Your horse’s stifle joint is the joint directly above the hock joint on the hind leg. It’s the largest joint in the horse’s body.
The stifle joint functions to flex and extend the hind leg, moving your horse along. The passive stay apparatus that locks your horse’s hind leg so the other one can rest is also part of the stifle joint’s function. When comparing anatomy to the human skeleton, the stifle joint is equivalent to the knee. However, the human knee is straight when we are standing, and the stifle is angled when the horse is standing.
Surrounding structures of the stifle include bones, muscles, and soft tissues. Above the stifle is the femur bone, below the stifle is the tibia, and the patella knee cap sits towards the front of the stifle joint.
Inside the stifle joint, there are two femorotibial joint cavities. Within each of these joint cavities, you also have a medial and lateral compartment. Also within the stifle joint, you will find menisci (cartilage discs) between the femur and the tibia. There are also two cruciate ligaments within the femorotibial joint that help the stifle remain stable. On either side of the leg, you horse has collateral ligaments. The quadriceps femoris muscle and the femoropatellar ligament keep the patella in place. The patella is also supported by three patellar ligaments below the patella.
There are many conditions that can affect your horse’s stifle joint, which will, in turn, affect his movement, comfort, and health. Leaning about these conditions and knowing what to watch for can allow your horse to have a better chance and healing and feeling well.
You may have heard of OCD, osteochrondrosis, in the stifle joint. This happens when the bones and cartilage in the joint develop unusually. Bone cysts and fragments can occur. The treatments vary from horse to horse, as does the long term prognosis for a sound horse. Age, overall health, and the specifics of the horse’s OCD play into a surgical or medical treatment plan. It’s entirely possible to find OCD in weanlings, as well as older horses.
Take a peek at the hock, here, too. So much range of motion!
You might also find a patellar luxation in the stifle joint of the horse. This occurs when the patella literally pops out of place. This is uncommon, and can be corrected surgically. For most horses, this condition doesn’t create any discomfort, but their stance is affected. The patellar luxation can happen to the side, or it can happen where the patella is lifted up, causing the leg to “lock”.
Horses can also have stifle injuries involving the bone, such as a fracture, or a tear in the soft tissues (ligaments, tendons, muscles). Kicks to the stifle are often the culprit here, as are running and jumping. Long term wear and tear as well as acute injuries can damage the stifle joint and surrounding tissues.
There is also the case of a horse that finds himself tangled in fence, or has a cut puncture near the stifle joint. Infection is a real threat, and can permanently damage the stifle joint. Really, any cut or wound can become infected, and when this happens over a joint, things can go sideways in a bad way quickly.
As with other joints, the stifle can develop degenerative joint disease. This DJD usually has it’s start with arthritis and ligament injuries.
Ice therapy reduces inflammation!
So - now that we have had a primer into the stifle joint - how you do know what’s going on in there?
Your daily grooming routine should include using your hands and eyes to cover every single inch of your horse! Feel for heat, swelling, tenderness, cuts, scrapes, anything unusual on the actual joint.
But - you may also find your horse is sore in his back - specifically the croup and loins (loins are directly behind the saddle, keep going to the tail for the croup). Hind leg problems are often transmitted to your horse’s back.
On the ground - do you notice if it’s harder for him to pick up one hind leg? What about turning around in his stall, is it easier in one direction than the other? What about how his hoofs track up when he walks next to you? Does one hind hoof overtrack the front, when the other hind hoof doesn’t overtrack at all?
Stifle issues also show up as a lameness. For a rider, the canter is the gait where you will feel and see trouble. Cantering on one lead is harder, picking up the canter is difficult, shifting from trot to canter is hard. Also consider “cross firing”, the case where your horse will have the correct lead up front but the wrong lead behind. Bending is also tricky.
Conformation also plays a part. If your horse is post legged, his stifles are more susceptible to problems.
The patella is on the left of the joint in this photo.
Ultimately - it’s up to you to read his body language during grooming and interpret his “training issues” as a sign that something is wrong. As always, work with your Veterinarian to get to the possible causes of anything weird that you find. Keeping in mind that it’s proven fact that the longer you wait, the more expensive the Vet bill is, make the call early!
There are many things you can do as a horse owner to stay ahead of issues in your horse’s legs, one of them being just paying attention! Also preventative care, like ice, can go a long way to reduce microscopic inflammation that becomes an issue later on. Don’t forget about a safe training plan, daily turnout, and a balanced diet. Lameness exams (even if your horse appears to be sound!) can spot issues before your horse says “NO” and major damage has occurred.
It really just boils down to being informed about your horse, and using prevention to keep him healthy, instead of waiting until he’s visibly lame.