This is a relatively common fracture in race horses. it is thought to occur from recurrent "micro-damage" during training that finally gives way. It is a longitudinal crack down the lower end of the cannon bone, splitting the cannon bone into the fetlock joint surface. In flat racing horses, the crack usually occurs on the left forelimb, on the outside (lateral) side of the bone. The fracture also occurs in Standardbred racehorses and in those horses also commonly occurs on a hind limb. The term for a fracture involving the joint surface is "articular". Articular fractures cause an added problem- they damage the joint surface, resulting in arthritis.

The injury usually results in very severe lameness but occasionally causes less severe lameness. In addition, there is usually swelling of the lower limb and fluid filling of the fetlock joint.

Occasionally, non-displaced fractures can be a surprising diagnostic challenge to a veterinarian. Care must be taken by the veterinarian in using nerve blocks if this condition is suspected, because if the horse loses sensation in the lower limb, they could overload the non-displaced fracture and make it worse.

DIAGNOSIS is usually clear from radiography; a large and highly visible split into the fetlock joint. However, the changes in some radiographs are more subtle.

TREATMENT: In most cases, the recommended treatment is surgical fixation by screws. The key to successful treatment of this fracture is establishing perfect alignment of the joint surface. If there is poor alignment, arthritis will develop and cause permanent and severe lameness.