Diagnosing Stifle Disease

Diagnosis of stifle disease relies on a thorough history and clinical exam. Van Snow, DVM, from Santa Ynez, Calif., addressed stifle-related lameness at the Western Performance Horse Forum held in Nampa, Idaho, on Feb. 15-17.

Questions that are helpful to ask when diagnosing stifle lameness include the age of lameness onset and the circumstances surrounding it, including the contribution of deep footing, an exceptionally hard effort by the horse, or casting in his stall. Gait characteristics are sometimes typical for stifle lameness: The horse might have a low foot flight with limited limb flexion and a pronounced hip hike. Careful observation might show a characteristic "hang time" during the cranial (forward) phase of the stride, with the stride shortened. Lameness often is more evident when the affected limb is on the outside of the circle. The stifle-lame horse typically uses the limb in a very stiff fashion, and it is sometimes positive to upper limb flexion or extension tests (meaning the horse moves off sore after manual flexion or extension).

A veterinarian will do a careful hands-on examination of stifle structures, checking for thickening of patellar ligaments or the synovial lining and for joint effusion (excess fluid). Sometimes spurs and ridges can be felt.

Snow stressed that diagnostic anesthesia is an absolute requirement for diagnosis in all but the most blatant cases. Following confirmation of stifle involvement, imaging with radiographs and ultrasound are useful to determine problems in bone, ligaments, or meniscus. Nuclear scintigraphy has a poor correlation with diagnosis of stifle disease. In some locations, magnetic resonance imaging (MRI) is capable of imaging the stifle provided a horse's leg can be fully loaded into the machine. General anesthesia is required for MRI, but this form of imaging is invaluable when possible.

Frequently encountered diseases of the equine stifle include:

  • OCD (osteochondrosis dessicans with a cartilage flap or cyst);
  • Upward fixation or delayed release of the patella;
  • Meniscal disease;
  • Collateral ligament disease;
  • Osteoarthritis;
  • Patellar ligament disease; and
  • Patellar fractures.

Lameness associated with OCD of the medial femoral condyle is dependent on the integrity of the cartilage. If cartilage is intact, the horse has minimal or no lameness or joint effusion and is not responsive to limb flexion. But, disruption of cartilage produces lameness with significant joint effusion and a positive upper limb flexion test. In chronic cases, secondary joint disease is present 75% of the time.

Radiographing yearling stifles to look for flattening of the joint space or for an overt cyst was suggested so appropriate steps can be taken before the horse reaches two to three years of age, when only salvage efforts are possible with limited likelihood of achieving soundness. A veterinarian might counsel against future breeding of young horses with cysts since this problem is thought to be heritable, noted Snow. Older horses can develop cysts later in life due to trauma or due to impact loading on the joint. A cyst might have been present, but not communicate with the joint, until incurring trauma.

Interpretation of a stifle OCD seen on prepurchase exam depends on the age of the horse: A horse less than two years old might progress to lameness with training, but if seen in an older horse that has been through hard training, an OCD lesion might be an incidental finding.

Chris Ray, DVM, MS, Dipl. ACVS, of Weatherford, Texas, mentioned that a horse's age and use should be considered since some occupations require less hind end drive and thus might not place intense loading on the stifle, allowing for a continued successful career.

OCD lesions are often found in the femoropatellar joint, and these might self-correct in a young horse or remain for years without any clinical signs. Lameness is generally mild if present, but the horse can suddenly develop lameness and joint effusion, with hind limb flexion worsening the lameness. Radiographic exam, ultrasound, and MRI are effective imaging techniques for diagnosis.

Upward fixation of the patella or delayed patellar release is usually seen in horses less than three years old, especially those with straight hind limb conformation that are thin and under-muscled. This syndrome also occurs in fit horses given stall rest. Lameness and effusion can develop in chronic cases; radiographs are useful to evaluate the joint.

Injury to the middle patellar ligament is often a consequence of cutting the medial patellar ligament to address upward fixation. The trouble that usually develops in the middle segment of the ligament is best visualized with ultrasound.

Meniscal injuries include linear tears or generalized loss of integrity, which are found in 10% of all stifle lameness cases. Usually there is stifle effusion and a positive response to limb flexion in addition to overt lameness. Arthroscopy is the diagnostic strategy of choice for full assessment, although MRI offers an alternative as it becomes more available.

Collateral ligament injury, especially of the medial collateral ligament, also occurs with damage of the medial meniscus. Lameness tends to be progressive over several months. Diagnostic ultrasound is the best tool to identify this problem.

Although uncommon, a patellar fracture and associated soft tissue injury can result from trauma, with the horse being very lame, walking on the toe, and maintaining the upper leg in a flexed position. Radiographs identify the fracture.

Osteoarthritis due to articular cartilage trauma often has no obvious abnormalities seen on radiographs or ultrasound, so arthroscopic surgery is the best option to use to prognosticate damage and enable therapy.

For more from the Western Performance Horse Forum click here.

About the Author

Nancy S. Loving, DVM

Nancy S. Loving, DVM, owns Loving Equine Clinic in Boulder, Colorado, and has a special interest in managing the care of sport horses. Her book, All Horse Systems Go, is a comprehensive veterinary care and conditioning resource in full color that covers all facets of horse care. She has also authored the books Go the Distance as a resource for endurance horse owners, Conformation and Performance, and First Aid for Horse and Rider in addition to many veterinary articles for both horse owner and professional audiences.

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