Locking stifles or the upward fixation of the patella is often seen in the Friesian breed, sometimes simply as a short term problem in young growing horses, and sometimes as a chronic problem, especially in horses whose hind legs are very straight and stifles upright. The stifle joint itself is a very complicated body part, the equine equivalent of the human knee. The patella is in effect, the horse’s knee cap, but unlike people, horses have the ability to physically lock (fixate) their leg in the extended position by slipping the space between their ligaments over a protrusion in the bone (obviously this is a very simplified explanation). This purposeful locking of the stifle allows the horse to remain upright while sleeping or resting without falling over.
The problem occurs when in some horses, the stifle will shift into it’s ‘locked’ mode during normal movement, or will lock normally at rest but will be difficult for the horse to ‘unlock’ in order to move. The severity ranges dramatically, from a slight ‘hitching’ of the joint as the horse tries to keep it from catching, to a complete lock of the joint, so that the horse is unable to bend it whatsoever and must swing the limb out to the side by the hip in order to move and until the joint frees itself. The classic symptom of a locked stifle is apparent when a horse moves off from a stand still and the effected hind leg jerks suddenly upward. It should also be mentioned that when a horse with locking stifles has been standing in the cross-ties and a groom attempts to pick up the hoof of the effected leg, if the joint is locked, the horse will as described, jerk his leg up suddenly as the joint frees itself. This can pose some risk to the groom, but is often misconstrued as the horse purposefully kicking out at it’s handler, when it may in fact be simply the reaction of the joint.
There are varying degrees of treatment for locking stifles. The most common is a set exercise regimen aimed at strengthening the stifles and hind legs, such as working on a hill or incline and working in deep sand. Other treatments include corrective shoeing, ‘blistering’, and hormone therapy. Surgery is available but is unreversable and may cause other problems in the joint, and so should be considered as a last resort.
A temporary solution for a horse who is ‘stuck’ and cannot step forward because of the locked joint, is to back the horse one or two steps, then step forward, as this usually frees the stifle.
[AEC Client Education: Upward Patellar Fixation] – An in-depth, but easy to read article by the Atlanta Equine Clinic, describing the causes, symptoms and common treatments of locking stifles. Reccomended for those researching the problem.