The stifle is the largest, most complex joint in the horse, and problematically the weakest. Anatomically this joint corresponds to the knee joint in humans. For treatment of the human knee in physical therapy it is well established that the quadriceps muscle plays a pivotal role in the alignment of the patella for proper knee function. The same is true of the horse. Results can be devastating for the stifle when quadricep function declines due to lack of activity, growth spurts, or injury. This leads to stifle pathomechanics of the patella getting “stuck” on a bony protrusion of the femur, resulting in debilitating pain, swelling, and reduction in functional locomotion. Historically various invasive surgical procedures and a multitude of suggestions for conditioning exercise have had less than favorable results. Until the recent decade, not much has been offered to the equine in the way of rehabilitation for this scenario.

The stifle is the largest of all joints in the equine and has the most elaborate of all the articulations1. The stifle is also known as the tibial femoral joint in the horse. Due to anatomical structure of the stifle, and its location, it is the weakest joint of the horse. The stifle joint is made up of four bones the femur, the tibia, the patella and a remnant fibula.

The fibula is a non-functional bone that is fused onto the tibia. The patella, a sesamoid bone, submerged with in the quadriceps tendon, functioning as a pulley, similar as in the human knee and quadriceps. The patella’s smooth movement depends upon the normal function and strength of the quadriceps muscles the tensor fascia latae and biceps femoris.

The muscles that support and connect to the stifle joint play a vital role of health and function of the patella. They keep it tracking optimally for the greatest functional performance of the joint, contributing to the power of the “hind end engine”. If the muscles previously described have adequate force and the timing, the contraction is adequate, and there are no other conformational,

ligament or joint pathology involved, than chances of the patella getting hung up for a fixed period, or intermittently, is significantly reduced. Maintenance or conditioning of these muscles is important. The before mentioned muscles have a direct attachment and therefore direct affect on the patella and stifle joint of the horse. There are many other muscles that play a significant role in flexion and extension of the joints of the hip, stifle and lower leg, with multiple actions played by each, but their significance is beyond the purpose of this case study.

IUFP occurs when the patella fails to disengage from the medial trochlear ridge of the femur due to ineffective contraction of the stifle extensor mechanism at initiation of attempted limb flexion just seconds before the motor command for the horse to take a step forward with the rear leg. Failure of this mechanism to release the patella with in the joint, causes the

stifle to become fixed in extension, disallowing the lower leg to move into elevated flexion, therefore dragging the hoof and toe along the ground. Flexion of the leg is not possible until the patella returns to the inter-trochlear groove which is then followed by limb hyper flexion. This is a dangerous situation for both horse and rider if the horse is being ridden. IUFP is when the patella releases spontaneously, but locks again in variable intervals in forward movement (gaits) of the horse.

Several factors of pathogenesis come into play contributing to IUFP. Most common is

the anatomical design  or conformation, (similar to posture in humans) of the horse’s hind leg. Ideally the articular angle of the stifle joint should be about 150 degrees. A leg with decreased angulations formed by the interplay of joints of the pelvis, hip, stifle and hock (excessively straight hind limb) is more prone to stifle problems. This can be due to heredity (genetics) or breed dominant traits. A horse that has low muscle tone from poor conditioning with low activity level is prone to IUFP. The timing and strength of the muscle contractions is vital, hence the relative tone or laxity of the muscle controls or doesn’t , patella motion and the medial ligament stays locked around or “hung up” on the medial femoral condyle. An injury to the stifle, associated musculature or pelvis, combined with prolonged stall rest, may contribute to muscle atrophy and the development of IUFP. In very fit horses it has been noted that with one week of stall confinement, horse’s stifles may begin to lock. Muscle and neurological conditions such as spasticity, muscle spasm, myopathies, hypertoncity of the quadriceps, along with poor neuromotor coordination between flexors and extensors may cause IUFP. Abnormal tension of the patellar ligaments and abnormal conformation of the fibrocartitlage of the pateall or proximal medial trhochlear ridge can cause IUFP. Medial ligament pathology or desmitis may be the cause or effect of IUFP. Excessive training that places excessive stress on the joint such as in Standardbred racing in one direction on steeply banked tracks can cause excessive force on the stifle1. Abnormal hoof conformation consisting of long toe, low heels, and higher medial wall is also thought to contribute to IUFP. Other conditions common at the stifle joint such as: osteochondrosis dessicans, bone cyst, patellar fracture, cruciate ligament injury, congenital malformation of the medial condyle and or the patella, ligament sprain, degeneration of articular surfaces, or fracture, can be common found.

