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144 Chapter 4 Hand and Wrist

Figurę 4-68. Assessing thumb palmar adduction strength.

an action powered primarily by the adductor pollicis. To perform Froments test, the patient is asked to make tight fists with both hands and to place the hands against cach other. The extended thumbs are then used to pinch an index card against the radial side of the index fingers. The patient is instructed to pinch the card as tightly as possi-ble and to attempt to prevent the examiner from with-drawing the card (Fig. 4-69A). The patient should normally be able to resist withdrawal of the card while maintaining the interphalangeal joints of the thumbs in extension. If the adductor pollicis of one hand is weak, the patient usually attempts to substitute for the lost strength by firing the flexor pollicis longus. This action causes the interphalangeal joint of the thumb to visibly flex, an action known as Fromenfs sign (Fig. 4-69D). Froments sign usually signifies an isolated ulnar nerve palsy, as the adductor pollicis is innervated by the ulnar nervc, while the flexor pollicis longus is innervated by the median nerve.

True opposition of the thumb requires proper function of both the abductor pollicis brevis and the opponens pollicis muscles. The abductors of the thumb participate in this complex motion by bringing the thumb away from the palm, but it is the opponens pollicis that rotates it so that it faces the other fingers. Bccause opposition is usually tested by bringing the tips of the thumb and the little finger together, the opponens digiti tninimi also participates in this action. It is the opponens pollicis, however, that is of primary func-tional significance and interest. To test the strength of opposition, the examiner asks the patient to touch the tips of the thumb and the little finger together. Because the thumb flexors and adductors can bring the tip of the

Figurę 4-69. Froments test. A, Normal. B, Abnormal.