Locking patella, more properly known as intermittent upward fixation of the patella is an interesting issue in horses as part of the horse's ability to sleep or rest while standing up is directly related to their ability to "lock" their knees to keep them upright. Locking stifle becomes a problem with this locking mechanism and actually kicks in while the horse is moving or wants to move.
Locking stifle is noticed in either one or both back legs and is more problematic in horses with poor conformation on the hind end. Often horses with post-legs or very straight hind legs will have more problems with locking stifle. The first signs that the owner may notice is a dragging of the toe of the hind leg or legs and a slight hesitation in the bending motion of the hind leg when the horse is moving forward. Occasionally flexion may seem very extreme and exaggerated and a loud popping or clicking sound can be heard as the horse moves. In severe cases the leg may become locked and horse cannot disengage the lock, resulting in a very extended back leg that appears to be paralyzed. Although this looks horrible simple massaging and manipulation of the leg, your vet can show you the exact method, will cause the stifle to unlock and allow the horse to move normally.
One of the best treatments for mild cases of locking stifle is to provide a regular exercise program that will improve the muscle tone in the hind quarters to allow the horse to be able to disengage the locking stifle on their own. This exercise can include longer walks or jogs, trail riding or increased pleasure riding as well as dressage or other forms of training that will increase the muscle tone of the horse on a gradual basis.
A surgical procedure known as medial patellar desmotomy or MPD is often complete in cases where the condition is chronic and does not respond to increased muscle development in the legs. This is a relatively simple procedure that involves cutting the ligament that is catching on the femur and causing the movement problem. Most horses respond very well to this surgical procedure and are able to continue on as competition or pleasure riding horses after they have recovered. Some horses will have increased lameness and ongoing patella problems after the surgery so most vets will only use this option as a last resort.
Since the greatest cause of locking stifle is a conformation problem, breeding for good conformation in any breed is essential. In some of the breeds that are prone to straighter back legs careful selection of both stallions and mares is essential to avoid contributing to any problems that foals may experience due to the lack of conformation that is inherited through breeding lines.
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