Of all of the long bone fractures (humerus, femur, radius, ulna and tibia), humeral fractures are the least common.
Motor vehicle trauma is the most frequent cause of humeral fractures in cats. These injured animals tend to be young, non-neutered males who roam away from home and get hit by a car. Animals of both sexes and of any age are susceptible to this type of trauma if not kept restrained. Cats can develop non-traumatic fractures of the humerus when certain disease conditions exist. These fractures, also known as "pathologic fractures," can occur if the animal is malnourished, has a systemic illness such as kidney disease, has an endocrine disorder such as hyperparathyroidism, has a bone infection (osteomyelitis), or has cancer of the bone.
Immature bones have growth plates (physes) that are still "open" and growing. These regions of the young bone are generally weaker than the bone that has already been created. The energy of a trauma often results in fracture at these parts of the immature bone and can lead to premature "closure" of the physes resulting in abnormal growth of either end of the humerus. Frequently encountered fractures of the immature femur include physeal fracture at the end of the bone near the shoulder joint, fracture of the part of the humerus that forms the elbow joint, and fractures of the middle of the bone.
Mature bones have more uniform strength along their entire length and the energy of each particular trauma may lead to fractures in various portions of the bone. Frequently encountered fractures of the mature humerus include shaft fractures and joint fractures involving the elbow.
A very common injury to the humerus is fracture of the lateral condyle as the animal jumps down from a height. In this fracture, the end of the humerus splits in the middle disrupting the smooth contour of the inside of the elbow joint. The surface of the elbow must be surgically reconstructed or the animal will suffer severe arthritis in the future.
Fractures of the midshaft (diaphysis) of the humerus can be classified as "open" or "closed" depending on whether the skin surface has been damaged during the injury. Open fractures have a greater chance of getting infected may have more complications than closed fractures.
As with all fractures, fractures of the humerus can also be classified as "simple," if the bone breaks into two pieces, or "comminuted," if there are multiple pieces.
Each case of humeral fracture needs to be evaluated in its entirety (age of animal, severity of the fracture, experience of the surgeon, and financial concerns of the owner) to determine the most appropriate and best form of treatment.
Inappropriate case management, inadequate surgical stabilization, or poor aftercare can lead to complications such as non-unions (fractures that will not heal), malunions (fractures that heal in an abnormal direction or orientation), osteomyelitis (bone infection), arthritis of the shoulder or elbow, or a non-functional leg.