Thumb Anatomy

Description

Insertion of thumb muscles

Left: Overview of the thenar muscles as visible after skinning the hand. Both heads of the flexor pollicis brevis are covered by the abductor pollicis. Right: Abductor pollicis and opponens pollicis are completely removed. The the deep head of the flexor pollicis brevis is shown with two heads attaching onto the ulnar and radial side at the base of the proximal phalanx of the thumb. The superficial head of the flexor pollicis brevis (dark orange) has a single head that inserts ulnarward onto the proximal phalanx of the thumb.

Bones of the hand and wrist

Names

• Thumb
• First Digit

General

• Regarded as the first digit of the hand
• Functions separately from the other fingers
• Greater range of motion than other fingers

Bones

• First metacarpal
• Proximal Phalanx
• Distal Phalanx

Carpometacarpal Joint

• Greatest range of motion of the thumb
• Movements: flex, extend, abduct, adduct, oppose, and retropulse

Interphalangeal Joint

• Movements: flexion and extension

Movement

• Flexion: occurs in the plane parallel to the palm; the thumb moves into the palm
  • Degrees: 80 degrees at IPJ, 55 at MCPJ, 35 at CMCJ
• Abduction: perpendicular to the palm; the thumb moves away from the palm
  • Degrees: 60
• Opposition: combination of abduction, rotation, and flexion
  • Occurs as the thumb tip is brought to the tip of the little fingеr
• Retropulsion: movement of the thumb dorsally beyond its natural resting position
• Hyperextension: 10-15 degrees

Extrinsic Muscles

• Flexor pollicis longus: primarily responsible for IP flexion
• Abductor pollicis longus: responsible for CMC abduction, extension
• Extensor pollicis brevis: assists with MCP and CMC extension
• Extensor pollicis longus: contributes to MCP and IP extension

Intrinsic Muscles

• Thenar Muscles
  • Muscles: abductor pollicis brevis, flexor pollicis brevis opponens pollicis
  • Responsible for flexion, abduction, and opposition of the thumb.
• Adductor Pollicis: responsible for adduction and opposition

Innervation

• Median Nerve: most muscles of the thumb
• Ulnar Nerve: adductor pollicis, deep head of the flexor pollicis brevis

Vascular

• Deep Palmer Arch
  • Princeps pollicis artery

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Clinical Significance

Traumatic/ Bony

• Rolando Fracture
• Bennett Fracture

Tendon/ Ligament

• De Quervains Tenosynovitis
• Gamekeepers Thumb (UCL)
• Radial Collateral Ligament of the Thumb Injury (RCL)

Arthropathies

• Carpometacarpal Arthritis

Nail Bed Injuries

• Nail Bed Lacerations
• Nail Bed Avulsions
• Subungual Hematoma
• Paronychia
• Felon

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See Also

• Finger Pain Main
• Physical Exam Finger
• Hand Anatomy Main

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