Lecture on Hand Muscles

Categories of Hand Muscles

• Extrinsic Muscles
  • Origin proximal to the wrist (before the wrist)
  • Insert into the hand
  • Examples: Flexor digitorum superficialis (FDS), Extensor digitorum
• Intrinsic Muscles
  • Origin and insertion entirely within the hand
  • Examples: Lumbricals, Thenar muscle group, Hypothenar muscle group

Finger Flexors

• Extrinsic Finger Flexors
  • Flexor Digitorum Superficialis (FDS)
    • Splits into two tendons at the MCP joint, inserting at the middle phalanges (PIP joint)
    • Responsible for PIP flexion
  • Flexor Digitorum Profundus (FDP)
    • Passes through the split of the FDS tendons, inserting at the distal phalanges (DIP joint)
    • Responsible for DIP flexion
  • Both muscles contribute to MCP flexion

Tendon Ligaments

• Tendons are surrounded by ligaments (annular and cruciate ligaments)
  • Annular Ligaments (A1-A5): Keep tendons close to the bone
  • Cruciate Ligaments: Cross-shaped ligaments
• Pulley System
  • Functions to anchor tendons, maintaining full range of motion
  • Important pulleys: A2 (MCP joint), A4 (PIP joint)

Finger Extensors

• Extrinsic Finger Extensors
  • Extensor Digitorum Communis (EDC)
    • Common extensor for all digits
  • Extensor Digiti Minimi (EDM)
    • Specific for the little finger
  • Extensor Indicis
    • Specific for the index finger

Compartmentalization

• Extensor tendons are divided into six compartments at the wrist
  • First Compartment: Abductor pollicis longus (APL), Extensor pollicis brevis (EPB)
  • Second Compartment: Wrist extensors (Extensor carpi radialis longus & brevis)
  • Third Compartment: Extensor pollicis longus (EPL)
  • Fourth Compartment: Extensor digitorum communis (EDC), Extensor indicis
  • Sixth Compartment: Extensor carpi ulnaris (ECU)

Extensor Hood Mechanism

• Extensor tendons blend into the extensor hood at the MCP joint
• Tendon splits into:
  • Central Slip: Inserts at the middle phalanges (PIP joint)
  • Lateral Bands: Insert at the distal phalanges (DIP joint)
• Extensor hood assists in MCP extension; PIP and DIP extension require additional tissue support

Intrinsic Muscles

• Lumbricals
  • Originates from the flexor digitorum profundus tendons
  • Inserts into the extensor hood
  • Function: MCP flexion, PIP and DIP extension
• Interossei Muscles
  • Palmar Interossei
    • Adduction of the fingers (pulling toward the middle finger)
  • Dorsal Interossei
    • Abduction of the fingers (pulling away from the middle finger)
  • Both assist in MCP flexion and IP extension by joining the extensor hood