WHAT IS IT?
Ulnar nerve entrapment occurs when one of the nerves in the arm (the ulnar nerve) becomes compressed and can't 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 (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." Beyond the elbow, the nerve travels under muscles on the inside of the arm, and into the hand on the pinky side of the palm. When the nerve goes into the hand, it travels through another tunnel (Guyon's canal). 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 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.
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 you are driving or talking on the phone. Some people wake up at night because their fingers are numb. You may also have weakness of grip and difficulty with finger coordination (such as typing or playing an instrument). 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 you experience any of the symptoms.
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, or 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.
TREATMENT OPTIONS: NONSURGICAL
- Avoid frequent use of the arm with the elbow bent. If you use a computer frequently, make sure that your chair is not too low. Do not rest the elbow on the armrest.
- Avoid leaning on the elbow or putting pressure on the inside of the arm. For example, do not drive with the arm resting on the open window.
- Keep the elbow straight at night when you are sleeping. This can be done by wrapping a towel around the straight elbow, wearing an elbow pad backwards, or using a special brace.
TREATMENT OPITIONS: SURGICAL
If you are not improving with the strategies listed above, if the nerve is very compressed, or if you have muscle wasting, the doctor may recommend surgery to take pressure off of the nerve. Most often, the surgery is done around the elbow, but it can be done at the wrist if that is the place of the compression. Sometimes, the nerve is compressed in both places, so surgery is done at both the elbow and the wrist.
Surgeons use various ways to relieve compression from the nerve around the elbow. All of the operations involve making an incision around the elbow. In one operation, only the "roof" is taken off of the cubital tunnel. This tends to work best when the nerve compression is mild. More commonly, the nerve is moved from its place behind the elbow to a new place in front of the elbow. This is called an anterior transposition of the ulnar nerve. The nerve can be moved to lie under the skin and fat but on top of the muscle (subcutaneous transposition), within the muscle (intermuscular transposition) or under the muscle (submuscular transposition).