The locking stifle is an evolutionary adaptation that allows horses to sleep standing up. Vet Gil Riley shares how the locking mechanism can go wrong, and treatment options for when it does.

The stifle is the area where the tibia meets the femur, and is the equivalent of our knees — when you pick up a horse’s hind leg, the joint bends forwards, just as our knees do when we walk up stairs.

When horses roamed wild, this ‘locking’ of the joint meant that when a predator attacked, a horse could go straight into gallop, while other animals who had to lie down to sleep were left scrambling to their feet, and thus were an easier target.

The stifle locks through one of the three ligaments that attach the patella — or kneecap — to the tibia, slipping into a groove on the inside of the femur (thigh bone).

Sticky stifles

In a normal situation, the stifle will only lock when the horse or pony is stationary, and release immediately when the animal starts to walk.

Sometimes, however, the patella will not release immediately, or may catch occasionally during walk. This is sometimes referred to as a ‘sticky stifle’ and must be uncomfortable for the affected animal.

A locking stifle can be referred to by vets as an upward fixation of the patella, and reasons why the patella may start to stick include:

  • As a young animal grows, there may be phases when the angle of ligament to the femur allows a catching during walk. Such cases usually resolve as the animal matures.
  • Sudden weight loss or weight gain can also change the forces around the stifle, causing it to lock when walking.

Steps to recovery

There are various treatment options, and these include exercise involving hill work to build the quadriceps muscle, and giving a muscle supplement to increase the pull on the patella from the quadriceps, thus making the ligament less likely to catch at walk.

Other treatments include ‘splitting’ the patellar ligament. This is a minor surgical procedure carried out under sedation that encourages the ligament to scar and makes it less likely to catch.

Finally, oil/formalin can be injected into the ligament to cause scarring and make it less likely to catch.

Corrective shoeing

Correct shoeing can aid a horse with locking stifle.

“Horse owner, vet and farrier, working together, can definitely help to improve locking stifles,” adds Your Horse farrier Dale Beecham. “Close inspection of the horse’s gait, wear patterns on his shoes and feet, and any underlying reasons for the locking stifle, such as conformation and workload, can all be used to make a shoeing plan.”

Main photo = stock image (copyright Kelsey Media Ltd)

About the expert: Gil Riley MVB CertEP MRCVS is a vet at Pool House Equine Clinic in Staffordshire, and a former Petplan Equine Vet of the Year. 

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