Horses are known for their strength and stamina, but they also have a number of different muscles that help them move in ways most humans would find uncomfortable. The stifle, or knee joint, is one of those muscle groups that are very important to horses but can also be very problematic. Injuries to this part of the leg can be difficult to diagnose because they are so hard for horses to describe. However, ultrasound has been shown to be an effective way to diagnose stifle injuries in horses.
The stifle is the large knee in the hindleg of a horse. It is similar to the human knee, but has two extra bones in the front and back of the leg. These are called the tibia and fibula, and are comparable to our calf and shin bones. The stifle has many muscles that delicately contract and relax to help the horse stay balanced. Because of this, it can be a very tiring part of the body for a horse.
This is because it has a very high load of pressure on it, and the stifle can only be locked for short periods of time before the muscle fatigue becomes too great. In order to help reduce this muscle fatigue, the stifle has a system of muscles and ligaments that are nicknamed the stay apparatus. This includes a number of muscles that are highly fibrous and an increased capacity for blood flow, which increases their elasticity.
These muscles include the lateral and medial collateral ligaments which set the limits for the stifle movement. These are reinforced by the cruciate ligaments which connect the femur and tibia to each other. The lateral meniscus adapts the articular surface of the femur to the tibia, and the medial menisci do the same. The patellar cartilage is a strong, curved plate of fibrocartilage that fits into the trochlear groove to allow gliding movement. The trochlear groove is wide for this movement and is rounded proximally and surmounted by the trochlea tubercle.
The stifle is further reinforced by the peroneus tertius muscle, which runs between the trochlea and lateral condyles, bifurcates distally and inserts into the tarso-metatarsal region. This muscle ensures that the stifle will not be allowed to extend beyond its natural limit, and also prevents the femur from moving cranially during flexion of the stifle. Injuries to this muscle are common, as it is very strong and can cause the stifle to lock. As with other tendons and ligaments, these muscles are slow to heal, so it is very important to get a stifle injury assessed as soon as possible. This can be done through MRI or ultrasound, but ultrasound is becoming the preferred method as it does not require general anesthesia and can provide much more information than MRI in less time. A boarded veterinary sonographer is recommended to perform the ultrasound examination. These professionals are able to assess the injury and then advise you on the best treatment options for your horse.