Ulnar nerve entrapment occurs when the ulnar nerve in the arm becomes compressed. When this happens, the nerve does not function normally.

The ulnar nerve is one of the three main nerves in the arm. It travels from under the collarbone and along the inside of the upper arm. It passes through a tunnel of tissue (the cubital tunnel) behind the inside of the elbow. Here you can feel the nerve through the skin. It is commonly called the " funny bone. " (bottom left figure)

Beyond the elbow, the nerve travels under muscles on the inside of the arm and into the hand on the side of the palm with the little finger. As the nerve enters the hand, it travels through another tunnel (Guyon's canal).

The nerve functions to give sensation to the little finger and the half of the ring finger that is near the little finger. It also controls most of the little muscles in the hand that help with fine movements, and some of the bigger muscles in the forearm that help to make a strong grip. (bottom right figure)

The ulnar nerve runs behind the elbow on the inside of the arm. The upper arm bone (humerus) has a groove on the back where the nerve lies. Here the nerve can be felt as the " funny bone. " The ulna is the forearm bone that makes the point of the elbow when it is bent.

The ulnar nerve gives sensation to the little finger and to half of the ring finger on both the palm and back side of the hand.

The most common place where the nerve gets compressed is behind the elbow. Sometimes it gets compressed at the wrist, beneath the collarbone, or as it comes out of the spinal cord in the neck.

The median nerve, which is involved in carpal tunnel syndrome, gives sensation to the thumb, index finger, long finger, and half of the ring finger on the palm side. Tingling in this area is rarely a symptom of ulnar nerve entrapment.

Many people sleep with their arms curled up like this. Sleeping with the elbow bent can aggravate symptoms of ulnar nerve compression and cause you to wake up at night with your fingers asleep.

It is not known exactly what causes compression of the ulnar nerve. Some factors can make it more likely that the nerve will be compressed. These include:

• Prior fractures of the elbow
• Bone spurs
• Swelling of the elbow joint
• Cysts

A direct blow to the inside of the elbow, leaning on the elbow for prolonged periods, or repetitive activity that requires a bent elbow can irritate the nerve if it is already compressed.

If the ulnar nerve is compressed at the wrist, the cause is more likely to be a cyst in Guyon's canal.

Ulnar nerve entrapment can give symptoms of " falling asleep " in the ring finger and little finger, especially when the elbow is bent. There may be an aching pain on the inside of the elbow. In some cases, it may be harder moving the fingers in and out or manipulating objects.

Carpal tunnel syndrome has similar symptoms, but involves a different nerve (the median nerve). Carpal tunnel syndrome typically causes tingling in the thumb, index finger, and long finger.

Numbness and tingling in the ring finger and little finger are common symptoms of ulnar nerve entrapment. Often, these symptoms come and go. They happen more often when the elbow is bent, such as when driving or holding the phone. Some people wake up at night because their fingers are numb.

Weakening of the grip and difficulty with finger coordination (such as typing or playing an instrument) may occur.

If the nerve is very compressed or has been compressed for a long time, muscle wasting in the hand can occur. Once this happens, muscle wasting cannot be reversed. For this reason, it is important to see the doctor as soon as any of the symptoms are noticed.

Always see an orthopaedist if there are having symptoms of ulnar nerve entrapment that interfere with normal activities or last more than a few weeks.

The doctor will examine the arm to determine where the nerve is compressed. If the nerve is irritated, tapping over the nerve at the " funny bone " can cause a shock into the little finger and ring finger, although this can happen when the nerve is normal as well.

The doctor will probably move the shoulder, elbow and wrist to see if any of these cause symptoms. The doctor will test the sensation in the fingers.

Although most causes of compression of the ulnar nerve cannot be seen on an X-ray, the doctor may take an X-ray of the elbow or wrist to look for bone spurs, arthritis, or other places that the bone may be compressing the nerve.

If the doctor thinks that the nerve is compressed at the wrist, a computed tomographic (CT) scan or a magnetic resonance image (MRI) may be recommended to see if a cyst or other structure is the cause of the compression.

The doctor may recommend nerve conduction studies. These are special tests to determine how well the nerve is working and to help localize the area of compression. Nerves work like wires; when the nerve is not working well, it takes too long for the nerve to conduct. During this test, the nerve is stimulated in one place. The amount of time it takes for the response to be conducted to another place is determined. The area where the nerve conduction takes too long is likely to be the place where the nerve is compressed.

Sometimes, a small needle is put into some of the muscles that the ulnar nerve controls. This can determine if there is any evidence of muscle wasting.

Unless there is a lot of muscle wasting, nonsurgical treatment will probably be the initial treatment.