What are the intrinsic muscles for digits 2, 3, and 4?

Intrinsic Muscles of Digits 2,3, and 4

The intrinsic muscles of digits 2,3, and 4 (index, middle, and ring fingers) include the dorsal interossei, palmar interossei, and lumbrical muscles, which collectively control fine motor movements of these fingers.

Dorsal Interossei Muscles

• Four dorsal interossei muscles are present in the hand, positioned between the metacarpal bones:

  • First dorsal interosseous: Located between thumb and index finger metacarpals
  • Second dorsal interosseous: Between index and middle finger metacarpals
  • Third dorsal interosseous: Between middle and ring finger metacarpals
  • Fourth dorsal interosseous: Between ring and little finger metacarpals

• Primary functions of dorsal interossei:

  • Abduction of fingers (spreading fingers apart)
  • Flexion of metacarpophalangeal (MCP) joints
  • Extension of interphalangeal (IP) joints 1

Palmar Interossei Muscles

• Three palmar interossei muscles are traditionally described (though some research indicates a fourth palmar interosseous associated with the thumb in 91% of hands) 2:

  • First palmar interosseous: Located on the ulnar side of the index finger
  • Second palmar interosseous: Located on the radial side of the ring finger
  • Third palmar interosseous: Located on the radial side of the little finger

• Primary functions of palmar interossei:

  • Adduction of fingers (bringing fingers together)
  • Flexion of MCP joints
  • Extension of IP joints 3

Lumbrical Muscles

• Four lumbrical muscles originate from the flexor digitorum profundus (FDP) tendons in the palm:

  • First lumbrical: Inserts on the radial side of index finger
  • Second lumbrical: Inserts on the radial side of middle finger
  • Third lumbrical: Inserts on the radial side of ring finger
  • Fourth lumbrical: Inserts on the radial side of little finger

• Primary functions of lumbricals:

  • Flexion of MCP joints
  • Extension of IP joints
  • Fine coordination of finger movements 4

Clinical Significance

• The intrinsic muscles work in coordination with extrinsic muscles (like flexor digitorum profundus) to produce precise finger movements and grip strength 5

• Dysfunction of these muscles can lead to conditions such as:

  • Intrinsic plus hand: A painful contracture with excessive flexion at the MCP joints and extension at the IP joints 6
  • Referred pain patterns: Pain in the third and fourth dorsal interossei can mimic C7 or C8 radiculopathies or ulnar neuropathy 3

• The strength of common neural input is stronger within individual intrinsic muscles than between different intrinsic muscles, suggesting specialized control for different functional roles in grasping 1

Anatomical Relationships

• These intrinsic muscles are innervated by the deep branch of the ulnar nerve, except for the first and second lumbricals which are innervated by the median nerve

• The intrinsic muscles work in coordination with extrinsic muscles to produce different types of grip, with the FDP tendon being essential for power grip, precision grip, hook grip, and pinch grip 4

Understanding these intrinsic muscles is crucial for diagnosing and treating hand disorders, as they are essential for the fine motor control that distinguishes human hand function.