Until recently the conservative treatment for this condition involved unregulated exercise approaches with out specific prescriptive protocols or controlled progression. Many times the horse owner was told, “Work him in straight lines, and up and down hills”. This approach for

conditioning the horse was haphazard and not well defined. Therefore it was common for horses to become more problematically painful with prolonged stifle dysfunction, thus leading down the road towards injection or surgery. The above mentioned invasive approaches involve risk of infection, pain, swelling, and prolonged recovery time, without guarantee of successful return to function.

Physical therapy (PT) is a dynamic profession with an established theoretical and scientific base and widespread clinical applications in the restoration, maintenance, and promotion of optimal physical function8. Physical therapists diagnose and manage movement dysfunction and provide interventions to restore optimal physical function. Physical therapy on animals is

an emerging profession, representing qualified physical therapists that are using their physical therapy skills on animals7. Animals of all disciplines, whether working or domestic pets, get injured, undergo surgery, and have the potential to heal. The most common domestic mammals, dogs, cats, and horses, have similar connective tissue physiology to humans, therefore the same tissue healing principles that are commonly used in human PT can be applied to them.

The role of the newly emerging equine physical therapist is one of a trans- interdisciplinary approach. This would involve the PT working with other disciplines of veterinarian medicine, the horse owner, the trainer, the farrier, and other adjunct practitioners. The common goals of alleviating impairment, reducing disability and improving function are shared by all. Chiropractors, acupuncturist and massage therapist are all appropriate paraprofessionals to be involved in the recovery of injured animals. Many of these approaches can compliment one another in the ideal of total health, returning the equine to full recovery.

The prognosis of IUFP for return to athletic function is very good in horses that respond to rehabilitation exercise. However the problem may return if regular exercise ceases. After rehab intervention, persistent joint problems are very uncommon.  If there is no crepitis or obvious swelling noted, usually indicative of articular cartilage damage, prognosis is especially good.

In consideration that some horses are not prescribed proper rehabilitation treatment to address IUFP, or they may not respond favorably,  some horses my be appropriate for trial of sclerosing injections or surgery of the MPL. With the stifle joint of a horse’s hind limb being analogous to the human knee, it can be extrapolated that stifle surgeries may induce “reflex inhibition” of the quadriceps and surrounding muscles. Reflex inhibition of the human quadriceps occurs secondary to edema of the knee joint and joint capsule stretch receptor responses, therefore making the muscles unresponsive to the neuromuscular efferent message to “contract”, furthering the disuse atrophy. Cutting or fenestration of the medial patellar ligament of the horse of which sartorius, gracilis and the quadricep

muscles tendons attach, would certainly propose the possibility that reflex inhibition may follow and therefore could provide some delay of the horses return to optimal functional outcomes. PT intervention of modalities and motor relearning exercises are ideal for promoting a faster return of functional mobility after surgery of MLD or mild cases of UIFP. It is this author’s opinion that if a horse is to be stall rested after medial patellar desmotomy or fenestration, it would benefit from receiving the regiment outlined above, to improve the outcome and prevent reflex inhibition and muscle disuse atrophy commonly associated with post surgical prescribed stall rest.

All rights reserved by author Jennifer Brooks PT, MEd, CERP, Brookline, NH, Sept. 2007.

• Stifle Clinics: 2 hrs to 6 hrs.
• Core Conditioning Exercises for Riders: Functional Stabilization Program to strengthen your core, for balanced riding.
• Core Conditioning for Horse: Excellent easy exercises appropriate for conditioning your horse before seasonal riding or after lay up, colic surgery, or post partum.
• What does PT have to offer my horse?
• Rider Evaluations for prevention of back pain and physical dysfunction of your horse

Contact Jennifer at jenequinept@charter.net for availability and scheduling.