Describe Phalen's sign.

Phalen's sign is a clinical test used to assess for carpal tunnel syndrome, which is characterized by compression of the median nerve as it travels through the wrist. The correct description involves the patient holding their wrists in full flexion—typically by pressing the backs of the hands together for an extended period, usually for about a minute. This position increases pressure on the median nerve, and if the patient experiences tingling or numbness in the thumb, index, middle finger, and part of the ring finger, it is considered a positive Phalen's sign.

This symptom occurs because the flexed position exacerbates the existing compression on the median nerve, thus eliciting the characteristic pain or paresthesia associated with carpal tunnel syndrome. The other choices describe different clinical signs or conditions, such as the ulnar nerve distribution symptoms or general weakness, but they do not accurately reflect the specific mechanics and implications of Phalen's sign as it pertains to the median nerve's response to wrist flexion.