Diagnosis and Treatment of Hock Lameness

Cutting horses serve as a perfect model for the discussion of hock lameness, noting that no other discipline places more stress and torque on the hocks than what these horses experience, said Jerry Black, DVM, of Pioneer Equine Hospital in Oakdale, Calif., at the AAEP Focus meeting in Ft. Collins, Colo., on July 31.

Inflammation of the lower rows of hock joints is referred to as distal tarsitis, and it is associated with a variety of clinical signs. According to Black, an affected horse might demonstrate a "stiff" gait, especially noticeable when offloaded from a horse trailer. The horse tends to improve with warm up, yet a cutting horse in work might be reluctant to stop or properly hold the stop. There is a premature release of the caudal (toward the tail) phase of the stride in a horse with distal tarsitis (hock inflamation), resulting in a shortened cranial phase of the stride. This occurs as the horse feels shearing forces in the affected joints as he starts the push phase of the stride. Pain causes him to quickly release forward movement of the limb, resulting in a "stabbing" gait. Usually trotting the horse in circles will amplify the degree of lameness.

There are many causes of distal hock tarsitis, including incomplete or delayed ossification (mineralization) of the ends of the long bones of the joints, with concurrent osteochondrosis. Black feels there is a genetic influence; this is based on his findings of significant radiographic changes visible in 55% of 25 yearlings of the same cutting horse bloodline.

Other causes of tarsitis are related to traumatic injury from occupational use or due to degenerative problems that lead to osteoarthritis. Black says other factors can lead to distal hock disease, such as structural tendencies toward sickle hocks, cow hocks, and/or post-legged conformation.

Black urges the practitioner to perform a very thorough clinical exam that includes observation of the horse in a straight line trot, thorough palpation of the entire leg as well as the thoracolumbar region of the back, and flexion tests. It is important to do a hoof tester exam to identify or rule out any hoof problems. In addition to gait evaluation on the longe line or freely in the round pen, the horse might need to be ridden under saddle. All exams should be conducted on good footing.

Black stressed that a full radiographic series is important in tarsal evaluation. He notes that osteoarthritis typically starts in the distal intertarsal joint, with the tarsometatarsal joint affected next, and eventually osteoarthritis will advance into the proximal intertarsal joint due to biomechanical forces imposed on that joint. Other imaging techniques, such as ultrasound, nuclear scintigraphy, CT, and MRI, are valuable to define the extent of the lesions.

Black explained that treatment depends on the severity of the lameness and the level of pain. It also depends on radiographic findings, the age of the horse, its use, and the time of year the problem is being addressed.

Treatment goals focus on alleviating pain with effective and long-term results to protect the health of the joint while also allowing the horse to perform its intended use. The gold standard of treatment still relies on IA injection--it is efficacious and cost- effective. Use of systemic joint therapy is most useful when administered as a series of IV hyaluronic acid or intramuscular PSGAGs (Adequan), or as a combination. Black notes that while many sport horses cannot compete with non-steroidal anti-inflammatories in their systems, Western performance horses can, with these medications useful in managing tarsitis.

For horses that don't respond well to conventional IA anti-inflammatory treatment, IRAP therapy is effective in quickly decreasing inflammation. Shock wave therapy has been used with good results on tarsitis.

Therapeutic shoeing is essential to remove excess toe at the dorsal hoof wall and/or sole, and to provide adequate heel support with extended branches of the shoe and/or a wedged bar pad. The shoe should be square-toed or deeply rockered to ease hoof breakover. In addition, management and training changes must be implemented for treatment success: The horse should be given increased free-choice exercise, longer warm-ups, and when possible, training in deep surfaces and overtraining should be avoided.

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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