Examining The Irish: Humerus Fractures

This is a quick follow-up to Eric’s post of April 3rd regarding Nick Watkins' arm injury.  It has already been reported that the sophomore corner should be ready to go for summer workouts, so I will not go into depth on his specific prognosis.

The humerus is the bone of the upper arm. Its head contributes the ball to the ball-and-socket joint of the shoulder. Distally, it forms the elbow joint with the radius and ulna.

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In most cases, a humerus fracture is treated with a cast in an out-patient setting. In other cases, surgery is indicated when the fractured pieces cannot be realigned manually. A consideration here is muscle mass. Muscles perform their function by pulling on bones. When the bone is intact, the muscle moves the whole bone through a given plane of movement. Muscles, however, are not attached along the entire length of the bone. Instead, they attach at discrete points called insertions. If the bone is broken, the force that a muscle exerts at that discrete point would not translate beyond the site of the fracture. In this case, the muscle would pull one fractured piece farther away from proper alignment. I suspect that in athletes, due to increased muscle mass, surgery would be indicated and that surgery would decrease the healing time by creating greater stabilization.

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Red line = location of fracture. Black arrow = pull of pectoralis major muscle. Blue arrow = movement of proximal fragment. Green arrow = movement of distal fragment . As we can see, the muscles can pull the bones out of proper alignment by their normal action.

Let’s turn now to some complications of humerus fractures. These complications are rare, but due to potentially serious outcomes, they are worth mentioning. The first is avascular necrosis. Breaking down the words is instructive. Avascular – no blood vessels, or loss thereof. Necrosis – pathological cell death. Avascular necrosis can occur when the head of the humerus, the ball in the shoulder joint, is fractured at its narrowest point. Small, delicate blood vessels pass through this point and are susceptible to damage. Bone is just as much a living tissue as the heart and the kidneys are. When the blood supply is lost, the living cells are deprived of oxygen and nutrients. Toxic waste products build up, and the cells suffer damage beyond their ability to repair. In short, the ball in the ball-and-socket joint dies and degenerates.

Trauma to the shoulder can cause the type of fracture that leads to avascular necrosis. So to keep everything straight: the humerus is an arm bone that contributes to the shoulder joint. If an athlete sustains trauma to the shoulder, among other things, he can break his arm. To prevent avascular necrosis from occurring, fractures of the humeral head are treated by orthopedic specialists with surgery so that the blood supply is not compromised.

A second rare complication of humerus fractures is nerve damage. Two large nerves, the radial and the median nerves, course through the upper arm to their targets in the forearm. At certain points along their path, they run deeply, along the surface of the humerus. Because bone and nerve are so close at these points, traumatic fracture of the bone can cause traumatic damage to the nerves. If the fracture occurs at the mid-shaft of the humerus, the radial nerve is more likely to be damaged. This would lead to a decreased ability to extend the fingers and the wrist. If the fracture occurs just above the elbow, the median nerve is more likely damaged. This would lead to a decreased ability to flex the fingers and the wrist. Finally, if the fracture occurs on the inner aspect of the yellow, the ulnar nerve, another nerve running from the shoulder to the hand, can be affected. This would result in some strength and sensory problems over the fourth and fifth digits.

Palica

Green line = humeral head fracture (avascular necrosis). Red line = mid-shaft fracture (radial nerve damage). Black line = supracondylar fracture (median nerve damage). Blue line = medial epicondyle fracture (ulnar nerve damage)

These are a few of the complications that can arise from humerus fractures.  I do not see any reason to doubt the timeline provided by the team for Watkins' recovery, and he should be ready to go by fall camp. Stay tuned for a future post regarding nerve damage after traumatic injury, which will be examined in light of Jaylon Smith's preparation for the NFL.