, Bergman described the findings and procedures used to evaluate stifles on 16 horses with CT (general anesthesia is required). Horses were grade 2-4/5 lame on the AAEP lameness scale, and pain had been localized to the stifle joint by joint blocks and thorough lameness examinations.

"CT should be considered complementary to a complete clinical examination and other diagnostic imaging modalities." –Dr. Erik Bergman
Diagnostic images were achieved in all horses, and ultrasound-guided contrast media injection for arthrography was successful in all cases. Lesions were found on CT that correlated with the clinical exam in 14 of the 16 horses, and 12 horses had multiple lesions. The most common problem was a lesion of the meniscotibial ligament and/or its insertion onto the proximal tibia, which was found in six of 16 horses (37.5%).

"CT was vastly superior to radiography for evaluation of hard tissues, including bone and dystrophic soft tissue mineralization," he reported. "Ultrasound and radiography consistently underestimated the extent of bone remodeling in these cases."

Bergman noted that CT arthrography carries two major benefits over radiography and ultrasound--the ability to find lesions not previously seen with these two methods, and a more complete evaluation of the extent of lesions seen with these methods. "In several cases, ultrasound accurately identified the lesions, but the CT scan documented other lesions or more extensive pathology than was suspected."

"In conclusion, the techniques of equine stifle CT and CT arthrography are feasible and clinically useful," Bergman summarized. "CT should be considered complementary to a complete clinical examination and other diagnostic imaging modalities. In this group of clinical cases, CT was useful to define the extent of suspected or previously diagnosed injuries and to identify injuries that were elusive. This information allows clinicians to develop more directed therapeutic plans or provide a more accurate prognosis."

About the Author

Christy M. West

Christy West has a BS in Equine Science from the University of Kentucky, and an MS in Agricultural Journalism from the University of Wisconsin-Madison.

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