The skeleton of the Thoroughbred racehorse is uniquely adapted to balance both speed and strength. But the size and strength of these animals poses a challenge for fracture repair. Meticulous attention must be paid to the biomechanics at play if the athletic potential and at times the life of a horse is to be preserved. Fortunately, there are good surgical options for the most common racehorse fractures, often with favorable outcomes for return to racing.
The most common racehorse fractures are chip fractures in the fetlocks and knees. These occur at the front of the joints during extension of the limb at speed as the opposing bones in each joint contact one another with force. They may not cause overt lameness initially, but the exposed parent bone sheds debris into the joint, causing sustained inflammation and cartilage degeneration over time. Eventually, this is debilitating to the joint. However, prompt arthroscopic removal of fragments stops this process, and preserves the function of the joint. The prognosis is often excellent for a full athletic recovery.
Fractures of the third metacarpal condyle, or cannon, bone occur at the fetlock joint. Lateral (outside of the bone) condylar fractures are most common, typically involve only a relatively short portion of the bone, and are generally not unstable. These are best repaired with screws placed in the condyle to compress the fracture, speed bone healing and provide immediate comfort. On the other hand, medial (inside of the bone) condylar fractures tend to spiral far higher into the bone, and are at risk of becoming unstable. These fractures are best repaired with a plate spanning the entire length of the bone. In both cases, accurate reconstruction of the articular surface is paramount. This is aided by arthroscopic visualization during fracture reduction of unstable fractures. The prognosis for either type of fracture depends on the condition of the fetlock joint — a non-displaced fracture with no fragmentation at the joint surface generally has the best prognosis for athleticism.
The most common fracture of the first phalanx, or long pastern bone, is a vertically oriented fracture that begins in the central groove at the level of the fetlock joint. These can vary in length, but the best method of repair is to compress the fracture with screws. As always, attention to accurate reconstruction of the joint surface is important for post-operative athletic function. In some instances, these fractures propagate in multiple directions, resulting in numerous fragments that cannot be perfectly reconstructed. These cases are treated with a combination of screw placement and immobilization in a cast; pasture soundness is generally the goal.
Finally, major articular fractures can also occur in the knees. These are repaired using screws placed under arthroscopic guidance. Horses with minimal pre-existing degenerative changes (arthritis) in the joint have the best prognosis for athleticism, but even horses with severe changes that are intended to be retired to breeding can have their long-term comfort significantly improved by surgical fracture repair.