Ulnar neuropathy is a disorder involving the ulnar nerve. Ulnar neuropathy may be caused by entrapment of the ulnar nerve at the elbow or wrist with resultant numbness and tingling into the fourth and fifth fingers.
Motor function can be assessed by testing for a positive Froment's sign, or making an OK sign (which the patient will be unable to do). Little finger abduction can be tested as well.
Both the onset and progress of the symptoms can be variable. Although the answer is frequently negative, one should ask specifically about trauma and pressure to the arm and wrist, especially the elbow, the medial side of the wrist, and other sites close to the course of the ulnar nerve.
Many patients complain of sensory changes in the fourth and fifth digits. Rarely, a patient actually notices that the unusual sensations are mainly in the medial side of the ring finger (fourth digit) rather than the lateral side, corresponding to the textbook sensory distribution. Sometimes the third digit is also involved, especially on the ulnar (i.e., medial) side. The sensory changes can be a feeling of numbness or a tingling or burning. Pain rarely occurs in the hand. Complaints of pain tend to be more common in the arm, up to and including the elbow area. Indeed, the elbow is probably the most common site of pain in an ulnar neuropathy. Occasionally, patients specifically say “I have pain in my elbow,” “I have pain in my funny bone,” or even “I have pain in this little groove in my elbow,” but usually they are not quite so explicit unless prompted. Patients rarely notice specific muscle atrophy.
Weakness may also be a presenting complaint, but the complaint may be expressed in subtle ways. One traditional sign of ulnar neuropathy is a complaint of weakness. The patient complains that the little finger gets caught on the edge of the pants pocket when he or she puts the hands into the pocket. Because of the ulnar dysfunction the patient cannot adduct the fifth digit tightly against the fourth because of weakness of the interosseous muscles. The muscle that extends the fifth digit at the metacarpal phalangeal joint (extensor digiti quinti) is radially innervated and it inserts on the ulnar side of the joint. Normally this muscle is opposed by ulnar innervated muscles that flex the joints, but with an ulnar neuropathy the muscle is relatively unopposed so it pulls the finger up and to the ulnar side. This is why the finger tends to stick out and get caught on objects.
The patient may also express the complaint of weakness by saying “my grip is weak.” Many of the grip muscles are ulnar. Also, when someone tries to grip powerfully, the hand usually deviates in the ulnar direction under the influence of the flexor carpi ulnaris. If this ulnar deviation is impaired, the grip mechanism does not work optimally even for the muscles that are unimpaired.
Sometimes a patient notices that his pincer grip (pinching with the thumb and index finger) is weak. Two of the key muscles involved in this movement are the adductor pollicis (which adducts the thumb) and first dorsal interosseous, which adducts the index finger. Not only may the pincer grip be weak in an ulnar neuropathy, the median innervated flexor pollicis longus partially compensates for the weakened adductor pollicis and the thumb flexes at the distal joint. Usually a patient does not notice the thumb flexion, but when demonstrated by the examiner, this flexion is considered to be Froment sign.
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