Dr. Ebraheim’s educational animated video describes the Froment's Sign Ulnar Nerve Injury.
The Froment’s sign occurs due to weakness of the adductor pollicis muscle in ulnar nerve palsy. The adductor pollicis muscle has two heads. The transverse head originates from the anterior body of the third metacarpal. The oblique head originates from the base of the second and third metacarpals, as well as the trapezoid and capitate bones. The two heads of the adductor pollicis muscle then insert into the base of the proximal phalanx of the thumb and the ulnar sesamoid bone. The muscle is innervated by the deep branch of the ulnar nerve. The adductor pollicis muscle function is to adduct the thumb. It is important in pinch strength. When the ulnar nerve is injured, the adductor pollicis function is lost and thumb adduction will not occur. The Froment’s Sign is used to test the function of the adductor pollicis muscle. When pinching a piece of paper between the thumb and index finger against resistance, the thumb IP joint will flex if the adductor pollicis muscle is weak. The flexion of the thumb occurs by the flexor pollicis longus which is innervated by the median nerve. The flexor pollicis longus, which is innervated by the median nerve, substitutes the function of the adductor pollicis, which is innervated by the ulnar nerve.

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Background music provided as a free download from YouTube Audio Library.
Song Title: Every Step