What nerve is suspected to be affected if a patient displays a positive Froment's Sign?

A positive Froment's Sign indicates a specific loss of function related to the ulnar nerve. This neurological examination tests the function of the adductor pollicis muscle, which is primarily innervated by the ulnar nerve. When a patient is asked to hold a piece of paper between their thumb and index finger, a positive sign occurs if they flex the thumb at the interphalangeal joint due to weakness in adduction caused by ulnar nerve dysfunction.

In this scenario, the ulnar nerve's impairment leads to reliance on the flexor pollicis longus muscle, which is innervated by the median nerve, resulting in thumb flexion. This indicates that the ulnar nerve, which should be responsible for adducting the thumb, is not functioning properly. Therefore, the manifestation of a positive Froment's Sign directly correlates with an issue involving the ulnar nerve.