Intrinsic Muscles of the Hand

Hypothenar Muscles

• Origin: Carpal bones and flexor retinaculum
  • Abductor Digiti Minimi (ADM)
  • Action: ABduction of digit V and Flexion of digit V at the Metacarpophalangeal (MCP) joint
  • Innervation: Ulnar Nerve
  • Flexor Digiti Minimi Brevis (FDMB)
  • Action: Flexion of digit V at the MCP and Proximal Interphalangeal (PIP) joints
  • Innervation: Ulnar Nerve
  • Opponens Digiti Minimi (ODM)
  • Action: Oppose digit V slightly
  • Innervation: Ulnar Nerve

Adductor Pollicis

• Origin: Metacarpals II and III
• Action: ADduction of digit I (thumb)
• Innervation: Ulnar Nerve

Interosseous Muscles

• Origin: Metacarpals
  • Palmar Interossei (PI)
  • Action: ADduction of digits II, IV, and V
  • Innervation: Ulnar Nerve
  • Dorsal Interossei (DI)
  • Action: ABduction of digits II, IV, and V
  • Innervation: Ulnar Nerve

Lumbricals

• Origin: Tendons of the flexor digitorum profundus
• Action: MCP flexion with PIP and DIP (distal interphalangeal) extension, also known as the “intrinsic plus” position
• Innervation:
  • Digits II and III: Median Nerve
  • Digits IV and V: Ulnar Nerve