Question

Froment's sign is positive in cases of weakness of?

• A. Thumb adduction
• B. Thumb abduction
• C. Thumb flexion
• D. Thumb extension

Hint:

It signals ulnar nerve palsy, paralysing the adductor pollicis so the thumb flexes to grip.

Answer 1

The Correct Option is A

Step 1: Froment's sign tests the integrity of the adductor pollicis, a muscle supplied by the ulnar nerve. It therefore detects ulnar nerve palsy through weakness of thumb adduction.

Step 2: The patient is asked to hold a book or sheet of paper between the thumb and the side of the index finger. Normally the adductor pollicis and first dorsal interosseous grip firmly with the thumb kept extended.

Step 3: If the ulnar nerve is injured, the adductor pollicis is paralysed, so the patient compensates by using the flexor pollicis longus (median nerve). This flexes the thumb at the interphalangeal joint to pinch the object.

Step 4: The visible flexion of the terminal thumb joint when trying to hold the object, made more obvious when the examiner pulls it away, is a positive Froment's sign, also called the book test. The defect is weakness of thumb adduction.