Muscles of Finger Abduction and Thumb Flexion

Fingers, Joints Abduction, and Thumb Flexion

• Objective: Students will be able to identify the muscles involved in finger abduction and thumb flexion, the range of motion, and the effects of weakness of thumb flexors.

• Content:

  • The anatomy of the primary muscles involved in finger abduction and thumb flexion.
  • Range of motion for finger abduction and thumb flexion (0° to 20°-25° for fingers, and ranges for thumb).
  • Effects of weakness in thumb flexor muscles.

Finger Abduction Motion

• Primary Muscles:

  • Interossei dorsales
  • Abductor digiti quinti

• Range of Motion: 0° to 20°-25° (finger abduction)

• Anatomy of Interossei Dorsales:

  • Origin: Inner aspects of metacarpal shafts.
  • Insertion: Proximal phalanges, dorsal extensor expansion on radial side of index and middle fingers, ulnar side of middle and ring fingers.
  • Nerve Supply: Ulnar nerve.
  • Action: Abduct fingers away from axis of middle finger. Flex the metacarpophalangeal joint while extending the interphalangeal joint.

Anatomy of Abductor Digiti Quinti

• Origin: Pisiform bone, pisohamate ligament, flexor retinaculum
• Insertion: Ulnar side of proximal phalanx of little finger, extensor expansion
• Nerve Supply: Ulnar nerve
• Action: Abducts little finger at the metacarpophalangeal joint

Flexion of Metacarpophalangeal and Interphalangeal Joints of Thumb

• Primary Muscles:

  • Flexor pollicis longus
  • Flexor pollicis brevis

• Range of Motion:

  • Thumb-metacarpophalangeal joint flexion: 0° to 60°-70°
  • Thumb interphalangeal joint flexion: 0° to 90°

• Anatomy of Flexor Pollicis Longus:

  • Origin: Anterior surface of radius below the anterior oblique line and adjacent interosseous membrane.
  • Insertion: Base of distal phalanx of thumb
  • Nerve Supply: Median nerve
  • Action: Flexes distal phalanx of thumb

• Anatomy of Flexor Pollicis Brevis:

  • Origin: Flexor retinaculum and tubercle of trapezium
  • Insertion: Base of proximal phalanx of thumb
  • Nerve Supply: Median nerve
  • Action: Flexes metacarpophalangeal joint of thumb

Effects of Weakness

• Flexor pollicis longus:

  • Weakness reduces distal phalanx flexion, making it difficult to hold objects and pick things up.

• Flexor pollicis brevis:

  • Weakness reduces proximal phalanx flexion, making it difficult to grip objects.

This quiz focuses on the muscles involved in finger abduction and thumb flexion, exploring their anatomy, range of motion, and the impact of muscle weakness. Students will identify key muscles like the interossei dorsales and learn about their function and nerve supply.