Upward Fixation of the Patella

...and on the eighth day God created the horse in perfect image, to romp, graze, gallop, play and make manure wherever it darn well pleases, in divine grace.

Continuing our series of short articles, this week we will look at Upward Fixation of the Patella.

Just what is Upward Fixation of the Patella?

It is also called “Stifling,” because it involves the stifle, and it happens when the joint is fully extended.

This is not to be confused with “Luxation of the Stifle Joint.” (Dislocation.)

The patella becomes fixed at the top of the ridge of a tract-like rounded projection called the trochlea of the femur, and it is caught between the medial and middle patellar ligaments. (1)

Some of the causes for the patella becoming fixated in this position are trauma to the hind leg when the limb is overextended, poor conformation, especially if the hind legs are too straight and loss of strength in the animal. Poor conditioning also makes the horse predisposed to Upward Fixation of the Patella. (2)

Once this has occurred, the ligaments become stretched and the horse will be subjected to a recurrence of the problem.

The way to tell if the horse has Upward Fixation of the Patella is that its hock joints and stifle will be locked in a fully extended, outward position, with no flexibility. The front of the foot and the fetlock will still have flexibility, and these will be able to rest or position on the ground. (3)

If the horse is driven forward, the front of the hoof will drag on the ground.

When the leg is locked in this extended position, palpation of the stifle by the Veterinarian will show that the patellar ligaments are tense, with the patella locked above the medial ridge of the trochlea of femur

This issue is unpredictable in that the condition may remain stuck in the extended position for several days or just hours, or it may unlock almost instantly. (4)

Sometimes the condition may be confused with Stringhalt, because there is a momentary catching of the patella when the horse moves forward. The sudden upward jerking of the leg when the foot leaves the ground will be noticed on the horse’s forward stride, in the first few steps.

It is very noticeable when the horse is on the lounge line working in circles.

Sometimes the catching of the patella is accompanied by a cracking sound each time, as the patella is released.

In other cases, the horse can have Upward Fixation of the Patella in both legs. This can be extremely painful for the animal and usually results in rapid breathing and sweating, due to the pain. His own heavy weight works against him on the affected legs; usually the animal is unable to move.

The Veterinarian may do a test to aid in the diagnosis.

A serious knowledge of the anatomy of the stifle is required to correctly apply the mechanical forces necessary for a remedy. Treatment depends on the frequency of occurrence and the severity of the problem.

The Vet will talk with you about the animal’s medical history to determine the best course of action, and surgery should only be done by a qualified professional.

On a first time occurrence, the Vet might tranquilize the horse to attempt to replace the patella mechanically.

A rope is fastened below the fetlock and the leg pulled forward, while at the same time pressure will be applied to the sides of the patella in an outward, upward direction to dislodge it. (5)

The hock and stifle joints will flex when the patella is returned to its correct position.

In a small percentage of cases, driving the horse forward or backward suddenly and quickly can force the patella to slip back into place.

In rare cases, the Vet may administer a general anesthetic in order to fully relax the muscles and allow replacement of the patella.

If the animal has repeated occurrences of Upward Fixation of the Patella, the Vet will do surgical procedures.

This operation is called a Medial Patellar Desmotomy, or cutting of the Medial Patellar Ligament.

The operation works on the principal of the Medial Patellar Ligament being responsible for holding the patella in an upward position, so severing this ligament will make fixation mechanically impossible. (6)

It sounds worse than it really is, and does not impair normal function; horses actually do quite well after surgery, even in strenuous workouts.

Prognosis is good. Surgery can correct most cases.

However, there is risk of arthritis of the stifle joint or chondromalacia(pain) of the patella in long-standing cases. This could result in persistent lameness, even after surgery. (7)

They can never stand up to sleep again, as horses do, since the locking mechanism has been removed.

I have seen this on a horse before. It looks peculiar, with the animal dragging its hind limb around behind. It makes work outs tedious.

In older years, this particular horse eventually had to be put down, because it could not get up from the laying position on its own anymore.

The medical condition described in the aforementioned article is meant as a guideline and not Veterinary analysis.

Always consult a qualified Vet if you suspect your horse has Upward Fixation of the Patella.

Leaving February behind with the rest of the Wee-belows, ( a wee below 0 degrees or a wee below -2 degrees) to the immortal words of Roy Rogers and Dale Evans, “Happy Trails to You.”

1 - 7: “Horseman’s Veterinary Encyclopedia,” by Will A. Hadden III, DVM