The Horse:Your Guide To Equine Health Care provides monthly equine health care information to horse owners, breeders, veterinarians, barn/farm managers, trainer/riding instructors, and others involved in the hands-on care of the horse.
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27 September 2016 THE HORSE TheHorse.com "Stifle injuries account for a substantial number of injuries in sport horses," says David Frisbie, DVM, PhD, Dipl. ACVS, ACVSMR, professor of equine surgery at Colorado State University's (CSU) Equine Orthopaedic Research Center, in Fort Collins. Although the exact prevalence of stifle injuries remains unknown, Frisbie estimates that approximately 40% of sport horse injuries can be associated with the stifle. Chris Kawcak, DVM, PhD, Dipl. ACVS, ACVSMR, a professor of orthopedics also at CSU, agrees that stifle injuries are a risk for any athletic horse but adds that they're more prevalent in some disci- plines than others. Veterinarians typically see them more frequently in Western performance horses, for instance, than in adult Thoroughbred racehorses. While the stifle joint's repetitive forward and backward motion during racing, or any high-speed work, can cause injury, "it's the lateral-to-medial rotational movements of Western performance horses that tend to put significant stress on the soft tissue and cartilage in the joints," Kawcak says—in other words, the quick side-to-side movements of spin- ning, cutting, and running barrels. Regardless of breed and discipline, joint anatomy remains the same, and how veterinarians diagnose and treat common stifle injuries is transferable. In this article we'll review stifle anatomy briefly and describe injury diagnosis. And while developmental orthopedic disor- ders also can result in stifle injury, they have a different cause and are diagnosed and treated differently, so we'll skip them in this discussion. We'll also describe the newest methods of treating common stifle injuries. Stifle Joint Anatomy Three bones, two menisci, and a slew of soft tissues comprise three separate compartments that make up the stifle joint. The femur, tibia, and patella (col- loquially referred to as the kneecap) form the medial femorotibial joint (at the inside of the limb), lateral femorotibial joint (at the outside of the limb), and the femoropatellar joint (located between the femur and the kneecap). Soft tissues of interest include the patellar ligaments (medial, middle, and lateral connections between bones in a joint that help a horse's stifle "lock" so he can stand for prolonged periods) and the cranial (toward the head) and caudal (toward the hind end) cruciate ligaments within the femorotibial joint. Unique to the stifle joint is the pair of cartilaginous discs mentioned earlier, called menisci, which are C-shaped and located between the two projections of the femur bone's lower end (called the medial and lateral condyles) and the tibia. One of their main functions is to facilitate frictionless move- ment of the stifle joint. Several ligaments, including the meniscotibial ligaments, hold the menisci in place between the condyles and the tibia. Finally, as in other joints, collateral ligaments located pri- marily on the outside of the femorotibial joints help stabilize the stifle. Common Stifle Injuries When we think of sports-related inju- ries, many of us immediately think of the worst-case scenarios: fractures. Femur and tibia fractures are, thankfully, rela- tively uncommon and usually restricted to trauma cases. Patellar fractures (again, following trauma) are also rare. In a study soon to be published in the Equine Veterinary Journal, Laurie Go- odrich, DVM, PhD, Dipl. ACVS, another member of CSU's Orthopaedic Research Center, and colleagues reviewed their hospital's medical records to gain more information about identifying common stifle injury types and how arthroscopy and ultrasound findings correlate. In that study they identified the menisci as the culprit in most cases. The medial menis- cus suffered injury more frequently than did the lateral meniscus, with 25 of the 47 medial menisci (53%) injured com- pared to only six out of 34 lateral menisci (17%). Other types of stifle injuries Goodrich et al. identified included: ■ Medial and lateral cranial menisco- tibial ligament tears (seen in up to 30% of horses in the study); ■ Defects of the articular cartilage—that which is in the joint—and bone cysts of the medial and lateral condyles. Again, the medial structures were more com- monly affected; 21/27 medial condyles (78%) and 15/27 lateral condyles (56%) had evidence of abnormalities; and ■ Very rarely, patellar ligament injuries. "Other potential causes of lameness in the stifle include synovitis (inflamma- tion of the synovial membrane, or the joint's inner lining) and cruciate ligament disease," says Goodrich. STIFLE ANATOMY Quadriceps femoris muscles (covering the femur) Patella Fibula Medial femoral condyle Medial patellar ligament Medial collateral ligament Medial meniscus Middle patellar ligament Lateral femoral condyle Lateral patellar ligament Lateral collateral ligament Lateral meniscus DR. ROBIN PETERSON Tibia (as viewed from the front)