ulnar nerve entrapment syndrome / ulnar neuritis neuropathy / claw hand
The symptoms of ulnar nerve entrapment depend on where the nerve is being compressed.
Compression at the elbow, known as cubital tunnel syndrome, causes numbness in the small finger (also known as the "pinkie"), along the half (lengthwise) of the ring finger closest to the small finger, and the back half of the hand over the small finger. Initially, the numbness is transient and usually occurs in the middle of the night or in the morning. The sensation is similar to hitting one's "funny bone," but lasts a bit longer. Over time, the numbness is there all of the time, and weakness of the hand sets in. The "ulnar claw," or a position where the small and ring fingers curl up, occurs late in the disease and is a sign the nerve is severely affected.
The claw hand is worse for Guyon canal stenosis, or nerve compression at the wrist. This is an example of the ulnar paradox. Also, if the nerve is compressed at the wrist, the back of the hand will have normal sensation.
The ulnar nerve passes through many tunnels and outlets which could cause the nerve to be pinched. Some causes or origins noted could be:
Brachial plexus abnormalities
Wrist abnormalities (fractures, Guyon canal problems)
Guyon's Canal Syndrome
Guyon's canal syndrome, sometimes called Guyon's tunnel syndrome, is a common nerve compression affecting the ulnar nerve as it passes through a tunnel in the wrist called Guyon's canal. This problem is similar to carpal tunnel syndrome but involves a completely different nerve. Symptoms include a feeling of pins and needles in the ring and little fingers, and may progress to a burning pain in the wrist and hand followed by decreased sensation in the ring and little fingers. One common cause of this syndrome is from pressure of bicycle handlebars seen with avid cyclists. Another is from hard, repetitive compression against a desk surface while using a computer mouse.
Cubital Tunnel Syndrome
Cubital tunnel syndrome occurs when the ulnar nerve is obstructed during its path along the cubital tunnel; the outer edge of the elbow. This compression of the nerve often leads to a tingling or 'pins and needles' sensation in the little and ring fingers. Most cases will be minor and tend to come and go with time. Common causes are sleeping with the arm folded up, so the hand is at the person's neck and the elbow is sharply bent. These people frequently wake up with tingling in the fingers, because the nerve has been pinched or squeezed while asleep. Treatment of these types of causes are easy to remedy and can involve simply altering sleeping positions to avoid aggravating the elbow area. In more extreme cases however where tingling is persistent, surgery is an option to move the nerve away from the area.
Entrapment of the Ulnar nerve is most likely caused by extended pressure of the elbow on a hard surface repeatedly over a period of time. For example, the resting of the elbows on the arms of a chair while typing at a work station. This condition is also known as drivers elbow, often time caused by resting or bracing the elbow on the arm rest of vehicles over extended periods of time.
Identifying which of the three hand nerves is impinged is usually quite simple. The ulnar nerve innervates the fourth and fifth fingers, and symptoms such as numbness, weakness, and tingling appear there. The ulnar nerve also innervates the intrinsic muscles of the hand, which on paralysis lead to a characteristic clumsiness in ulnar nerve palsy. Clinical tests, like card test, Froment sign, can be easily performed for assessment of ulnar nerve. However, a complete diagnosis should identify the source of the impingement, and further testing may be necessary to determine which of many possible underlying causes is relevant.
Entrapment of the median nerve causes carpal tunnel syndrome, which is characterized by numbness in the thumb, index, middle, and half of the ring finger. Compression of the radial nerve causes numbness of the back of the hand and thumb, and is much more rare.
Carpal tunnel syndrome is largely genetic and the same is probably true of cubital tunnel syndrome although it has not been studied.
The idea that cubital tunnel syndrome can be prevented by good posture and proper use of the elbow and arms, such as sleeping with the arm straight at the elbow instead of keeping it tightly bent, or keeping the head properly centered over the cervical spine instead of slouching is probably wishful thinking, and may unfairly stigmatize hand use. A recent example of this is popularization of the concept of cell phone elbow,
Effective treatment generally requires resolving the underlying cause.
Surgery to release the nerve trapped or decompress.
Surgery may be required for some causes, such as thoracic outlet syndrome.
Most patients diagnosed with cubital tunnel syndrome have advanced disease (atrophy, static numbness, weakness) that reflect permanent nerve damage that will not recover after surgery.  When diagnosed prior to atrophy, weakness or static numbness, the disease can be arrested with operative treatment and intermittent symptoms usually resolve.
^ Lozano-Calderón S, Anthony S, Ring D. The quality and strength of evidence for etiology: example of carpal tunnel syndrome. J Hand Surg Am. 2008 Apr;33(4):525-38. http://www.ncbi.nlm.nih.gov/pubmed/18406957
^ Thomas, Jennifer (02 June 2009). "'Cell Phone Elbow' -- A New Ill for the Wired Age". HealthDay News. Retrieved 02 June 2009.