If you cannot see images at all on my site click here for an explanation
Medical Index
Posted May 2007


by Debora Johnson

The stifle joint in a horse is very much like your "knee." It is a complex structure and is subject to many problems. The stifle is found on the horse's hind legs. Just an interesting note about the horse's forelimb "knee." It works more like a human wrist.

Structural Description


Two individual joints make up the stifle. Where these two bones join is the area of the stifle. The femoral-tibial joint is used to communicate between the large bone in the upper (femur) and the smaller bone below it (tibia). Communication from the patella or kneecap is sent to the femur through the femoral-patella joint. The stifle is made up of these two joints. A thin capsule surrounds the entire stifle joint that has a specialized fluid to help with shock absorption and lubrication.

The ligaments in this joint provide stability to this structure. The ligaments (collaterals) keep the leg from bending too much in either direction. They are found on the inside and the outside of the stifle. If your horse falls, slips, or wrenches these ligaments they can tear.

In the center of the stifle joint you can see two large crossing ligaments (cruciate ligament). These two ligaments form an X inside the joint by attaching to the femur and tibia. They also prevent the leg from bending excessively. Cruciate ligaments are easily damaged.

While standing, the horse is able to lock his hind legs by shifting his weight and rotating the patella. This action locks three patella ligaments over a ridge located on the femur (trochlear groove). Horses have 3 distal patellar ligaments: the medial patellar ligament, the middle patellar ligament, and the lateral patellar ligament. This is what allows the horse to sleep while standing. Sometimes there is a defect in this mechanism. Once this locking takes place the horse is unable to release the locked limbs. Chronic weak stifle is often due to a general lack of muscle tone in the hind limbs. That is aggravated by poor confirmation (very straight and upright hind legs), deep footing, poor shoeing (too much toe or extended heels), or pre-existing hock or fetlock arthritis. Stifle joint problems (OCD, arthritis, cruciate ligament) are also a main source of stifle problems.


The stifle is a complex joint that carries a lot of weight. There are two thick pieces of C-shaped fibro cartilage that act as shock absorbers. They are located between the femur and the tibia. This cartilage is called menisci. Wear and tear on the cartilage surface of the joint are minimized by the menisci. They also act as stabilizers to the joint. The menisci act to distribute weight on the stifle joint.. Between the ends of the femur and the tibia there is two thick pieces of C-shaped fibro cartilage that help act as additional shock absorbers. If the menisci are damaged it can result in a lame horse.

Upward Fixation
Study: Surgery to Fix Patella Problem Often Successful

Sometimes a horse will have a slight hitch in the gait which is subtle. It is more noticeable going downhill. This condition can also be severe. The leg may lock out behind the horse. When this happens the leg is unbendable. The leg may drag or point in a backward position. This condition is called upward fixation of the patella. I have owned two horses with this problem.

  • Non-weight bearing pelvic limb lameness
  • This may be distinguished from tarsal (hock) soreness which is usually weight bearing in nature.
  • The horse will frequently drag the toe of the affected limb(s) during exercise.
  • Visible wearing of the dorsal aspect of the toe/shoe may be apparent.
  • The foot of the affected limb(s) will have a low-arc flight pattern.
  • The horse will usually exhibit a shortened cranial phase to the stride.
  • Resistance in the canter.
  • The horse will resist the canter, particularly if circled toward the more affected limb.
  • Resistance may be most noticeable during the transition between the trot and canter, when the horse is forced to extend the pelvic limb for a prolonged period.
  • Many horses will toss their head, rear, or stop when asked to canter. This may be due to their "anticipation" of impending upward patellar fixation.
  • The horse would rather trot than canter. (Trotting is harder for the normal horse)
  • Consistent lead changes or cantering on the wrong lead.
  • The horse avoids prolonged pelvic limb extension with the affected limb. This is particularly apparent when cantering in a circle towards the affected limb.
  • The canter is very rough or "bouncy."
  • This occurs as a result of consistent delay in pelvic limb flexion from the extended position.
  • Swelling, heat, and/or pain may be associated with one or both stifle joints.
  • Upward patellar fixation causes patellar instability which in turn may result in femoropatellar synovitis.
  • The horse drags his hind toes during exercise.
  • Resistance and/or difficulty when walking up and down hills, or when backing up.
  • These situations force the horse to extend the pelvic limb for a prolonged period. Rather then fully extend the pelvic limb(s), the horse may "crouch" while walking. Rather than flex the pelvic limb(s) normally, horses will often swing their limbs to the outside. This may cause the lameness to be confused with neurologic disease. (such as EPM or stringhalt).
  • Lameness is most severe when the horse is first taken out of the stall.
  • Many horses will improve as the workout progresses.
  • Lameness becomes more obvious following an extended period of stall rest.
  • Loss of muscle and patellar ligament tone exacerbate the upward patellar fixation.
  • The horse does not improve (and may worsen) as a result of taking time off.
  • The horse does not respond to anti-inflammatory (e.g. Phenylbutazone) therapy.
  • Intermittent upward patellar fixation is a mechanical problem and is not inflammatory-mediated.
Pet Care Tips

As with many cases of pelvic limb lameness, secondary abnormalities such as thoracolumbar ebaxial (back) and proximal thoracic suspensory ligament soreness are also present. These are generally detected during the passive lameness evaluation and are suggestive of chronic pelvic limb asymmetry/ lameness.

