Topic Overview

📘 Facts to Remember – Chapter: Forearm and Hand

General Overview

• The forearm extends from the elbow joint to the wrist and contains 20 muscles divided into anterior (flexor-pronator) and posterior (extensor-supinator) compartments.

• The interosseous membrane binds radius and ulna and transmits forces from hand → forearm → arm.

• All flexors of forearm = median nerve supply (except flexor carpi ulnaris and medial ½ of FDP = ulnar nerve).

• All extensors = radial nerve or its posterior interosseous branch.

Muscles

• Superficial flexors share a common origin from the medial epicondyle (common flexor tendon).

• Superficial extensors share a common origin from the lateral epicondyle (common extensor tendon).

• Brachioradialis – only flexor in extensor compartment.

• Pronator teres & pronator quadratus → main pronators; supinator & biceps → main supinators.

• Flexor digitorum profundus flexes DIP joints; flexor digitorum superficialis → PIP joints.

• Lumbricals & interossei → flex MCP & extend IP joints (“writing position”).

• Thenar muscles → control thumb opposition and precision grip.

• Hypothenar muscles → control movement of little finger.

Tendons and Retinacula

• Flexor retinaculum forms the roof of carpal tunnel, transmitting median nerve + 9 tendons (4 FDS + 4 FDP + 1 FPL).

• Extensor retinaculum prevents “bow-stringing” of extensor tendons; contains 6 compartments with synovial sheaths.

• Palmar aponeurosis provides protective covering for underlying structures and continues into fibrous digital sheaths.

Nerves

• Median nerve: main nerve of anterior forearm and lateral palm.

  • Injury → Ape-hand deformity, hand of benediction.

• Ulnar nerve: chief nerve of hand (supplies most intrinsics).

  • Injury at wrist → Claw hand.

• Radial nerve: entirely motor in forearm and sensory on dorsum of hand.

  • Injury → Wrist drop.

• Posterior interosseous nerve: deep branch of radial; supplies all deep extensors.

• Anterior interosseous nerve: branch of median; supplies FPL, lateral FDP, and pronator quadratus.

Arteries

• Brachial artery → divides into radial and ulnar arteries in cubital fossa.

• Radial artery: mainly forms deep palmar arch.

• Ulnar artery: mainly forms superficial palmar arch.

• Common interosseous artery (from ulnar) → divides into anterior and posterior interosseous arteries.

• Arterial arches ensure collateral flow between radial and ulnar arteries.

Venous and Lymphatic Drainage

• Superficial veins: cephalic (lateral) and basilic (medial) → connected by median cubital vein.

• Deep veins: venae comitantes accompany arteries.

• Lymphatics:

  • Palmar → follow deep veins → axillary nodes.

  • Dorsal → follow superficial veins → cubital then axillary nodes.

Important Anatomical Relations

• Radial artery pulse: lateral to flexor carpi radialis tendon.

• Ulnar artery pulse: lateral to pisiform bone.

• Median nerve at wrist: lies beneath flexor retinaculum → compressed in carpal tunnel.

• Ulnar nerve & artery: pass superficial to retinaculum through Guyon’s canal.

• Radial nerve & artery: cross the anatomical snuffbox.

Fascial Spaces & Synovial Sheaths

• Thenar space → lateral palm (thumb, index).

• Mid-palmar space → medial palm (middle & ring fingers).

• Pulp space → fingertips (site of whitlow).

• Parona’s space → forearm; communicates with thenar & mid-palmar spaces.

• Ulnar bursa → sheath for FDS & FDP.

• Radial bursa → sheath for FPL.

Clinical Points

• Tennis elbow: inflammation of common extensor origin.

• Golfer’s elbow: inflammation of common flexor origin.

• Carpal tunnel syndrome: compression of median nerve beneath flexor retinaculum.

• Guyon’s canal syndrome: compression of ulnar nerve superficial to retinaculum.

• De Quervain’s disease: tenosynovitis of APL & EPB (first dorsal compartment).

• Mallet finger: rupture of extensor tendon at DIP joint.

• Dupuytren’s contracture: fibrosis of palmar aponeurosis → flexion of fingers.

• Claw hand: ulnar nerve lesion.

• Ape hand: median nerve lesion in thenar region.

• Wrist drop: radial nerve palsy.

• Hand of Benediction: median nerve lesion at elbow.

Palmar Arches

• Superficial palmar arch: mainly ulnar; level = distal border of thumb.

• Deep palmar arch: mainly radial; level = proximal border of thumb.

• Allen’s test checks collateral flow between them.

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