Description

A locking stifle in a horse affects the stifle joint which includes the kneecap and ligaments and is the most complex joint in the horse. In horses with this condition, one of the ligaments in the kneecap catches over the inner ridge of the femur. This causes the hind limb to be locked  while extended.

The horse's toe then drags as the leg is moved forward and flexion appears exaggerated. A clicking noise may be heard as the horse moves. In some cases, the ligament does not release from the femur and the hind limb becomes locked in extension.

Also referred to as intermittent upward fixation of the patella (UFP), the condition causes a slight delay in flexion of one or both hind limbs.

Young horses and horses with poor limb conditioning or a straight conformation of the hind limbs are more prone to locking of the stifle joint.

Symptoms

• Intermittent catching of the ligaments of the patella over a protrusion on the lower part of the femur
• A delay in smooth flexing of one or both hind limbs
• Dragging toe
• Clicking noise as ligaments catch and then release
• Uneven gait

Causes

Horses with straight stifle joints are more prone to this condition than other horses. Locked stifle can also be caused by injury to the kneecap and ligaments, degenerative arthritis, or stifle joint swelling.

Prevention

Keeping horses in good physical condition, with proper exercise and nutrition for good muscle tone and strong joints, will help prevent this condition. Persistent cases that are not resolved by an appropriate exercise regime may require surgery.

Treatment

With a horse that has a locked stifle, a maneuver that will release the locked kneecap is as simple as backing the horse while at the same time pushing inward and downward on the kneecap.

Increased physical conditioning may be helpful in improving muscle strength and tone and may keep the patella from locking up. In other horses, a veterinarian may use an irritant to alter the pull of the patella and aid in preventing upward locking.

Surgery is recommended for horses that have recurring problems with locking stifle. The surgery is known as medial patellar desmotomy and is relatively simple. It is usually performed on the standing horse and involves cutting the ligament that catches on the femur. Recovery can take several months, depending on the horse, but some studies have shown a 98% success rate.