  • Osteochondritis dissecans (OCD) lesions
  • Osteochondritis dissecans (OCD) lesions
  • Horses with persistent bone microtrauma
  • Upward fixation of the patella
  • Miniscal damage
  • Cruciate and anterior ligament damage
  • Chondromalacia (softening of the articular cartilage) due to chronic repetitive trauma

Typical treatment of upward fixation is the use of anti-inflammatory medications (NSAIDs), hand walking followed by a conservative rehabilitation program, therapeutic shoeing, and sometimes an internal blister is necessary to manage a recurrent and persistent case. Whether you're dealing with a mild or more severe case, physical therapy exercise should include long periods of low-intensity work and hill work to strengthen the quadriceps muscles. Some practitioners have had success with intramuscular estrone (related to the estrogen estradiol) injections for its anabolic effect on increasing muscle tone, particularly in geldings. A surgical procedure of splitting of the medial patellar ligament might induce thickening and stretching of the ligament.

Management of stifle synovitis and arthritis is similar to therapies suggested for hock lameness--IA steroids, IA hyaluronic acid, systemic anti-inflammatory medications, systemic joint therapy, arthroscopy, shock wave therapy, and acupuncture.

  • Lack of fitness Lack of quadriceps and/or biceps femoris muscle tone results in an inability to quickly pull the patella up and off of the medial femoral trochlea.
  • Straight or upright pelvic limb conformation This places the medial femoral trochlea further distad in closer proximity with the patella, facilitating patellar fixation.
  • Excessive distal patellar ligament length This places the patella proximad in closer proximity with the medial femoral trochlea, where it can inadvertently "catch" or "lock." The factors which cause upward patellar fixation are often interrelated. An unfit horse will generally have increased laxity (increased length) of the distal patellar ligaments. Neurologic disease can also cause a lack of fitness. Intermittent upward fixation may also occur secondarily.
Hind End Conformation

  • A Hind leg too straight Commonly known to be one prone to upward fixation of the patella. It can lock and become a chronic problem. The lack of proper angulation in the leg can also create too much concussion straight down through the hock.
  • Stands under (sickle hock) This type of structure is known to be one creating possible hock issues such as arthritis and/or spavins due to the strain placed on the back of the hock.
  • Camped out This conformation has the potential for hock problems. (Arthritis and spavins). A horse who is camped out cannot support his weight correctly. Balance of the hindquarters may be a problem.
  • Cow hocked Cow-hocked conformation creates undue strain on the inside of the hocks and stifle. There is an arc from the stifle to the hoof. It is also common to see a twisting of the hocks which has a wrenching effect to the hip joints, stifles and hocks.
Treatment Options
  • Exercise Lack of fitness results in decreased thigh muscle and patellar ligament tone. With decreased supporting muscle and ligament tone, it becomes easier for the patella to lock on the femur and harder for it to replace within the trochlear groove. In subtle cases of upward patellar fixation where conformation is relatively good, increased exercise alone may result in resolution of the problem. Ligament splitting is an alternative option for performance horses and has been successful. The veterinarian performs this procedure with the horse standing, and it is an alternative if increasing the muscle tone is not effective.
  • Corrective Shoeing Since fixation of the patella occurs when the pelvic limb is extended, prolonging the extension phase of the stride can make "unlocking" more difficult. Alternatively, shortening the amount of time the pelvic limb spends in extension allows the horse to unlock his/her patella before the distal patellar ligaments become excessively tight. Since the conformation of the distal pelvic limb and/or the toe length is intimately related to pelvic limb breakover, the farrier can frequently alleviate the problem via corrective trimming/shoeing. Rolling and/or rockering the toe of the shoe, applying a full (egg-) bar shoe, and/or the use of wedged pads (when needed) are commonly used techniques. In many cases, we are able to help the pelvic limbs break over before intermittent upward patellar fixation occurs. My two horses responded well to this fix. My farrier, Don Roof, elevated my horse's hind limbs, with pads, about 3 degrees. Both horses moved soundly immediately.
  • Hormonal Therapy The administration of estrogen has shown to prove beneficial for some horses exhibiting intermittent upward patellar fixation. The presence of estrogen within the body of the horse may increase tension of various supporting ligaments. These include the collateral, suspensory, cruciate, and distal patellar ligaments. Increasing distal patellar ligament tension helps to relocate the patellar further distad, thereby making upward patellar fixation more difficult. This in turn may alleviate clinical signs. It should be noted that estrogen is also a powerful behavior modificator in the horse. It is often used for stallions and geldings that are excessively difficult to handle, aggressive towards people or other horses, or overly anxious at shows and other events. Estrogen is very effective at reducing anxiety and resistance as well as improving overall behavior in these horses. Treatment usually consists of 2 injections of estrogen (25mg) in the muscle twice weekly for 4 consecutive weeks, then as needed thereafter.
  • Administration of estrogen to mares usually causes them to exhibit clinical signs of estrus (heat). Since this change in behavior is generally undesirable, it is not recommend for use in mares.
  • Intraligamentous Infusion of Counterirritant This form of therapy is usually referred to as "blistering." Blistering involves the injection of an irritative substance into soft tissue(s) in an attempt to create an inflammatory reaction. The irritative substance usually consists of iodine 2% in an almond oil base. This substance can elicit an inflammatory response for up to 30 days depending on the amount used and the location of injection. It is important to remember that fibrosis and scar tissue formation within normal soft tissues will occur as a result of severe inflammation. Scar tissue does not function like normal soft tissue. Blistering in certain areas may inhibit proper function of associated soft tissue. It is not generally recommended.

