Ulnar nerve entrapment (Cubital Tunnel Syndrome) occurs when the ulnar nerve in the arm becomes compressed or irritated. The ulnar nerve is one of the three main nerves in your arm. It travels from your neck down into your hand, and can be constricted in several places along the way. Depending upon where it occurs, this pressure on the nerve can cause numbness or pain in your elbow, hand, wrist, or fingers.
Sometimes the ulnar nerve gets compressed at the wrist, beneath the collarbone, or as it comes out of the spinal cord in the neck. The most common place where the nerve gets compressed is behind the elbow.
When the nerve compression occurs at the elbow, it is called “cubital tunnel syndrome.”
In many cases of cubital tunnel syndrome, the exact cause is not known. The nerve is especially vulnerable to compression at the elbow because it must travel through a narrow space with very little soft tissue to protect it.
The ulnar nerve runs behind the elbow on the inside of the arm.
Common Causes of Compression
There are several things that can cause pressure on the nerve at the elbow:
- When your bend your elbow, the ulnar nerve stretches around the boney ridge of the medial epicondyle. Because this can irritate the nerve, keeping your elbow bent for long periods or repeatedly bending your elbow can cause painful symptoms.
- For example, many people sleep with their elbows bent. This can aggravate symptoms of ulnar nerve compression and cause you to wake up at night with your fingers asleep.
- In some people, the nerve slides out from behind the medial epicondyle when the elbow is bent. Over time, this sliding back and forth may irritate the nerve.
- Leaning on your elbow for long periods of time can put pressure on the nerve.
- Fluid buildup in the elbow can cause swelling that may compress the nerve.
- A direct blow to the inside of the elbow can cause pain, electric shock sensation, and numbness in the little and ring fingers. This is commonly called “hitting your funny bone.”
- Sleeping with your elbow bent can aggravate symptoms.
Some factors put you more at risk for developing cubital tunnel syndrome. These include:
- Prior fracture or dislocations of the elbow
- Bone spurs/ arthritis of the elbow
- Swelling of the elbow joint
- Cysts near the elbow joint
- Repetitive or prolonged activities that require the elbow to be bent or flexed
Cubital tunnel syndrome can cause an aching pain on the inside of the elbow. Most of the symptoms, however, occur in your hand.
Ulnar nerve entrapment can give symptoms of “falling asleep” in the ring finger and little finger, especially when your elbow is bent. In some cases, it may be harder to move your fingers in and out, or to manipulate objects.
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. These symptoms are usually seen in more severe cases of nerve compression.
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 your doctor if symptoms are severe or if they are less severe but have been present for more than 6 weeks.
Medical History and Physical Examination
After discussing your symptoms and medical history, your doctor will examine your arm and hand to determine which nerve is compressed and where it is compressed.
Some of the physical examination tests your doctor may do include:
- Tap over the nerve at the funny bone. If the nerve is irritated, this can cause a shock into the little finger and ring finger — although this can happen when the nerve is normal as well.
- Check whether the ulnar nerve slides out of normal position when you bend your elbow.
- Move your neck, shoulder, elbow, and wrist to see if different positions cause symptoms.
- Check for feeling and strength in your hand and fingers
- X-rays. These imaging tests provide detailed pictures of dense structures, like bone. Most causes of compression of the ulnar nerve cannot be seen on an x-ray. However, your doctor may take x-rays of your elbow or wrist to look for bone spurs, arthritis, or other places that the bone may be compressing the nerve.
Nerve conduction studies. These tests can determine how well the nerve is working and help identify where it is being compressed.
Nerves are like “electrical cables” that travel through your body carrying messages between your brain and muscles. When a nerve is not working well, it takes too long for it to conduct.
During a nerve conduction test, the nerve is stimulated in one place and the time it takes for there to be a response is measured. Several places along the nerve will be tested and the area where the response takes too long is likely to be the place where the nerve is compressed.
Nerve conduction studies can also determine whether the compression is also causing muscle damage. During the test, small needles are put into some of the muscles that the ulnar nerve controls. Muscle involvement is a sign of more severe nerve compression.