Everybody knows that smacking your funny bone isn’t all that funny, but did you know that the prickling feeling you feel from smacking it isn’t from your bones at all? Instead, the decidedly unpleasant sensation comes from the ulnar nerve, a set of sensitive fibres that runs along your arm and passes behind your elbow joint.

It isn’t actually clear how the funny bone got its name. Some say that it’s a play on words since the upper arm bone, the one between your elbow and shoulder, is called the humerus. Others instead argue that the name is derived from the funny, tingly feeling you get when you strike it the wrong way. We might not know exactly why it’s called the funny bone, but we do know why it hurts so much to hit it.

The ulnar nerve begins in the spine and branches out through the shoulder and down the arm, ending ultimately in the little finger and the adjacent ring finger. As the bundle of neurons travels down your arm, layers of bone and muscle offer protection as it sends and receives signals to and from the muscles of the forearm and the hand.

The problem is that as the ulnar nerve passes the elbow it travels behind a knob of the humerus called the medial epicondyle and through a small, 4mm-long channel called the cubital tunnel, right next to the olecranon, the bony hook where the radius and ulna meet the humerus. And in that spot, the nerve is sandwiched between the bone and the skin, without much in the way of padding or protection.

Cubital tunnel syndrome can actually involve a great deal of pain and discomfort

So when you hit your arm at just the right angle, what you’re doing is squashing the nerve against the medial epicondyle. And when that happens, you get that familiar sensation of hitting your funny bone; that odd mix of numbness and tingling. And because it’s the ulnar nerve responsible for the pain, not the humerus bone itself, that feeling shoots down the rest of your arm and ends in the little and ring fingers.

But as bad as that sounds, for most people the funny feeling they get from striking the ulnar nerve is but a fleeting sensation. After you rub your elbow for a few minutes, the feeling usually passes.

Imagine that as you went about your day you were followed around by someone constantly striking a small mallet into your elbow, hitting your funny bone over and over and over again, and that is what it feels like to have cubital tunnel syndrome. It may not be as common as the similar carpal tunnel syndrome in the hands, but cubital tunnel syndrome can actually involve a great deal of pain and discomfort, and in its most extreme cases can even impair a patient’s use of their hand. It’s the second most common affliction of its type, after carpal tunnel syndrome.

Splints and pillows

Whether the ulnar nerve gets pinched for a long period of time or repeatedly rather than with a quick strike is the basic difference between hitting your funny bone and a diagnosis of cubital tunnel syndrome. The syndrome can develop, for example, if the ulnar nerve snaps back and forth across the medial epicondyle (a raised area of the humerus) as your elbow is bent and straightened over and over again, or it can happen if you hold your elbow in a bent position for too long, such as when you sleep or hold a phone to your face for a long period of time.

Most doctors would first opt for a non-surgical attempt to alleviate the problem before trying surgery. The most obvious prescription is to avoid actions that cause the symptoms of cubital tunnel syndrome. If someone has a habit of keeping their arms bent while they sleep, they can put on a splint before bed, or wrap a pillow or towel around their elbow to keep their arm more relaxed. Those who feel discomfort from holding their phone up can opt for a hands-free alternative. These are small, easy tweaks to basic everyday activities that, for sufferers of more mild forms of cubital tunnel syndrome, can still bring incredible relief.

But as the American Society for Surgery of the Hand explains, sometimes surgery has to be considered. This can involve relocating the nerve to the front of the elbow, or shaving or removing part of a bone to ease pressure on the nerve. The problem is, there’s little consensus as to which form is the best method.

A 1989 study reviewed a century’s worth of published case reports and studies, a dataset representing more than 2000 patients whose suffering from cubital tunnel syndrome required surgery. In it, Baltimore physician A Lee Dellon lamented that “the philosophy of treatment has vacillated from the time when surgeons believed that virtually every case of ulnar nerve compression at the elbow should be operated on because there appeared to be no instances of spontaneous recovery, to the recent realisation that nonoperative management can result in recovery in selected patients.”

More than 25 years later, little has changed. Even in 2014, researchers were still conducting studies comparing surgical alternatives, and earlier this year surgeons Prasad Sawardeker, Katie E Kindt, and Mark E Baratz of Pittsburgh’s Allegheny General Hospital wrote, “no standard exists for the surgical treatment of cubital tunnel… the available evidence at this point is insufficient to identify the best treatment technique”.

So next time you accidentally whack your elbow on the arm of your chair, a car door, or anything else, take heart: it could be much, much worse.

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