A complication that can arise to the standing up, sleeping horse

The horse has the capability of staying in a standing position for very long periods of time, and may even sleep standing up. This can be done by a particular characteristic of its anatomy at the level of the stifle (same as our knee, positioned at about the level of the horse’s flank). The horse usually “locks” and “unlocks” its stifle without any difficulty while the animal is standing. The reciprocal apparatus is the system that permits a horse to stand for long periods of time without using too much energy. It is composed of tendons, bones and muscles and when the knee cap or patella locks in a certain position within the stifle, the hock (the joint that is the same as our heel/ankle joint positioned approximately 24 inches from the ground on the hind leg) is extended but it cannot bend. Therefore, this apparatus when “locked” holds the stifle and hock in extension, and when its “unlocked” the stifle and hock can be flexed. The patella is attached between the femur and the tibia by 3 ligaments.

Diagnosis: Upward fixation of the patella

When a horse suffers from this condition, the knee cap and associated soft tissue structures “lock” over the inside portion of the femur where it should instead slide. This results in the inhibition of the flexion of the hock and stifle. The horse acquires a typical stance with an extended leg and when attempting to walk it flexes the fetlock (ankle joint that is approximately 8 inches from the ground) and drags the foot on the ground. This is usually non painful, but some horses get very nervous trying to free themselves from their locked joints. This condition can come and go as well, where the horse releases the leg with audible “popping” noises and jerkiness to the leg.

This pathology is most commonly seen in young horses. Some factors that could predispose this condition are poor muscle tone and condition, straight hind limb conformation, trauma to the region and hereditary factors.

Complete physical exam along with radiographs of the stifle are diagnostic and necessary to rule out any other pathology or joint disease.

Therapeutic treatment

If your horse is completely locked up, you can usually get them to unlock by backing them up a few steps. Most horses improve after appropriate conditioning and developing of quadriceps muscle tone with training. This is best accomplished with hill work, but in the Midwest we sometimes will have to compromise and pull logs instead.

Other conservative but more invasive option of treatment is the injection of compounds in and around the medial patellar ligament in order to tighten it up, enabling it to glide without catching on the medial femur.

A third method of treatment is the administration of estrogen intramuscularly to the horse which has anecdotally shown to be beneficial. This therapy is confusing to some, but seems to increase tension of the patellar ligaments making upward patellar fixation more difficult.

When these conservative methods of treatment have failed, surgery should be considered.

Surgery

There are two described methods of treatment of this condition. One is the medial patellar ligament transection and the other one is the medial patellar ligament splitting. The first surgery involves the cutting of the ligament where in the second surgery small incisions are strategically made over the ligament which will ultimately cause the ligament to tighten.

Both surgeries are performed with the animal standing under sedation and local anesthesia and as an outpatient basis, although some surgeons prefer to do them under general anesthesia.

If surgery is necessary, prognosis is favorable. Post-operatively some high level exercise horses may rarely develop a pathology called “distal fragmentation of the patella” which is the development of small spurs and bony fragments at the end of the patella that can bring pain and lameness to the horse. This condition, although rare, can be very alarming especially if your horse completely locks its stifle causing them to drag their leg behind them. Just remember not to panic and back them up a few steps, followed by an examination with your veterinarian to provide the best treatment plan.

Due to their long, straight backs, horses can’t get up quickly. If a predator approaches a sleeping horse while it’s lying down, the horse may not be able to get up fast enough to escape. Thanks to specialized legs, however, a horse can lock its knees and fall asleep standing up — without falling over! Unfortunately these God given talents can also have their occasional flaw. That is why God also created the Veterinarian!

Dr. Darin Peterson, DVM, was born and raised on a horse and cattle ranch in Rosholt, S.D., and received his B.S. in Animal Science from SDSU. He concentrates most of his work time with large animals. He can be reached at 701-347-5496 or dpeterson@cassvetservice.com.