However, in the case of intermittent upward patellar fixation, we gain a biomechanical advantage by replacing normal tissue with scar tissue. The infusion of counterirritant within and around the medial and middle patellar ligaments results in the elicitation of an intense inflammatory reaction by the horse's body. With inflammation, fibrosis and scarring of the patellar ligaments occur. During the scarring process, soft tissues will contract (shorten). As the patellar ligaments shorten, the patella is pulled up and over the hook of the medial femoral troche and into its normal position within the trochlear groove. At this point, it becomes more difficult for the horse to lock the patella and easier to flex the pelvic limb from an extended position. This from of treatment has been extremely effective in a vast majority of cases involving intermittent upward patellar fixation. This has to be done carefully by skillfully trained individuals.

Medial Patellar Desmotomy

The medial patella ligament is one of the key structures (along with the patella and middle patellar ligament) that is required to lock the patella on the femur. Since the problem represents the horse's inability to quickly disengage the patella from the medial femoral trochlea, surgical resection of the medial patellar ligament results in complete resolution of the problem. Once the medial patellar ligament is resected, upward patellar fixation becomes impossible and the clinical signs associated with this condition disappear. Consequently, this has become a very popular form of treatment for horses with intermittent upward patellar fixation. It is extremely important to note, however, that the medial patellar ligament also performs another function: stabilization of the patella within the trochlear groove of the femur. Without tension from the medial patellar ligament, the patella becomes unstable within the femoropatellar joint. Femoropatellar synovitis and frequently osteoarthritis result. Since the stifle is high-motion in nature, chronic inflammation within this joint poses a significant concern in regard to future performance soundness. Persistent femoropatellar joint inflammation typically needs to be addressed on a continual basis and often requires considerable maintenance therapy. It is for this reason that The Atlanta Equine Clinic views this form of treatment inappropriate except for the most severe of cases that have proven refractory to the other forms of therapy. Atlanta Equine Clinic

Ligament splitting is an alternative option for performance horses and has been successful. The veterinarian performs this procedure with the horse standing, and it is an alternative if increasing the muscle tone is not effective. Other treatments include internal blistering of the ligament and intramuscular estrogen, both of which can be helpful in the hands of some veterinarians.

Radiographic views are essential to identify some of these conditions. Ultrasound is helpful to assess soft tissue and early bone responses. More information is available at this link: Diagnosis and Treatment of Stifle Lameness

Note: I have had several horses that "hitch" from stifle. My farrier raised the angles of the back hooves by 2 degrees and farried in a "Rocker Toe" I worked the horses up hills and built up muscle. Going down hill I worked them slowly. The hitch disappeared in all 3 of these horses.

Note: "Does a horse ever get over a stifle?

"Stifle injuries in the horse range from minor to very severe. If your horse is locking its patella, the prognosis is very good with proper treatment. If your horse has ruptured ligaments or a torn meniscus, the prognosis is more guarded and will likely require surgery. OCD cysts of the stifle can be successfully treated if there is no arthritis present. Arthritis of the stifle has a poor prognosis for athletic soundness. Your veterinarian will be able to determine the type of injury and prognosis. Manuel Himenes, DVM, Kailua, HI" AAEP/Ask the vet

For More Information:

Unlocking Stifle Proglems
Hock and Stifle/A Gaited Horse Issue
The Conservative Approach for Healing Horses
Stifle Problems

Medical Index