Topic Overview

Muscles of the Front of Forearm 

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Overview

• The anterior compartment of the forearm contains flexor and pronator muscles.

• These muscles are arranged in three layers:

  1. Superficial group

  2. Intermediate group (Flexor digitorum superficialis)

  3. Deep group

• Common origin: Medial epicondyle of humerus via the common flexor tendon.

• Nerve supply: Mostly median nerve (C6–C8), except flexor carpi ulnaris and medial half of flexor digitorum profundus (ulnar nerve).

• Main actions: Flexion of wrist and digits, pronation of forearm.

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I. Superficial Muscles 

👉 Mnemonic: “Pass–Fail–Pass–Fail” (from lateral to medial)
P – Pronator teres
F – Flexor carpi radialis
P – Palmaris longus
F – Flexor carpi ulnaris

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1. Pronator Teres

Origin

• Humeral head: Medial supracondylar ridge and common flexor origin.

• Ulnar head: Medial side of coronoid process of ulna.

Insertion

• Middle of lateral surface of radius.

Nerve Supply

• Median nerve (C6–C7).

Action

• Pronates forearm and assists in elbow flexion.

Clinical Note

• Median nerve passes between its two heads → compression here causes pronator syndrome.

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2. Flexor Carpi Radialis

Origin

• Common flexor origin from medial epicondyle of humerus.

Insertion

• Bases of 2nd and 3rd metacarpal bones.

Nerve Supply

• Median nerve (C6–C7).

Action

• Flexes and abducts wrist (radial deviation).

Clinical Note

• Used as a guide to locate radial artery pulse (artery lies lateral to its tendon).

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3. Palmaris Longus

Origin

• Common flexor origin (medial epicondyle).

Insertion

• Flexor retinaculum and palmar aponeurosis.

Nerve Supply

• Median nerve (C7–C8).

Action

• Tenses palmar fascia and flexes wrist.

Clinical Note

• Absent in about 10–15% of individuals; used for tendon grafts.

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4. Flexor Carpi Ulnaris

Origin

• Humeral head: Medial epicondyle of humerus.

• Ulnar head: Olecranon and posterior border of ulna.

Insertion

• Pisiform, hook of hamate, and base of 5th metacarpal.

Nerve Supply

• Ulnar nerve (C7–C8).

Action

• Flexes and adducts wrist (ulnar deviation).

Clinical Note

• Only superficial forearm flexor supplied by ulnar nerve.

• Forms the roof of ulnar nerve groove at wrist.

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II. Intermediate Muscle

Flexor Digitorum Superficialis

Origin

• Humeroulnar head: Medial epicondyle, ulnar collateral ligament, coronoid process.

• Radial head: Oblique line of radius.

Insertion

• By four tendons into the middle phalanges of medial four fingers (each splits into two slips at PIP joint).

Nerve Supply

• Median nerve (C7–T1).

Action

• Flexes proximal interphalangeal joints (PIP), also assists in wrist and MCP flexion.

Clinical Note

• Important test: isolate PIP joint movement while immobilizing others → tests FDS integrity.

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III. Deep Muscles 

👉 Mnemonic: “F–F–P”

• Flexor digitorum profundus

• Flexor pollicis longus

• Pronator quadratus

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1. Flexor Digitorum Profundus (FDP)

Origin

• Anterior and medial surfaces of ulna and interosseous membrane.

Insertion

• Bases of distal phalanges of medial four fingers.

Nerve Supply

• Medial half → Ulnar nerve (C8–T1).

• Lateral half → Anterior interosseous branch of median nerve (C8–T1).

Action

• Flexes distal interphalangeal joints (DIP), assists in flexion of PIP and wrist joints.

Clinical Note

• Test: flex DIP joint while keeping PIP fixed → tests FDP.

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2. Flexor Pollicis Longus

Origin

• Anterior surface of radius and adjacent interosseous membrane.

Insertion

• Base of distal phalanx of thumb.

Nerve Supply

• Anterior interosseous nerve (C8–T1).

Action

• Flexes IP joint of thumb and assists in wrist flexion.

Clinical Note

• Involved in tenosynovitis of thumb (pain during thumb flexion).

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3. Pronator Quadratus

Origin

• Distal fourth of anterior surface of ulna.

Insertion

• Distal fourth of anterior surface of radius.

Nerve Supply

• Anterior interosseous nerve (branch of median nerve).

Action

• Chief pronator of forearm (acts with pronator teres).

• Helps stabilize distal radioulnar joint.

Clinical Note

• Last muscle to be paralyzed in median nerve injury at forearm level.

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Dissection of the Front of Forearm 

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Steps

1. Make a midline incision from elbow to wrist.

2. Reflect the skin and superficial fascia to expose:

   • Median cubital vein (in cubital fossa).

   • Medial & lateral cutaneous nerves of forearm.

3. Remove deep fascia → identify superficial muscles (Pass–Fail–Pass–Fail).

4. Reflect these muscles to expose:

   • Flexor digitorum superficialis → intermediate layer.

   • Beneath it, note the deep muscles (FDP, FPL, Pronator quadratus).

5. Identify median nerve between FDS and FDP; ulnar nerve between FCU and FDP.

6. Observe radial and ulnar arteries with their companion veins.