Thumb Muscle Anatomy Lecture

Introduction

• Focus: Drawing the muscles of the thumb
• Goal: Clarify the anatomy and how muscles surround the thumb

Extrinsic Muscles (Dorsal Aspect)

Extensor Pollicis Longus (EPL)

• Origin: Posterior surface of the ulna (middle third)
• Pathway: Through third dorsal compartment of the dorsal retinaculum at the wrist
• Insertion: Distal to the interphalangeal joint
• Notes: Becomes part of the dorsal apparatus (triangular group of fibers starting at metacarpal phalangeal joint)

Extensor Pollicis Brevis (EPB)

• Origin: Posterior surface of the radius
• Pathway: Through first dorsal compartment
• Insertion: Distal to the metacarpal phalangeal joint (variable)

Abductor Pollicis Longus (APL)

• Origin: Posterior surface of the ulna, interosseous membrane, and radius
• Pathway: Through the first dorsal compartment with EPB
• Insertion: Just distal to the CMC joint (variable and may extend more distally)

Extrinsic Muscles (Palmar Aspect)

Flexor Pollicis Longus (FPL)

• Origin: Anterior surface of the interosseous membrane, medial border of the ulna, medial epicondyle
• Pathway: Through the carpal tunnel along with finger flexors
• Insertion: Just distal to the interphalangeal joint

Intrinsic Muscles

Opponens Pollicis

• Origin: Flexor retinaculum, tubercle of the trapezium
• Insertion: Along the entire surface of the first metacarpal
• Function: Pulls first metacarpal into rotation, does not go distal to the MP joint

Adductor Pollicis

• Heads:
  • Oblique Head: From capitate, base of second and third metacarpals
  • Transverse Head: From third metacarpal across to the dorsal apparatus
• Insertion: Through the web space, into the dorsal apparatus, and base of the proximal phalanx
• Function: Flex MP joint, extend IP joint, adduct

Flexor Pollicis Brevis (FPB)

• Heads:
  • Deep Head: Arises from trapezoid and capitate
  • Superficial Head: Arises from flexor retinaculum and tubercle of the trapezium
• Insertion: Into the dorsal apparatus, similar to the adductor
• Function: Flex MP joint, extend IP joint

Abductor Pollicis Brevis (APB)

• Origin: Flexor retinaculum, trapezium, scaphoid
• Insertion: Into the dorsal apparatus, proximal phalanx
• Function: Lies on radial aspect of first metacarpal

Additional Muscle Influencing the Thumb

First Dorsal Interosseous

• Bellies:
  • Ulnar Belly: Arises from the first metacarpal, inserts into the dorsal apparatus
  • Radial Belly: Arises from first metacarpal, inserts into the tubercle and possibly the dorsal apparatus
• Function: Influences thumb CMC joint stability

Conclusion

• Summarized the origin, insertion, and function of the 8 thumb muscles
• Included influence of the first dorsal interosseous on thumb motion