Managing osteoarthritis in the tarsus

Osteoarthritis of the distal tarsal (distal intertarsal and tarsometatarsal) joints is a common cause of lameness in horses. Different treatment options have been investigated and used in equine practice over the years.

Adequate hoof trimming and balance aiming to help to unload the medial aspect of the tarsus, with the use of wider, thicker outside branch or lateral extension to help unload the medial aspect of the tarsus have been recommended, especially for those horses with bowleg conformation.

Extracorporeal shockwave therapy has recognised analgesic effects and is often used over painful tarsal joints. Administration of NSAIDs is also common adjunct therapy in horses suffering from tarsal joint pain, but potential side effects of these drugs need to be considered.

Intraarticular injection with corticosteroids remains a main cornerstone when treating distal tarsal pain. As the joints involved are low motion joints, type of corticosteroid and their associated potential detrimental chondral effects are not of such a concern as when treating high motion joints.

Options for facilitated or accelerated ankylosis using chemical drugs have been used over the years. Chemical fusion agents include sodium monoiodoacetate (MIA) and, more recently, ethyl alcohol. MIA affect chondrocyte metabolism leading to chondrocyte death. MIA was associated with marked inflammatory response and pain and its use has therefore become less common. Ethyl alcohol has detrimental effects on the cartilage, which are expected to accelerate the process of ankylosis. Ethanol has also been associated with neurolytic effects, which leads to sensory innervation blockage at the intraarticular level. It is important to highlight that for any chemical fusion treatment approach, a pre-surgical contrast radiological study to assess the communication with proximal interatarsal/tarsocrural joints must be performed as diffusion of the chemical agent into these joints would cause severely detrimental effects. Laser can also be applied intra-articularly to produce ankylosis. These options of chemical fusion all have effects toward joint ankylosis, but the process to achieve to a sufficient ankylosis and pain-free sate may be prolonged and require repeated treatments.

Surgical approaches to distal tarsal joint pain from osteoarthritis include articular drilling and plate fixation. Articular drilling has been used for many years and the reported outcome is good. The produced causes destruction of the articular cartilage and subchondral bone with exposure of the subchondral bone allowing bone fusion to occur. The amount of cartilage damage is limited to the drilled tracts. A good amount of drilling is preferred to expedite he ankylosis process; however, excessive drilling or entering the plantar tarsal canal may cause instability and pain.

Most recently, arthrodesis with use of a trans-articular plate has been reported. A T plate is used and both affected joints are bridged. This procedure is more involved but produces a more stable, solid construct, which may decrease risk of pain and convalescence.