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Degenerative joint disease, or arthritis, is a common and debilitating condition in the horse which causes lameness and loss of performance.  Usually there is an underlying cause – such as a traumatic injury to the joint, but regardless of the cause once degeneration of the joint begins the progression and clinical signs are similar.

When dealing with joint injuries, the aim should always be to provide effective treatment before the joint begins to degenerate. However, this is not always possible, and in the minority of cases the joint becomes so severely affected with degenerative changes that lameness becomes debilitating, regardless of what treatments are administered to the joint

In the scenario described above, arthrodesis – or ‘fusion’ – of the affected joint can be an effective means of providing pain relief. Depending on the joint involved, the horse may also be able to return to work after arthrodesis – but this is only the case with joints that normally have limited movement. Examples include the small joints in the hock, and the pastern (proximal interphalangeal) joint.

With the small joints in the hock, there is such limited movement that arthrodesis can be achieved by simply removing any remaining cartilage from the joint surfaces – performed by drilling across the affected joint. The body then forms bridges of bone across the joint at the drill tracts, fusing the joint. This takes time to occur, and typically horses will take 6 months or more to come sound after surgery.

With the pastern joint, although this is still considered a ‘low motion’ joint, there is substantially more movement than seen in the small hock joints. Because of this, simply removing the remaining cartilage does not enable fusion to occur. Instead, this needs to be combined with surgical placement of screws and plates to bridge and immobilise the joint. Once this has been performed, fusion will occur gradually over about 6 months after surgery.

The outcome following surgery can be good, with around three-quarters of horses being able to return to work. This varies a bit however, depending on which joint is involved and the severity of initial injury.