So here’s the scenario. It’s Saturday night and I’ve had a long week. I hit the bars and tip back one or two too many. Stumbling out of the last bar, I find I can’t make it past the city park without landing on my nose, so I plop onto a park bench. Slinging an arm over the back of the bench to stabilize myself, I fall into a deep slumber.

Now it’s Sunday morning and the sun is shining, the birds are singing and I’ve got a splitting headache. My arm is where I left it last night, slung over the back of the bench. I haul it back in front of me, but something is wrong. When I try to extend (cock up) my wrist, it doesn’t go anywhere. In fact, it droops downward. Moreover, I can’t straighten my drooping fingers, either.

As I investigate further, I find that the skin on the back of my hand is numb. What gives?

The problem is that I have injured the arm’s radial nerve. As a result, the muscles it controls and the skin-sensation it manages are out of commission. On its course from the spinal cord in the neck to the forearm and hand, the radial nerve–a bundle containing many individual nerve-fibers–spirals around the humerus-bone of the upper arm. The nerve is particularly vulnerable to injury near the mid-portion of the humerus, in this case by allowing the hard edge of the park-bench to compress it against the bone all night. The weakness produced by this condition is usually more impairing than the numbness that is also present.

With “palsy” as another word for weakness, this kind of injury to the radial nerve is called “Saturday night palsy.”

Of course, injury to the radial nerve injury can occur on any other night of the week, as well, and the setting does not have to be a park-bench. The usual common denominators are that alcohol or other drugs are involved, and because of the deep, drug-induced slumber, the arm is kept in the same position all night long.

This part of the radial nerve can also be injured by off-course injection-needles intended for the shoulder muscle above it (the deltoid muscle).

When this occurs, the pattern of weakness and numbness is the same, but instead of going by the name of “Saturday night palsy,” the nerve-injury is sometimes called “law suit.”

In either case, the nerve and its functions usually recover over a time-frame that can vary from days to longer than a year. The faster recoveries mean that the nerve-fibers within the nerve-bundle were sick but not dead. In more severe injuries, the nerve-fibers at the site of the injury and beyond have actually died, and their surviving stumps need to send out sprouts to replace the missing parts. This is a slow process. The growing sprouts reach the upper forearm (where the wrist-straightening muscles are located) before reaching the mid-forearm (where the finger-straightening muscles are located). As a result, the muscles that straighten the wrist usually recover before those that straighten the fingers.

People with Saturday night palsy often exercise their arms by squeezing rubber balls or similar objects. Unfortunately, this activity exercises the wrong muscles.

The radial nerve and its muscles have nothing to do with flexing the hand muscles. These functions are instead served by the arm’s median and ulnar nerves which were not injured in the first place. In order to be useful, an exercise would need to focus on cocking up the wrist and straightening the fingers.

But this, too, might be futile because the paralyzed muscles have no incoming nerve-messages to activate them. Until the damaged nerve-fibers reconnect with the muscle-fibers, the most useful exercise is a passive one in which the other hand does the work by stretching out the weak muscles at least daily. Using passive “range-of-motion” exercises, people with nerve-injury can avoid shortening of tendons and freezing of joints that might otherwise occur as complications while waiting for the nerve to recover.

What else can be done? Unfortunately, there is a dearth of scientific evidence in the form of randomized, controlled trials–the gold-standard for judging a treatment–to go by. All we have to go on is collective “clinical experience” and common sense. In order to properly heal and grow, nerve-fibers need a good supply of nutrients, so healthy eating–perhaps supplemented by a multiple vitamin or two each day–can give the nerve the building-blocks it needs to properly recover. Avoidance of alcohol might prevent a second injury. Because alcohol can also produce a direct toxic effect on the body’s peripheral nerves, abstinence would additionally prevent this barrier to recovery.

In cases of prolonged weakness, electrical stimulation of the affected muscles via probes applied to the skin might keep the muscle-tissue healthier until they can receive more normal activation through their nerves.

While waiting for the nerve to heal, the wrist can be splinted in a neutral position with a device that leaves the fingers free to move. The fingers are more functional when the wrist is straight. One can prove this to himself or herself by flexing the wrist and trying to do something useful with the fingers, like write a sentence or pick up a coin. However, use of a splint does not preclude the need for at least daily, passive, range-of-motion exercises.