Rote memorize this info. Then answer the questions at the end. No pain no gain.
Thumb abduction
- Abductor pollicis longus
- Abducts the thumb (i.e., moves the thumb anteriorly / perpendicular to the palm) at the 1st carpometacarpal (CMC) joint; also has extensor function.
- Inserts at the 1st metacarpal.
- Innervated by the posterior interosseous nerve (the continuation of the deep branch of radial nerve).
- Abductor pollicis brevis
- Abducts the thumb at the 1st CMC and metacarpophalangeal (MCP) joints; also has extensor function.
- Inserts at the 1st proximal phalanx.
- Innervated by the recurrent branch of the median nerve.
Pinky-only abduction
- Abductor digiti minimi
- Abducts the pinky at the 5th carpometacarpal joint.
- Enables grasping of large objects while the fingers are outstretched.
- Innervated by the deep branch of ulnar nerve.
2nd-4th-finger abduction
- Dorsal interosseous muscles
- Abduct the ring, middle, and index fingers (i.e., the ring and index movement away from the middle finger + the middle finger movement radially).
- Insert on the proximal phalanges and extensor expansions (specialized connective tissue).
- Innervated by deep branch of ulnar nerve.
- PAD DAB – mnemonic for memorizing actions of dorsal vs palmar interosseous functions – Palmar ADduction, Dorsal ABduction.
- Should be noted that the middle finger has two dorsal interossei attachments and no palmar interossei attachments. Movement of the middle finger medially is referred to as ulnar abduction; movement of the middle finger laterally is referred to as radial abduction.
2nd-5th-finger adduction
- Palmar interosseous muscles
- Adduct the pinky, ring, middle, and index fingers (i.e., the pinky, ring, and index movement toward from the middle finger.
- Insert on the proximal phalanges and extensor expansions (specialized connective tissue).
- Innervated by deep branch of ulnar nerve.
- PAD DAB – mnemonic for memorizing actions of dorsal vs palmar interosseous functions – Palmar ADduction, Dorsal ABduction.
- Note that the pinky is adducted by the palmar interossei, but it is not abducted by the dorsal interossei; the abductor digiti minimi abducts the pinky.
- Wartenberg sign → ulnar nerve palsy resulting in attenuated function of palmar interossei → loss of pinky adduction component → pinky’s normal position is more abducted. There is also attenuated function of the abductor digiti minimi (also ulnar nerve), but the effect of loss of adduction function of palmar interossei is more significant in pinky position. The net result is the extensor digiti minimi remains unopposed, with the abduction positioning favored.
Thumb adduction
- Adductor pollicis
- Adducts the thumb at the 1st CMC joint (i.e., from the abducted position, moves the thumb posteriorly back toward the palm).
- Inserts on 1st proximal phalanx.
- Innervated by the deep branch of ulnar nerve.
- Froment sign = inability to pinch paper between thumb and index finger without bending of the thumb → indicates ulnar nerve palsy affecting adductor pollicis. Patient utilizes flexor pollicis longus.
Opposition and apposition
- Opponens pollicis
- Approximates the tip of the thumb to the tip of the pinky (opposition).
- Approximates the tip of the thumb to the tips of the 2nd-4th fingers (apposition).
- Opposition and apposition are technically a type of thumb flexion.
- Inserts on 1st metacarpal.
- Innervated by the recurrent branch of the median nerve (ulnar nerve in 20% of population).
- Opponens digiti minimi
- Approximates the tip of the pinky to the tip of the thumb.
- This is technically a flexion and lateral rotation combination
- Inserts on 5th metacarpal.
- Innervated by deep branch of ulnar nerve.
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