Anterior Compartment of the Forearm

The anterior compartment of the forearm is also known as the flexor-pronator compartment. It contains muscles primarily responsible for flexion of the wrist and fingers as well as pronation of the forearm. The compartment is bordered by the antebrachial fascia and is separated from the posterior compartment by the interosseous membrane and intermuscular septa.

Boundaries

Structure	Description
Anterior	Skin and superficial fascia
Posterior	Radius, ulna, interosseous membrane
Medial & Lateral	Intermuscular septa, medial and lateral borders of forearm

Muscle Layers

The anterior compartment has three layers: superficial, intermediate, and deep.

Superficial Layer (5 Muscles)

Muscle	Origin	Insertion	Innervation	Function
Pronator teres	Medial epicondyle & coronoid process of ulna	Lateral surface of radius	Median nerve	Forearm pronation, weak elbow flexion
Flexor carpi radialis	Medial epicondyle	Base of 2nd and 3rd metacarpals	Median nerve	Flexion and radial deviation of wrist
Palmaris longus	Medial epicondyle	Palmar aponeurosis	Median nerve	Wrist flexion; tenses palmar fascia
Flexor carpi ulnaris	Medial epicondyle & olecranon	Pisiform, hook of hamate, base of 5th metacarpal	Ulnar nerve	Flexion and ulnar deviation of wrist
Flexor digitorum superficialis (also considered intermediate)	Medial epicondyle, radius	Middle phalanges of digits 2–5	Median nerve	Flexion at PIP joints and MCP joints

Deep Layer (3 Muscles)

Muscle	Origin	Insertion	Innervation	Function
Flexor digitorum profundus	Ulna and interosseous membrane	Distal phalanges of digits 2–5	Medial half: ulnar nerve Lateral half: median nerve (AIN)	Flexion at DIP joints
Flexor pollicis longus	Radius and interosseous membrane	Distal phalanx of thumb	Median nerve (anterior interosseous nerve)	Flexion of thumb at IP joint
Pronator quadratus	Distal ulna	Distal radius	Median nerve (AIN)	Forearm pronation

Contents

• Median nerve: Supplies most muscles; travels between FDS and FDP
• Ulnar nerve: Supplies FCU and medial half of FDP; travels medially with ulnar artery
• Radial and ulnar arteries: Main blood supply to muscles
• Anterior interosseous nerve and artery: Supply deep muscles

Function

• Flexion: Of wrist, MCP, PIP, and DIP joints
• Pronation: Of the forearm by pronator teres and pronator quadratus
• Grip assistance: Through coordinated flexor action during grasping

Blood Supply

• Ulnar artery: Primary source for superficial and deep branches
• Radial artery: Contributes to lateral side
• Anterior interosseous artery: Deep muscle supply

Innervation

• Median nerve: All muscles except FCU and medial FDP
• Ulnar nerve: FCU and medial (ulnar) half of FDP

Surface Anatomy

The tendons of FDS and FCR become prominent in the distal forearm and at the wrist crease. The palmaris longus (if present) is visible during wrist flexion.

Clinical Significance

• Pronator syndrome: Compression of median nerve between heads of pronator teres
• Anterior interosseous syndrome: Isolated motor neuropathy causing inability to make the “OK” sign
• Compartment syndrome: Deep fascia limits expansion, requiring fasciotomy in severe swelling
• Tendonitis: Overuse of flexor tendons can lead to medial epicondylitis ("golfer's elbow")

Comparative Anatomy

In quadrupeds, the flexor compartment supports locomotion. In humans, it has evolved for fine control of hand and finger movement essential for precision tasks like writing, typing, and tool use.