Accessory nerve is key to extent of Davis' injury 2 possibilities seen for muscle weakness

April 30, 1991|By Mary Knudson

What happened to sideline Baltimore Orioles first baseman Glenn Davis, and how long will he be out?

For the doctor who diagnosed Davis' injury, the first question is much easier to answer than the second.

After Davis saw Dr. James N. Campbell, a professor of neurosurgery at Johns Hopkins Hospital, the Orioles announced that Campbell diagnosed an injury to the spinal accessory nerve in Davis' neck, causing wasting and weakness to a major muscle in his right shoulder.

Yesterday, Campbell declined to reveal his findings about Davis, but he did explain this type of injury and how it is fixed.

Unless it is a "fluke" -- something that clears up by itself -- the usual treatment is surgery, and recuperation may be anywhere from "very short," which would mean a return this season, or "much longer," which would put Davis out for 1991.

Davis was in New York yesterday seeing three specialists and may see others before he and the Orioles announce his plans. But if the Hopkins diagnosis stands, this is what's going on:

Although this nerve injury is rare, ballplayers constantly are developing muscles that may predispose them to the injury, Campbell said.

The accessory nerve begins at the base of the neck in the junction of the lower brain stem and the upper spinal cord. The nerve sends messages for movement to a head-turning muscle called the sterno-cleidomastoid that runs down the side of the neck and to the trapezius muscle, involved in moving the right shoulder and lifting the right arm, Campbell said.

When the nerve is damaged but there is no known direct trauma, the nerve either may have become stretched from overuse of the arm or it may become "entrapped by fibrous tissue bands" that build up around it, Campbell said. The latter problem is similar to carpal tunnel syndrome, in which the median nerve in the wrist is entrapped, often from repetitive movement.

There is little medical literature about this type of nerve injury, said Campbell, who is a co-author of one of the handful of articles published. So, there is not much known about specific causes of this injury when there is no direct trauma and the pain develops gradually. Shoulder pain can result from both the injured nerve and strain on other shoulder muscles compensating for atrophied muscle, Campbell said.

Diagnosis of the nerve damage involves physical examination and nerve conduction studies and electromyograms in which a needle records electrical activity in muscles, Campbell said. These electrical tests tell the examining doctor if the muscle is working normally or is atrophied.

"It's detective work, really, in figuring out where the lesion [injury] is," Campbell said. "If muscle A and B are functioning normally, it must be at the point where the branch to muscle C is that the injury occurred."

So, once the diagnosis is made, what happens next?

When the problem is nerve entrapment, "the pain can get worse as entrapment gets worse," Campbell said. "It's unlikely to get better" just by rest.

If the pain is due to repetitive stretching of the nerve from muscle overuse, the pain would clear up with rest. But, start to use the muscle again, and the pain returns.

The likely treatment involves surgery, Campbell said. For example, "If a nerve is stretched to the point that it's pulled apart, it could be operated on and surgically repaired," he said.

If the nerve is stretched, but not to the breaking point, then the doctor tries to locate the source of the problem and surgically "make that go away" so that the nerve then recovers.

And when the nerve is entrapped, the bands of fibrous tissue are cut to free it.

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