The Hand

Abductor Pollicis Brevis

Patient Position:

Forearm supinated with the palm up.

Needle Insertion:

Insert the needle obliquely from the radial side of the thenar eminence at about the proximal half of the first metacarpal bone.

Activation:

Abduct the thumb with some medial rotation.

Clinical Notes:

If inserted too medially in the thenar eminence, the needle will penetrate the flexor pollicis brevis (superficial or deep head); if too deep, opponence pollicis will be penetrated. It is thin and is the most superficial muscle of the thenar muscles. In severe median neuropathy, a needle recording from this muscle may not eliminate the volume-conducted response from adjacent ulnar nerve innervated muscles. This muscle is very painful to needle!

Innervation:

C8, T1-lower trunk-medial cord-median nerve (recurrent branch).

Origin:

Flexor retinaculum, scaphoid, trapezium.

Insertion:

Radial side of the base of the proximal phalanx of thumb, and lateral sesamoid bone of the thumb.

Figure 11-1. Abductor pollicis brevis.

Opponens Pollicis

Patient Position:

Palm up (supination of hand).

Needle Insertion:

This muscle is deep to the abductor pollicis brevis in the thenar eminence. Insert the needle close to the anterior surface of the first metacarpal bone.

Activation:

Opposition of the thumb or flexion of the metacarpal bone of the thumb.

Clinical Notes:

It is found deep to the abductor pollicis brevis. It occasionally may be innervated by the deep branch of the ulnar nerve.

Innervation:

C8, T1-lower trunk-medial cord-median nerve (recurrent branch).

Origin:

Flexor retinaculum and trapezium.

Insertion:

Lateral border of the metacarpal bone.

Figure 11-2. Opponens pollicis.

Flexor Pollicis Brevis—Superficial and Deep Head

Patient Position:

Supine with the forearm supinated and palm up.

Needle Insertion:

The thenar eminence can be divided into a lateral half and a medial half by a longitudinal section. Insert the needle into the medial-half area of the thenar eminence.

Activation:

Flex the thumb (proximal phalanx); it also aids opposition and adduction.

Clinical Notes:

This muscle is found medial to the abductor pollicis brevis and is somewhat overlapped by it. It is particularly active in a firm grip between the thumb, index, and middle fingers.

Innervation:

C8, T1-superficial head, median nerve (recurrent branch); deep head, ulnar nerve.