Hitting Your Funny Bone Isn't Funny

Hitting Your Funny Bone Isn't Funny
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When you hit your funny bone, you can feel an electric shock (tingling/numbness) in the hand and forearm. You're really not hitting the funny bone alone, but you are hitting the funny bone and the ulnar nerve. That is why it feels funny when you hit the bone. If the trauma is severe, you may damage the nerve; the ulnar nerve is known to be sensitive. When you hit this nerve, you may hurt its feelings.

The medial epicondyle (Figure 1) is a bony prominence around the elbow towards the inside. The ulnar nerve runs behind the medial epicondyle. The course of the ulnar nerve is as follows. The ulnar nerve originates from the medial cord of the brachial plexus. The nerve runs down the arm where it passes behind the medial epicondyle of the humerus and travels into the forearm and hand. The ulnar nerve can become pinched in different locations including the thoracic outlet region, around the elbow or at the wrist (Figure 2).



When the ulnar nerve is entrapped around the elbow, it is called cubital tunnel syndrome. As the ulnar nerve passes behind the elbow, it may become compressed or irritated. The ulnar nerve travels through a tunnel of tissue (cubital tunnel) that runs behind the medial epicondyle. Pressure on the nerve at the elbow can cause numbness or pain in the elbow, hand, wrist or fingers (Figure 3).


The patient will describe symptoms of pain and numbness in the elbow as well as tingling in the ring and little fingers. More severe symptoms of cubital tunnel syndrome include weak or clumsy hand, weakness affecting the ring and little fingers and muscle wasting. Claw hand deformity will be present if the compression is below the elbow. Claw hand is flexion of the fingers by a functional profundus muscle for the 4th and 5th fingers (Figure 4).


The symptoms of cubital tunnel syndrome are worsened by performing activities that require bending of the elbow. Keeping the elbow extended, especially during the night will often relieve the pressure being placed on the ulnar nerve at the elbow.

Differential Diagnosis:
Pain could be due to injury of the cervical spine C8 nerve root. Another differential diagnosis may be thoracic outlet syndrome. Thoracic outlet syndrome is the entrapment at the area between the rib cage and the collar bone. A pancoast tumor (apical lung tumor) may also be a differential diagnosis.

Clinical Examination:
A tapping technique is performed to test for symptoms of ulnar nerve entrapment at the cubital tunnel. This test is called the Tinel's sign at the elbow. The elbow flexion test can also be used to help test for symptoms. During testing using the Froment's sign, the thumb compensates to resist the pull on the paper by flexing the IP joint (Figure 5).


Treatment for cubital tunnel syndrome can be conservative including NSAIDs, night splint, elbow pads, therapy or injections. Surgery may also be utilized to release the nerve with or without transposition, the type of transposition is controversial.

There is a bad prognosis if there is intrinsic muscle atrophy. A complication of surgery is injury to the medial antebrachial cutaneous nerve. Neurolysis is not helpful.

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