The hock, or tarsus, is a complex collection of joints in the horse. Identifying lameness in one or more of those joints, and treating the problem, can be challenging. However, Alberto Serena, DMV, MRCVS, of Auburn University, and colleagues have found that injecting medication into one joint can treat an adjacent joint as well.

This study demonstrated that when 80 mg of methylprednisolone acetate (MPA) is injected into the tarso-metatarsal (TMT) joint, a therapeutic concentration of its ester, methylprednisolone (MP), will diffuse into the distal intertarsal (DIT) joint. These are the two lower hock joints that often develop osteoarthritis.

There were actually two phases of the study; in the first, MPA was injected into one TMT joint in each of seven sound horses. Serena reported that the concentration of MP in the DIT joint was highest six hours after injection of the TMT joint, but it was evident after one-half hour and dropped off quickly to zero concentration by 12 hours.

In the second phase, nine horses received injections of MPA into the left TMT, with MP measured in all DIT joints at 6 hours