By Garrett Metcalf, DVM
No horse owner wants to hear that their horse may have a stifle injury, but when it does occur you can hopefully rest a little easier after reading this article. There is a fair amount of misnomer, hearsay and what it can mean for the horse if they suffer a stifle injury. Used to be common thought when a horse was “stifled,” that the horse’s career was over, and the horse was unusable, but that stigma about a stifle injury is no longer true. The stifle is one of the most complex joints that horses have and a large contributor to the locomotion that a horse needs to perform and do large amounts of work in the hind limbs. The stifle, no doubt, has its own set of problems, but veterinarians have grown to understand this joint and its problems much better in the recent decade or more through research, advancement in diagnostic techniques and treatment options.
The equine stifle is built very similarly to the human knee. It has a patella, menisci and cartilage very much like our knee, but the equine stifle is divided into three different joint compartments. These are the medial (inside) femorotibial, femoropatellar and the lateral (outside) femorotibial joint compartments. The joint compartments that get the most attention and have the most problems are the medial femorotibial and femoropatellar joints. These two compartments share the same joint fluid in approximately 67 percent of horses. The equine stifle also has cruciate ligaments just like the human knee that are commonly referred to in humans as ACL and PCL ligaments, but thankfully they are not as commonly affected in horses as they are in people.
Stifle issues can start at birth due to developmental orthopedic issues or occur as injuries later in life. The lesions that arise from birth or as neonates are part of the developmental orthopedic complex, which includes osteochondritis dissecans (OCD) or subchondral bone cysts. The cause of these lesions is not fully understood and is believed to be caused by multiple factors. Factors such as nutrition, genetics and trauma/exercise have been incriminated in causing the development of these orthopedic lesions. There are common locations that these lesions develop in the stifle joints of horses. The OCD lesions are commonly found in the femoropatellar joint in specific areas on the femur bone called trochlear ridges. Bone cysts form in a different location on the femur, most commonly in the medial femorotibial joint.
Stifle injuries can occur in any horse and any discipline, but these injuries are more commonly seen in western performance horse such as reining horses, cutting horses, rope horses and barrel horses. These disciplines that demand a lot of work from the hind limbs can lead to injuries to the stifle joint. Common stifle injuries are damage to the articular cartilage, straining or tearing of ligaments that hold the menisci in place or tears in the menisci themselves. The joint that takes the blunt of the work and most often has the most injuries is the inside joint or the medial femorotibial joint compartment. This compartment contains the medial meniscus where a lot of wear and tear takes place.
Read more about equine stifle injuries in the February issue of Oklahoma Farm & Ranch.