1e - Muscles of the Posterior Forearm and Intrinsic Hand Muscles

Question 1

Extensor carpi radialis longus - Origin, Insertion, Action and Innervation

Answer 1

Origin: Lateral supracondylar ridge of humerus.
Insertion: Base of second metacarpal.
Primary action: Extends hand (with Extensor Carpi Ulnaris) and abducts hand
Innervation: Radial

Question 2

Extensor carpi radialis brevis - Origin, Insertion, Action and Innervation

Answer 2

Origin: Lateral epicondyle of humerus.
Insertion: Base of third metacarpal.
Primary action: Extends and abducts hand
Innervation: Deep branch of Radial

Question 3

Extensor digitorum - Origin, Insertion, Action and Innervation

Answer 3

Origin: Lateral epicondyle of humerus.
Insertion: By four tendons into extensor expansions and distal phalanges of fingers II-V
Primary action: Primer mover of finger extension.
Other actions: Extends hand and abduct (flare) fingers.
Innervation: Posterior interosseous (deep branch of radial)

Question 4

Extensor carpi ulnaris - Origin, Insertion, Action and Innervation

Answer 4

Origin: Lateral epicondyle of humerus and posterior border of ulna.
Insertion: Base of fifth metacarpal.
Primary action: Extends hand (with Extensor Carpi Radialis) and adducts hand (with Flexor Carpi Ulnaris).
Innervation: Posterior interosseous (deep branch of radial)

Question 5

Supinator - Origin, Insertion, Action and Innervation

Answer 5

Origin: Lateral epicondyle of humerus, radial collateral and annular ligaments,supinator fossa and crest of ulna.
Insertion: Lateral, posterior, and anterior of proximal 1/3 of radius.
Primary action: Assist biceps to supinate forearm.
Innervation: Deep branch of radial

Question 6

Abductor pollicis longus - Origin, Insertion, Action and Innervation

Answer 6

Origin: Posterior surface of radius, ulna, and interosseous membrane.
Insertion: Base of first metacarpal and trapezium.
Primary action: Abducts and extends thumb.
Innervation: Posterior interosseous (deep branch of radial)

Question 7

Extensor pollicis longus - Origin, Insertion, Action and Innervation

Answer 7

Origin: Posterior surface of middle 1/3 of ulna and interosseous membrane.
Insertion: Distal thumb phalanx.
Primary action: Extends thumb at carpometacarpal and interphalangeal joints.
Innervation: Posterior interosseous (deep branch of radial)

Question 8

Extensor pollicis brevis - Origin, Insertion, Action and Innervation

Answer 8

Origin: Posterior surface of radius and interosseous membrane.
Insertion: Base of proximal phalanx of thumb.
Primary action: Extends thumb at carpometacarpal joint.
Innervation: Posterior interosseous (deep branch of radial)

Question 9

Extensor indicis - Origin, Insertion, Action and Innervation

Answer 9

Origin: Posterior surface of distal ulna and interosseous membrane.
Insertion: Extensor expansion of index finger. Joins tendon of extensor digitorum.
Primary action: Extends index finger.
Other action: Hand extension.
Innervation: Posterior interosseous (deep branch of radial)

Question 10

Abductor pollicis brevis - Origin, Insertion, Action and Innervation

Answer 10

Origin: Flexor retinaculum and nearby carpals.
Insertion: Lateral base of thumb’s proximal phalanx.
Primary action: Abducts thumb at carpometacarpal joint.
Innervation: Recurrent branch of medial

Question 11

Flexor pollicis brevis - Origin, Insertion, Action and Innervation

Answer 11

Origin: Flexor retinaculum and nearby metacarpals.
Insertion: Lateral base of thumb’s proximal phalanx.
Primary action: Flexes thumb at carpometacarpal joint.
Innervation: Recurrent branch of medial

Question 12

Opponens pollicis - Origin, Insertion, Action, and Innervation

Answer 12

Origin: Flexor retinaculum and trapezium.
Insertion: Whole anterior side of metacarpal I.
Primary action: Opposition (moves thumb to touch tip of little finger).
Innervation: Recurrent branch of medial

Question 13

Adductor pollicis - Origin, Insertion, Action and Innervation

Answer 13

Origin: Capitate bone and bases of metacarpals II-IV; front of metacarpal III.
Insertion: Medial side of base of thumb’s proximal phalanx.
Primary action: Adducts and helps to oppose the thumb.
Innervation: Deep branch of ulnar

Question 14

Abductor digiti minimi - Origin, Insertion, Action and Innervation

Answer 14

Origin: Pisiform bone.
Insertion: Medial side of proximal phalanx of little finger.
Primary action: Abducts little finger at metacarpophalangeal joint.
Innervation: Deep branch of ulnar

Question 15

Flexor digiti minimi brevis - Origin, Insertion, Action and Innervation

Answer 15

Origin: Flexor retinaculum and hamate bone.
Insertion: Medial side of proximal phalanx of little finger.
Action: Flexes little finger at metacarpophalangeal joint.
Innervation: Deep branch of ulnar

Question 16

Opponens digiti minimi - Origin, Insertion, Action and Innervation

Answer 16

Origin: Flexor retinaculum and hamate bone.
Insertion: Most of length of medial side of metacarpal V.
Primary action: Helps in opposition. Brings metacarpal V toward thumb to cup the hand.
Innervation: Deep branch of ulnar

Question 17

Lumbricals - Origin, Insertion, Action and Innervation

Answer 17

Origin: Lateral side of each tendon of Flexor Digitorum Profundus in palm.
Insertion: Lateral edge of extensor expansion on first phalanx of fingers II-V.
Primary action: Flex fingers at metacarpophalangel joints but maintain extension of fingers at interphalangeal joints.
Innervation: Median [lateral 2] and Ulnar [medial 2]

Question 18

Palmar interossei - Origin, Insertion, Action and Innervation

Answer 18

Origin: Sides of each metacarpal that faces the mid axis of the hand (metacarpal III), but absent from metacarpal III.
Insertion: Extensor expansion on first phalanx on each finger (except finger III) on side facing midaxis of hand.
Primary action: Adducts fingers.
Other action(s): Acts with lumbricals to extend fingers at interphalangeal joints and flex them at metacarpophalangeal joints.
Innervation: Ulnar

Question 19

Dorsal interossei - Origin, Insertion, Action and Innervation

Answer 19

Origin: Sides of metacarpals (minus medial side of V and lateral of I).
Insertion: Extensor expansion over first phalanx of fingers II-IV on side opposide of midaxis of hand (finger III), but on both sides of finger III.
Primary action: Abduct fingers.
Other action(s): Extend fingers at interphalangeal joints and flex them at metacarpophalangeal joints.
Innervation: Ulnar

Question 20

What muscle provide excellent tendon grafts and why?

Answer 20

The palmaris longus; has little functionality. Its absence is sometimes undetectable.

Question 21

What are the ‘extensor expansions’?

Answer 21

Aponeuroses of extensor muscles that run into the dorsum of the hand.
Divides into three bands:
1) 2 lateral bands that stretch from proximal phalanx to distal phalanx.
2) Single median band down the middle on the back of the proximal phalanx to the base of the middle phalanx.
3) The retinacular ligament that runs obliquely along middle phalanx connecting fibrous digital sheath (anterior) to extensor expansions (posterior)