The patient is asked to hold a piece of paper between the thumb and index finger (pinch mechanism) against either the pull of the patient’s contralateral hand or the pull of the examiner’s hand.
The muscle for this motion is the adductor pollicis, which is supplied by the ulnar nerve.
Alternatively, test the patient’s ability to grasp a sheet of paper held between the thumb and the anterior aspect of the index metacarpal.
What does a positive Froment sign mean?
Froment sign is Positive if the paper is pulled away by the examiner because of weakness or loss of function in adductor pollicis muscle, where the patient flexes the thumb interphalangeal joint in an attempt to hold on to paper (due to contraction of the flexor pollicis brevis, which is supplied by the median nerve).
There may be additional weakness or paralysis of the interosseous muscles and/or the third and fourth lumbrical muscles resulting in the typical claw hand deformity.
Occasional volar hypesthesia on the ring and little fingers is also a characteristic sign.
There is also a pseudo Froment sign, where the interphalangeal joint of the involved thumb may not have overt flexion but has a distinctly different appearance than the uninvolved side. This finding may especially be noted in patients with ligamentous laxity and hypermobile joints.3
Adductor Pollicis (AP):
The AP arises from two heads:
The transverse head originates from the ventral surface of the shaft of the third metacarpal,
while the oblique head originates from the trapezium, trapezoid, and capitate bones, and the base of the second and third metacarpal bone.
The AP inserts on the ulnar side of the base of the proximal phalanx of the thumb and is innervated by the deep branch of the ulnar nerve.
The AP functions to adduct the thumb and aids in thumb opposition.
Zancolli and Cozzi4 believe that the oblique head of the adductor pollicis has dual ulnar and median innervation in 35% of cases, whereas its transverse head is practically always (96%) innervated by the ulnar nerve.
Clinical Tests for the Musculoskeletal System 3rd Edition.
Dutton’s Orthopaedic Examination, Evaluation, And Intervention 3rd Edition.
Christopher J. Dy and Susan E. Mackinnon: Ulnar neuropathy: evaluation and management. Curr Rev Musculoskelet Med. 2016 Jun; 9(2): 178–184. PMID: 27080868
Zancolli EA, Cozzi EP: Atlas of surgical anatomy of the hand, New York, 1992, Churchill Livingstone.