For the horse who competes in dressage, where hind-end engagement is a key to correct performance at all levels of competition, hock pain is a common and marked impediment. The significance, treatment and prognosis depend on the source of the pain. Although prescreening can help identify some potential problems, no system is foolproof. Similar to the prevention of many sources of lameness, a conscientious system of horse development in the care, feeding and training is the best method of prevention and control.
The hock consists of 10 bones and four joints and is supported by several ligaments. The tibiotarsal joint is a ball-and-socket joint that has the largest range of motion. The other three joints are low-motion joints and serve as good shock absorbers. When the tibiotarsal (or tarsocrural) upper joint is inflamed, there is an increase in synovial fluid. The old-time horseman term for this is “bog spavin.” This is a vital joint for a performance horse, and swelling is often a sign of a problem. If that is something you notice, you should call your veterinarian to help you garner more information and provide you with treatment options.
The tibiotarsal joint is also a joint where osteochondritis dissecans (OCD) is commonly found. OCD is a developmental problem that affects joint cartilage and often affects the bone just beneath the cartilage. Normally, OCD is a condition that is identified in the young horse. The worst lesions are found early. These OCD lesions can be present without any lameness issues; however, when they are present and there is filling in the hock, surgical removal is the treatment of choice. Fragments of bone and/or abnormal cartilage can break loose and result in joint inflammation, and even if this has not caused issues in the past, it is wise to remove them from the high-end performance horse as they may eventually break loose with poor timing. Once they do break loose, resulting in inflammation, some people opt to put a band-aid on the issue by injecting the joint with corticosteroids or by using nonsteroidal anti-inflammatory products. However, this actually risks further damage to the joint.
In the case of a horse who is lame due to an unknown cause, joint distension or enlargement, is usually indicative of a problem. It can be helpful for a veterinarian to use local anesthesia in the tibiotarsal joint to confirm the source of lameness before more in-depth surgery. Nothing is more discouraging than having a surgery done with rehabilitation time only to discover the lameness came from elsewhere. In the absence of lameness or any sign of a radiographic lesion with a full component of radiographs, the joint can be drained and injected with a veterinarian’s choice of product and with a period of rest prescribed. It is not uncommon for some level of filling to return. The tibiotarsal joint frequently communicates with the next joint down, the proximal inter-tarsal (PIT) joint. The PIT joint is a less common source of lameness.
The most common sources of hock lameness in horses are the bottom two joints, the distal intertarsal (DIT) and the tarsometatarsal (TMT). These two joints have very little effect on the movement of the hock unless they are painful. If that is the case, the horse is very guarded in the movement of the hock. Usually, the lameness is most evident when he is under saddle and being asked to work. The horse with osteoarthritis of the lower joints may carry that hip higher during the swing and landing phase of the stride. Often he will leave the leg further behind when it is on the outside of a circle and have a markedly shortened anterior stride. These horses are usually quite positive to an upper-leg flexion test. Occasionally, pressure on the inside of the hock will be painful. Radiographic evidence of arthritis can be there in the absence of lameness, and lameness can be there in the absence of radiographic evidence. Some horses are perfectly normal on flexion.
There are many avenues of treatment for arthritis of the lower two hock joints. These include systemic anti-inflammatory drugs, intra-articular injection of the joints, systemic products that are considered to protect cartilage, magnetic therapy, shockwave therapy or laser therapy. Usually two or three of these treatments are used in combination.
It is important that you address hock pain in your dressage horse. A change of movement as a result of hind-leg pain threatens both his other hind leg as well as his front legs. There are a variety of conclusions regarding the prognosis for a horse with hock pain. It has been my experience that, as long as there is no extensive radiographic change, hock pain stemming from the lower two joints can be controlled and can resolve. However, the greatest successes have been in cases where training has been appropriately modified or ancillary therapies such as magnetic hock boots are used.
Some veterinarians, including myself, believe that frequent cortico-steroid injections of the tibiotarsal joint (three to five times a year) are partly responsible for tears at the origin of the high suspensory ligament. Some of the origin is included in the TMT joint. Micro-tears in the high suspensory occur regularly and heal regularly. When this area is frequently treated with a corticosteroid, the healing process is interrupted. There is not room in this article to address high-suspensory tears, but they can appear very similar to arthritis of the lower two hock joints.
How do you choose a young horse intended for dressage from the point of view of avoiding hock pain? There is some evidence that horses who are base-wide behind (where the hind fetlocks and feet point out marginally) are better able to engage for upper-level work. You must not confuse this with cow hocks that are actually predisposed to hock problems. There is evidence that a horse with a straighter hock angle has more longevity, so a sickle-hocked conformation is not ideal.
I consider radiographs to be an important tool in assessing the young horse. OCD lesions can be there in the absence of clinical signs and stalemate you later. There can also be radiographic signs that the lower hock bones did not ossify thoroughly and show signs of having been crushed in babyhood. Although horses with this problem are usually sickle-hocked, that is not always the case.
A practice of a long warm-up—about 15 minutes of walking—is always appropriate. Dressage is a system of progressive strength training, and of a day or two per week of rest or light work is needed to allow for healing. Ensuring that your horse has the strength to do the exercise being asked and is not asked to do it when he is too tired is the best protection for both joints and soft tissue.
Mary H. Bell, VMD, is the chair of the Equine Canada Health and Welfare Committee. She is past chair of EC Medication Control Committee and co-chair of the CFIA/EC initiative to develop a national equine biosecurity standard. She is also a licensed FEI Veterinary Delegate for dressage and jumpers and an FEI treating veterinarian. Based in Puslinch, Ontario, Canada, she operates Mannington Equine Services. (manningtonequine.ca.)