Median nerve compression at the wrist.

Median nerve decompression at the wrist is one of the most common operative procedures performed by hand surgeons, yet studies report surgical failure rates of 7% to 20%. Symptoms must be coordinated with diagnostic studies. Initial paresthesias should be documented with delayed sensory conduction time. Threshold tests of sensibility, such as the Semmes-Weinstein monofilaments, are more consistent and reliable tests of decreased sensibility than innervation density tests, such as the Weber two-point discrimination test. Thenar atrophy should be documented with electromyographic studies. The median nerve should be evaluated from the fingertips to the cervical spine. Basic laboratory studies should test for collagen disease, thyroid or renal disorders, and diabetes mellitus. Appropriate roentgenograms must be obtained. Patients with normal laboratory and diagnostic studies should be offered nonoperative treatment. Factors that are important in predicting the patient's response to nonoperative treatment include: age over 50 years, constant paresthesias, intermittent paresthesias of more than 10 months duration, stenosing flexor tenosynovitis, and a wrist flexion test (Phalen) that is positive in less than 30 seconds. Fewer than 10% of patients with three or more of these factors present have been cured by nonoperative management. Surgical decompression of the carpal tunnel is done with tourniquet control and optical magnification. A longitudinal "zig-zag" incision is preferred that extends along the thenar crease, then proceeds ulnarly to reach the distal palmar crease at a point in line with the long axis of the ring finger, and then proceeds radially to the tendon of the palmaris longus. After release of the transverse carpal ligament, the motor branch should be explored and decompressed.(ABSTRACT TRUNCATED AT 250 WORDS)