Upper Limb Part 3

Overview of the Intrinsic Hand Musculature

  • Distinction between intrinsic and extrinsic hand muscles

    • Extrinsic hand muscles originate in the forearm (antebrachium)

    • Intrinsic hand muscles originate in the hand itself

1. Thenar Muscles of the Thumb

A. Abductor Pollicis

  • Orientation: Positioned on the palmar (ventral) side of the thumb

  • Action: Abduction of the thumb

    • Pulls the thumb away from the palm during shortening

    • Important muscle for thumb movement and function

  • Topography:

    • Located superficially; can be felt easily on the palmar side of the hand

B. Opponens Pollicis

  • Orientation & Function:

    • Muscles fibers are oriented obliquely, allowing for inward swinging action towards the palm

    • Important for opposition of the thumb, which is a key movement for grasping objects

  • Depth:

    • Located deeper than the abductor pollicis and flexor pollicis brevis

    • Only visible in certain diagrams of the paw, specifically on the radial side

C. Adductor Pollicis

  • Action:

    • Adduction of the thumb, which means bringing the thumb towards the base of the other fingers

    • Starts from abducted position of the thumb

  • Orientation:

    • Muscle belly located between the metacarpals of the thumb and index finger

    • Contains two distinct parts: a transverse head and an oblique head

    • Oblique head is angled, while transverse head runs straight across

    • Overall shape resembles a flipped number seven, useful for memorization

2. Intermetacarpal Muscles

A. Lumbricals

  • Etymology: Derived from Latin, meaning "little worms" due to their shape

  • Origin: Attach to tendons of the flexor digitorum profundus

  • Function:

    • Cross the metacarpophalangeal (MCP) joints on the palmar side and are responsible for flexion of the MCP joints

    • Extend the proximal interphalangeal (PIP) and distal interphalangeal (DIP) joints

  • Topography: Very superficial, beneath the palmar aponeurosis

B. Palmar Interossei

  • Name Origin: "Interossei" means between the bones, specifically between metacarpals

  • Location: Closer to the palmar surface than dorsal interossei

  • Function:

    • Responsible for adduction of the fingers towards the middle finger (PAD: Palmar ADductor)

    • Attach near the MCP joints and extend into the extensor expansion, thus facilitating extension of IP joints when the palmar interossei contract

  • Depth: Deep in anatomical position between the metacarpal bones

C. Dorsal Interossei

  • Function:

    • Abduct the fingers away from the midline of the hand (DAB: Dorsal ABductor)

    • Contribute to extension of the proximal and distal interphalangeal joints via attachment to the extensor expansion

  • Location:

    • Two dorsal interossei are present on the middle finger, as it serves as a midline reference point

    • None exists for the little finger, which has its separate abductor muscle

3. Extensor Expansion

  • Definition: A complex structure on the dorsal side of the hand, formed by intrinsic muscles and contributing tendons that extend the fingers

  • Group Associations:

    • Six intrinsic muscles attach and contribute to the extensor expansion (3 extrinsic and 3 intrinsic)

  • Extrinsic Muscles Involved:

    • Extensor digitorum

    • Extensor digiti minimi

    • Extensor indicis

  • Intrinsic Muscles Involved:

    • Lumbricals

    • Palmar interossei

    • Dorsal interossei

4. Carpal Tunnel and Compression Syndromes

  • Anatomy:

    • Comprised of carpal bones dorsally and transverse carpal ligament palmar side

    • Contains nine flexor tendons (flexor digitorum superficialis and profundus) and the median nerve

  • Pathophysiology:

    • Repetitive motion can lead to swelling and increased pressure in the canal, resulting in median nerve compression (carpal tunnel syndrome)

  • Symptoms:

    • Numbness, tingling, weakness, and pain in the hand

  • Surgical Treatment:

    • Carpal ligament may be cut to relieve pressure, with a high success rate (90-95%)

5. Anatomical Snuff Box

  • Definition: A depression on the lateral aspect of the wrist

  • Formed By:

    • Tendons of extensor pollicis brevis and abductor pollicis longus on one side

    • Tendon of extensor pollicis longus on the other

  • Clinical Relevance:

    • Contains the radial artery's deep branch, important in surgical procedures

    • Can be used for accessing vessels and determining pulse points

6. Vascular Supply of the Hand

  • Major Arteries:

    • Radial and ulnar arteries branch into:

    • Superficial palmar arch (serves palmar hand)

    • Deep palmar arch (serves dorsal muscles)

  • Procedure:

    • Identification of arteries serving specific muscles or regions based on their innervation provided to hands

7. Brachial Plexus

  • Mnemonic: Aids memorization of brachial plexus anatomy:

    • "You young mermaids line them up in front of Poseidon's ultra trident. LSD salt may many mermaids undergo mass misery, and Robert Taylor drinks cold beer"

  • Structure:

    • Divided into roots, trunks, divisions, cords, and branches

    • Understand contributions from spinal levels for effective clinical applications

Conclusion

  • Review Strategy: Utilize comprehensive images and diagrams in studies to associate muscle functions and identify specific groups. Ensure familiarity with relationships of arteries, veins, and nerve pathways in the hand.

  • Class Exercises: Draw the brachial plexus and study the anatomy of individual digits to strengthen anatomical knowledge and application in practical scenarios.