Reverie on the Radial Nerve

In our first week of medical school (more than 10 years ago), one of the earliest anatomy lessons was for us to memorize the roots and branches of the brachial plexus.

In our first week of medical school (more than 10 years ago), one of the earliest anatomy lessons was for us to memorize the roots and branches of the brachial plexus. (The nerves exit the spinal cord at the neck, coalesce into a web and gather into new configurations that become the nerves that travel down the arm to supply muscles, for movement, and skin, for sensation.) It's complex. I, with my classmates, learned it by rote, passed the exam, and honestly, haven't thought about it much since then. My colleagues who chose hand and upper-limb surgery are intimately involved with the radial nerve. The neurologists, I'm sure can trace out the branches. For me, as a generalist, I usually only need a passing knowledge. Is this injured patient neurologically intact? Almost always, the answer is yes (but I always check).

Wow, now I have a new appreciation for the radial nerve and its vulnerability. We have quite a few patients with radial nerve palsies (ie. injuries), so now I am quite used to identifying the syndrome: drop-hand, with difficulty extending the fingers and wrist, and difficulty with supination (turning palm up).

What's interesting is the various levels of injury that have occurred. The most common is a radial nerve injury where it passes through the spiral groove of the humerus: often with a midshaft humeral fracture. One of our patients doesn't have a humerus fracture, but you can see the scar on the medial aspect of her left upper arm where she had a laceration, exactly in the crucial spot. Sadly, her right hand is also badly crushed; I hope she will again use her right thumb and index finger, perhaps the middle finger, also.

Another patient was a man who, during the earthquake, was trapped in an awkward position trying to protect the baby cradled in his arms. Tragically, the baby perished, as did his wife and older child. He had a right drop-foot (peroneal nerve palsy from compression at the fibular head) and a left drop-hand, with a scar on the back of his wrist. He told us it had been a deep laceration that had since healed over. So, thinking that it had also cut his extensor tendons (of wrist and fingers), they did some exploratory surgery to look for the ends, in order to sew them back together. So many weeks after the accident, the ends risked being difficult to find since they can retract considerably. I joked to the surgeons that the tendons might be in Miami by now.

The extensor tendons, though, were still firmly in Haiti, intact. His problem was neurologic: a radial nerve palsy, possibly compressed in the forearm or elbow when he was trapped. "Maxine" is a little girl, nine years old, with round cheeks and a toothy grin. She had a compartment syndrome of the right forearm (as "Bobby" did of the leg). Her fingers are curled up in full flexion. We put her in a volar (palm-side) splint to prevent contracture at the wrist. There is no movement there at all. She is very tight in the elbow, too. I assume that her radial nerve injury occurred because of the increased pressure in the forearm; the elbow stiffness might just be from prolonged immobilization. The other possibility is that she has a concurrent injury more proximally, before the nerve branches to the triceps. The principle of neurology is always: where is the lesion, what is the lesion, which sounds easy but is (I think) difficult.

And there are others. One patient reportedly had some concrete fall on her shoulder, with axillary nerve dysfunction: my theory is that it pulled at the nerve roots coming from the vertebrae in the neck. Another of our patients, who is very depressed, had a shoulder dislocation for six weeks, which is now in the right position but with a very loose joint capsule. She also has an associated radial nerve palsy, probably at the level of the brachial plexus.

The good news is that the prognosis is fairly good. Peripheral nerves (as opposed to spinal cord) can repair themselves as long as the nerve sheath is intact to guide the way. Already, you can see the beginning of some wrist extension where before the hand flopped uselessly. Physiotherapy will help. And time is a great panacea. Nerve grows slowly - something like a millimetre a day - but it does grow.