The patella is in your horse’s leg and the equivalent to a person’s kneecap. Vet Gil Riley explains what can go wrong with the patella, from locking stifles to injuries from kicks.
The patella is involved with the locking mechanism of the stifle, which allows the horse to sleep standing up. The locking mechanism is when one of the three ligaments that attaches to the patella to the tibia slips into a groove on the inside of the femur (thigh bone).
1. Sticky stifle
In a normal situation, the stifle only locks when the horse is stood still and will release immediately when they begin to walk. However, sometimes the patella will not immediately release; this is known as locking or sticky stifles, or upward fixation of the patella.
The patella may stick in a young horse when as the horse grows, there may be phases when the angle of the ligament to the femur allows it to catch during walk; this usually resolves as the horse matures.
The patella may also stick following sudden weight loss or gain, as the forces around the stifle change.
2. Failure to lock
The patella may also fail to lock. This could be the result of poor conformation, where the patella and its attached ligaments do not quite manage to catch over the ridge in the femur.
Failure of the stifle to lock may inhibit the horse’s ability to sleep standing up. Fortunately this is not a common condition, and affected horses will lie down to sleep.
3. Chips or fractures
The patella can get chipped or fractured. A kick to the front of the stifle, or the stifle striking a fence when the horse fails to clear a jump, are the most common reasons for injury.
A chipped or fractured patella will require surgery, either to remove the fragments or, in the case of a major fracture, it can be an option to fix the patella together with a screw.
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.