Many horses that exhibit hind-end weaknesses and/or lameness may be having pain associated with the hock. The hock is the large joint located between the stifle and fetlock. The hock receives a tremendous amount of the load during motion, providing propulsion along with the stifle. Therefore, this hard working joint is the most common site for rear limb stress, sometimes resulting in pain and performance limiting problems. Additionally, if a horse is reluctant to use his hock, because it's sore, over time other compensating structures, such as the back muscles and stifle can start to experience pain and weakness of their own. As one can see a horse with a hind-end weakness may have multiple problems. It is the veterinarian's job to try and help the horse by providing a diagnosis, which usually takes some considerable time to sort through, hopefully resulting in a plan to improve the horse's performance.
The most common hock disorder is distal tarsal osteoarthritis or "bone spavin". The hock consists of six bones and four joints. The lower (distal) two joints can develop inflammation, with ensuing degeneration of the cartilage and remodeling of the underlying bone. These distal two joints do not contribute much motion as compared to the large proximal (upper) hock joint, but they can be a significant source of pain when inflamed and arthritic.
Bone spavin usually results in chronic, intermittent lameness that worsens with increasing performance demands. Spavin may also be associated with less specific signs such as reduced performance, reluctance to work of the hind end, behavioral/training problems, and back pain. Affected horses will be most lame when they are first put to work, and tend to "warm out of it". Diagnosis is based on the history, appearance and conformation of the hock, lameness exam, and flexion tests, followed by radiographs. Complicated cases may require local blocks and sometimes more advanced imaging such as nuclear scintigraphy.
Treatment options for bone spavin include medical and surgical: Medical treatment encompasses a long list of options. Although an invasive surgical procedure intra-articular corticosteroids and corticosteroid hyaluronate (Legend and Legend like products) combinations are commonly used as an effective treatment, providing outstanding pain relief, typically lasting many months to a year or more. In some mild cases, exhibiting low-grade lameness, various less effective medical therapies are initiated. Anti-inflammatory such as "bute" can be used initially for short-term relief. Hyaluronate and glucosaminoglycans given as either injectable or oral products are commonly used for long term management of less severe cases. These products are also used prophylactically and adjunctively with joint injections for many performance horses. Other adjunctive therapies may include an exercise schedule, shoeing changes, acupuncture, chiropractic, shockwave, and magnet therapy.
Over years the two lower hock joints may naturally fuse, thus eliminating pain. Still natural fusion does not occur with many horses. In some cases where medical therapies do not seem to be helping, and fusion of the joint is not progressing, surgery may be indicated. Surgical fusion is normally only recommended for horses that are not responding to intra articular injection. In surgery the hocks will be "drilled", hock drilling removes the cartilage and promotes fusion of the joints. At times pins or plates are used to further facilitate fusion of the bones. Laser fusion is a new technique that is showing some positive results. Approximately 50% of horses will show improvement with drilling.
Bone spavin doesn't have to limit the abilities and performance of our top athletes or be career ending. Horse owners may be able to minimize the risk of osteoarthritis such as bone spavin by treating injuries promptly, and by modifying performance demands in horses in poor conformation. Young horses should be monitored for early signs of hock pain. Every horse's situation is different, working with your veterinarian to achieve the required care and medical attention can optimize the performance of your horse.