CT Scans Can Help Diagnose Stifle Lameness

In sport horses, stifle lameness is an important cause of loss of use. But diagnosing problems in this hind limb joint is no easy task due to its location and complexity.

Some veterinarians and researchers have proposed using computed tomography arthrography (joint evaluation) to evaluate the stifle joint. So Sarah Puchalski, DVM, Dipl. ACVR, associate professor of surgical and radiological sciences at the University of California, Davis, School of Veterinary Medicine, traveled to the Netherlands to study this technique. She shared her findings at the 2013 American Association of Equine Practitioners convention, held Dec. 7-11 in Nashville, Tenn.

"(The stifle's) multiple intercapsular soft tissue structures are complex," Puchalski began. "If any of them are injured, it can cause lameness."

Diagnosing stifle lamenesses typically requires anesthesia and an imaging technique such as radiography, ultrasound, or nuclear scintigraphy. However, none of these methods are without flaw.

"Radiographs are insensitive, ultrasound is very useful but limited to certain portions of the body, and scintigraphy can be useful but is also very insensitive," Puchalski explained.

Computed tomography (CT) is an imaging method that uses X rays to produce cross-section images of the body. Scanning large body parts on horses can be difficult, and a special CT table design is required to evaluate an equine stifle. Lingehoeve Diergeneeskunde, a veterinary clinic in Lienden, the Netherlands, however, owns a CT scanner capable of scanning horses' upper limbs. Puchalski worked with Erik Bergman, DVM, Dipl. ECAR, a practitioner there, to perform her stifle lameness study.

In the retrospective study, she evaluated records from 137 lame horses that underwent CT arthrography of 141 stifle joints from 2006 to 2013. Because Warmbloods are the most common horse seen in that region and hospital, they comprised the majority (111) of the study population. The average horse age was 8, average lameness grade was 2.1 (on a 0-5 scale, with 0 being sound and 5 being unable to bear weight), and average lesion number was three per stifle.

On CT, Puchalski said, they observed :

• Most frequently, abnormalities of the meniscotibial ligaments that attach to pieces of cartilage called menisci that cushion the stifle joint (102/141);
• Lesions of any component of the meniscus apparatus (105); 
• Abnormalities of the cruciate ligaments that help stabilize the stifle (78);
• Abnormalities of the femorotibial joint formed by the femur (the long upper bone of the hind leg) and the tibia (the inner of the two bones that extends down from the knee to the hock) and its margins (73);
• Abnormalities of the meniscus (57);
• Subchondral bone changes such as lysis (decreased mineral content) or sclerosis (denser than normal bone) (27); and
• Many other injuries.

Puchalski noted that several of these abnormalities, such as those involving the cruciate ligaments, are characteristic of the Warmblood population. She said the combinations of lesions that horses had was important, and that horses with more lesions typically had higher lameness scores. "However, there are some lesions we still don't know the significance of," she added.

In conclusion, she said CT is an important method for diagnosing stifle lameness. The downside is that it's equipment-dependent.

Her practical take-away from the study is that if a horse with stifle lameness has a negative or mildly abnormal stifle ultrasound and radiographs, consider that other lesions might be present that these imaging methods do not reveal and, if possible, pursue other diagnostic options.