Anatomy of the Forearm Flexors

Flexor Aspect of Forearm

• Superficial Fascia: Continuation of the deep fascia of the arm, thickens to form the flexor retinaculum at the wrist.

Flexor Retinaculum

• Distal Row: Located on the distal row of carpal bones.
• Proximal Row: Located on the proximal row of carpal bones.
• Floor of the Anatomical Snuff Box: Forms the floor of the anatomical snuff box.

Cutaneous Innervation

• Medial Cutaneous Nerve of Forearm: Innervates the medial aspect of the forearm
• Lateral Cutaneous Nerve of Forearm: Innervates the lateral aspect of the forearm

Superficial Veins

Palmar Aspect

• Palmar Digital Veins: Begin as palmar digital veins and communicate with dorsal veins.
• Median Vein of the Forearm: Drains into the superficial palmar plexus, which begins the median vein of the forearm.

Dorsal Aspect

• Dorsal Digital Veins: Begin as dorsal digital veins and are joined by oblique veins.
• Dorsal Metacarpal Veins: Unite to form three dorsal metacarpal veins on the dorsum of the hand.
• Dorsal Venous Network: Dorsal metacarpal veins eventually form the dorsal venous network.
• Cephalic Vein: Emerges from the lateral aspect of the dorsal venous network.
• Basilic Vein: Emerges from the medial aspect of the dorsal venous network.

Common Flexor Tendon:

• Origin: Medial epicondyle of the humerus.

Muscles:

Superficial Group

• Pronator Teres:

  • Origin: Humeral head (medial epicondyle) and ulnar head (coronoid process).
  • Insertion: Middle part of the lateral surface of the radius.
  • Nerve: Median nerve.
  • Function: Pronates and flexes the forearm.

• Flexor Carpi Radialis:

  • Origin: Medial epicondyle.
  • Insertion: Bases of the 2nd and 3rd metacarpals.
  • Nerve: Median nerve.
  • Function: Flexes and abducts the hand.

• Palmaris Longus:

  • Origin: Medial epicondyle.
  • Insertion: Palmar aponeurosis.
  • Nerve: Median nerve.
  • Function: Flexes the hand and tightens the palmar aponeurosis.
  • Tendon: Passes superficial to the flexor retinaculum.

• Flexor Carpi Ulnaris:

  • Origin: Humeral head (medial epicondyle) and ulnar head (olecranon, posterior border of ulna).
  • Insertion: Pisiform bone, hook of hamate, base of the 5th metacarpal bone.
  • Nerve: Ulnar nerve.
  • Function: Flexion and adduction of the hand.

Middle Group

• Flexor Digitorum Superficialis:
  • Origin: Humeroulnar head (medial epicondyle, ulnar collateral ligament, coronoid process of ulna) and radial head (anterior part of radius).
  • Insertion: Bases of the middle phalanges of the 2nd-5th digits.
  • Nerve: Median nerve.
  • Function: Flexion of the middle phalanges of the 2nd-5th digits at the proximal interphalangeal joints and flexion of the hand.
  • Tendon: Each tendon divides into two slips at the level of the proximal phalanges, inserting to the lateral sides of the middle phalanges on both sides.

Deep Group

• Flexor Digitorum Profundus:

  • Origin: Anterior surface of the ulna and interosseous membrane.
  • Insertion: Distal phalanges of the 2nd-5th digits.
  • Nerve: Medial part (4th & 5th digits) by ulnar nerve; lateral part (2nd & 3rd digits) by the anterior interosseous nerve from the median nerve.
  • Function: Flexion of the distal phalanges of the 2nd-5th digits and flexion of the hand.

• Flexor Pollicis Longus:

  • Origin: Anterior surface of the radius and interosseous membrane.
  • Insertion: Distal phalanx of the thumb.
  • Nerve: Anterior interosseous nerve (median nerve).
  • Function: Flexes the thumb.

• Pronator Quadratus:

  • Origin: Anterior surface of the ulna.
  • Insertion: Distal part of the anterior surface of the radius.
  • Nerve: Anterior interosseous nerve (median nerve).
  • Function: Main pronator of the forearm.
  • Pronator Teres: Pronator Teres assists in rapid pronation of the forearm.

Cubital Fossa

• Base: Line connecting the medial and lateral epicondyle.
• Medial: Pronator Teres muscle.
• Lateral: Brachioradialis muscle.
• Floor: Brachialis and supinator muscles.

Contents of Cubital Fossa:

• Median Cubital Vein: Located superficially.
• Tendon of Biceps Brachii Muscle: Located lateral to the brachial artery and median nerve.
• Brachial Artery: Located medial to the biceps tendon and lateral to the median nerve.
• Median Nerve: Located medial to the brachial artery.

Arteries of the Forearm

Ulnar Artery

• Branches:
  • Anterior Ulnar Recurrent Artery
  • Posterior Ulnar Recurrent Artery
  • Common Interosseous Artery
    • Anterior Interosseous Artery
    • Posterior Interosseous Artery
  • Palmar Carpal Artery
  • Dorsal Carpal Artery
  • Deep Palmar Artery

Radial Artery

• Location: Deep to brachioradialis muscle proximally.

• Distal End: Only covered by superficial fascia and deep fascia distally, making pulsations palpable.

• Branches:

  • Recurrent Radial Artery
  • Superficial Palmar Branch
  • Palmar Carpal Branch
  • Dorsal Carpal Branch
    • Dorsal Metacarpal Branches
    • Dorsal Digital Branches
  • Princeps Pollicis Artery
  • Radialis Indicis Artery

Palmar Arches

• Deep Palmar Arch: Formed by the radial artery.
• Superficial Palmar Arch: Formed by the ulnar artery.

Synovial Sheaths of the Long Flexor Tendons

• These sheaths provide lubrication and reduce friction during tendon movement.

Carpal Tunnel

• Location: A narrow passageway at the wrist formed by the carpal bones and the flexor retinaculum.
• Contents: Tendon of the flexor digitorum superficialis, tendon of the flexor digitorum profundus, tendon of the flexor pollicis longus, and the median nerve.

Carpal Tunnel Syndrome

• Cause: Any lesion reducing the size of the carpal tunnel can cause compression of the median nerve.
• Symptoms: Pain, numbness, and tingling in the hand (especially in the thumb, index, middle, and radial half of the ring finger).
• Palmar Cutaneous Branch: Usually not affected because it runs superficial to the flexor retinaculum.