Q. I have a 7-year-old Thoroughbred I got off the track three years ago. I had my veterinarian come out when I first got the horse to investigate a strange popping sound I heard when he turned in a small circle. My vet told me it was in his stifles and told me to adjust his diet to reduce protein, work on conditioning, and it should improve. My dressage instructor has told me that he seems to be slightly off in the hind end and suggested I get it looked at again. I've decided to get another vet's opinion about what it could be. I would like to know what questions are most important to ask, what things should I expect the vet to do when he is examining my horse, and how to be sure that this time I get answers instead of more questions.

Jessica Shier, Saint Clair, Mich.

A. Stifle problems are common in equines. Part of a complete examination would include a good set of nerve and/or joint blocks to isolate the gait deficit to the stifle joint. More often than not there are multiple areas of the leg causing pain. A systematic methodology for determining where the lameness is should be attempted.

Once the veterinarian identifies the areas of pain, performing appropriate diagnostic tests can further characterize specific causes. Conditions usually can be diagnosed with simple X rays or ultrasound; if not, a nuclear bone scan or magnetic resonance imaging (MRI) scan might be necessary.

In your horse it sounds like the classic upward fixating patella. "Popping" sounds from the stifle are almost always related to this phenomenon. There are three large ligaments the diameter of your finger on the lower aspect of the patella or kneecap. These ligaments are several inches long and run in a vertical direction. Sometimes the inside (medial) ligament gets hooked on the end of the femur.

When this happens the leg can lock in extension with the toe facing downward. In severe cases these have to be manually reduced. In my experience locking is less common than intermittent fixation, where the ligament "sticks" on the bone momentarily. When the ligament suddenly drops into a normal position, you sometimes can hear a dull "thud" sound. You can also see it easily at the walk when the patella pops into place. At the trot the hock can be seen snapping upward at the end of the stride when the patella is released from the femur. It is especially obvious when the horse is slowing down. An experienced clinician can easily diagnose fixation of the patella visually.

We commonly diagnose intermittent fixation of the patella in horses that have poor muscle tone. It is very common in horses just beginning training or those who have been out of training for some time. For these cases we advise improving the muscle condition of the horse, and most of the time they respond without incident. Exercising up hills or pulling weighted carts are a few methods recommended.

Conformation faults can predispose a horse to patellar fixation. Too little angle (straight) as well as too much angle in the conformation of the rear legs can be a factor. Cow hocks and base narrow conformation behind can also contribute. Expert shoeing to ease and square the breakover, plus providing heel support as needed, would be important considerations for treatment.

Upward fixation of the patella can also occur as a result of pathological processes in the stifle joint. On occasion, osteochondritis dissecans (OCD, a cartilage disorder characterized by the presence of large flaps of cartilage or loose cartilaginous bodies in a joint) lesions in the femur can be associated with this condition. Good quality X rays and an ultrasound examination are useful in the diagnosis. Treatments vary and range from joint injections to arthroscopic surgery, depending on the lesion.

Standing surgery can be performed to cut the medial ligament, and it will be effective in relieving the condition. However, the remaining two ligaments now are under more stress and can pull away from the patella, causing lameness. Therefore, we usually reserve this procedure for Minis, ponies, and horses that are not intended for performance.

Ligament splitting is an alternative option for performance horses and has been successful. The veterinarian performs this procedure with the horse standing, and it is an alternative if increasing the muscle tone is not effective. Other treatments include internal blistering of the ligament and intramuscular estrogen, both of which can be helpful in the hands of some veterinarians.

I hope this has been informational. Please remember your veterinarian has performed an examination on this horse and, for that reason, knows infinitely more about this case than anyone writing from afar.

About the Author

Justin Edwards, DVM

Justin Edwards, DVM, practices in Estacada, Oregon.

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