The humerus is the upper arm bone that joins the elbow joint to the shoulder joint. Rarely it can be fractured. The injury is more common in foals, weanlings and yearlings and usually results from trauma, most commonly a fall. I have seen this injury in several young horses that fall down during attempted halter-breaking. In adults, it can occur from a fall or from a kick by a pasture mate.

A different syndrome of stress fracture of the humerus can occur in racing Thoroughbreds.

Diagnosis usually requires x-ray of the upper arm. This can be difficult with small portable x-ray units and a large horse because of the heavy musculature of the upper arm. Ultrasound is also very useful in these cases. Nuclear scintigraphy can be diagnostic for stress fracture.

Treatment ranges from conservative (standing in a stall until the fracture heals) to a variety of surgical repairs. The treatment options depend on the particular nature of the fracture.