The tarsus, or hock, is unique because it contains both high and low motion joints, all of which can undergo disease and cause hock lameness. There are many types of pathologic processes that can lead to disease including acute injuries, fractures, developmental disease (osteochondrosis), and soft tissue injuries. However, synovitis/ capsulitis and osteoarthritis (OA) of the hocks is frustratingly common in all horses of any discipline, and especially in sport horses and performance horses, often necessitating repeated and ongoing treatments.

Horses with lameness in the distal (low motion) joints of the hock (the tarso-metatarsal or ‘TMT’-joint, and the distal intertarsal or ‘DIT’ joint) typically demonstrate varying degrees of lameness. They have a shortened stride and the lameness is worse with the affected limb on the inside of a circle. Riders often report the horse has a reluctance to work ‘under them’ or ‘through’ from the side with the worst affected limb.

The lameness can often be exacerbated by a full-limb flexion test and occasionally you can even elicit a direct pain response by pressing firmly on the medial (inside) of the tarsal joints themselves. Intraarticular analgesia though is the most accurate means of confirming a diagnosis of hock lameness and is a relatively easy procedure, in most cases, when performed by an experienced veterinarian. It is important also to differentiate pain in the distal hock joints from pain associated with the proximal suspensory ligament. This may require the use of other diagnostic tools like ultrasound or scintigraphy. As said above, synovitis/ capsulitis of the DIT and TMT joints is relatively common in all athletic horses and it is important to note that there is often a poor correlation between lameness and any radiographic signs of disease. Osteoarthritis of the DIT and TMT joints is also common and can vary from mild to severe. In severe cases the joint space narrowing can be significant with associated subchondral bone sclerosis and lysis. Horses with severe lesions are typically very lame and response to treatment limited so the purpose of treatment of hock lameness should be to slow or limit the progression of the disease. Some veterinarians advocate surgical or medical fusion of the lower hock joints in those severe cases. However, the benefits of these techniques have been questioned under certain jurisdictions due to the ethical and welfare considerations for the horse.

Arthramid® Vet has been used to successfully treat hock lameness in horses and offers veterinarians and owners a safe and effective long lasting treatment option. In a recent case series report from 3 veterinary centres in the UK (pending publication) a total of 497 hock joints (295 TMT/ 202 DIT) were treated with 0.5ml or 1.0ml 2.5% PAAG (Arthramid® Vet). The majority (88.9%) of joints treated were sound within 2 months and most (approximately 61%) remained in work for more than 2 years after treatment. A minority (approximately 35%) did receive additional treatment with either a further treatment of 2.5% PAAG or other medications (corticosteroids, hyaluronic acid or IRAP) during that time period.

These results would indicate that overall, treatment of hock lameness in horses with synovitis or OA of the TMT and DIT joints can be rewarding with 2.5% PAAG. The challenge is developing an effective management plan around the horses performance schedule and the owner’s desire to rehabilitate the horse. Integration of the gel into the joint takes 2 to 4 weeks to occur so early treatment intervention offers a practical solution for the owner and veterinarian, with the addition of conventional or subsequent treatments, if required, whilst the horse remains in a competitive environment. 2.5% PAAG Arthramid Vet is long lasting, effective and carries no competition with-hold times making it well worth considering in the treatment and management plan for horses with hock lameness.

Dr Jason Lowe, Veterinarian.