The patella plays a vital role in the horse’s hindleg action – its locking mechanism even allows him to sleep standing up. Vet Sarah Hunter explains how it operates and what can go wrong.
The patella, otherwise known as the kneecap, is a round, flat bone in the tendon part of the quadriceps muscle of the thigh.
Three ligaments are attached to it and it sits in a depression on the femur (the trochlear groove) and slides up and down within this groove as the hindleg moves.
This action enables the knee joint or stifle to operate like a hinge, allowing the leg to flex and extend but not to move sideways.
Thanks to the attachments to the tibia, the three ligaments (the lateral, middle and medial ligaments) help to keep the patella in place. They are also involved in the patella’s locking mechanism.
What can go wrong?
- Upward fixation of the patella (locking stifle) – meaning the patella is stuck in the locked position. Most cases respond well to management including the introduction of specific exercises to build up thigh muscles, though some cases will require surgery.
- Luxation of the patella – the patella slides sideways out of the trochlear groove. This condition tends to be seen in miniature breeds or foals and requires surgery to fix.
- Fractured patella – in this case the horse will show signs of lameness, with heat, pain and swelling around the area. An x-ray will determine the extent of the injury. Box rest and pain relief are common treatments.
- Osteoarthritis – this can occur following one of the conditions mentioned above, or after trauma or injury to the joint. Steroid injections into the joint around the patella can be given and, as part of the recovery, controlled exercise programmes are common practice.
There are many other injuries that can affect the stifle joint, but the key point is to identify that the horse isn’t moving correctly and ask your vet to examine the affected leg.
They will perform diagnostic tests, such as x-rays, to assess the patella and the stifle joint. Once the problem has been diagnosed, a plan can be put in place to manage or treat the condition.
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