The radius is the bone between the carpus (a/k/a knee) and elbow. The tibia is the long bone between the hock and stifle in the rear limb. They are bones of similar design, so they are discussed together here.

A hairline non-displaced fracture of the radius or tibia may cause severe lameness. These fractures usually result from a kick, but can happen with certain types of overload as well.

Horses with hairline fractures must be confined for 8 weeks until the fracture is healed.

Diagnosis can be surprisingly difficult in some cases. These types of fractures may be missed on radiograph. In these cases, horses are returned to work or turned out and then suffer a complete and fatal fracture.

Fracture of these bones can also occur as full blown loss of the structure from severe trauma. In most cases, this injury is caused by a kick to the inside surface of the limb where there is almost no muscle covering over the bone.

In this case, the horse cannot bear any weight on the limb and the limb may hang limply and be moveable in all the wrong directions. In many cases, crunching of bone can be felt with movement, and there is often severe swelling. In some cases, the fracture is compound, with bone protruding through the skin.