Forearm Anatomy and Function

The Forearm

• The forearm is the distal unit of the upper limb, extending from the elbow to the wrist.
• It contains two bones: the radius and ulna, connected by an interosseous membrane.
• The forearm is divided into anterior and posterior compartments separated by intermuscular septa and the interosseous membrane.

Facial Compartments of Forearm

• The forearm's compartments are divided by intermuscular septa and the interosseous membrane, separating the anterior and posterior compartments.

Anterior Compartment

• Muscles: Includes flexors and pronators.
• Blood Vessels: Ulnar and radial arteries.
• Nerves: Median and ulnar nerves.
• The muscles in the anterior compartment are arranged in three layers: superficial, intermediate, and deep. The muscles in each layer are involved in wrist movements, finger flexion, and pronation.

Muscles of the Anterior Compartment

• The muscles are responsible for wrist joint movements, finger flexion, and pronation.
• They're organised into a superficial, intermediate, and deep layer.

Superficial Layer

• Muscles: Pronator teres, flexor carpi radialis, palmaris longus, and flexor carpi ulnaris. These are the four muscles of the superficial layer.
• Associated actions: pronation, flexion of the wrist and hand.

Intermediate Layer

• Muscle: Flexor digitorum superficialis (FDS). One muscle in the intermediate layer.

Deep Layer

• Muscles: Flexor digitorum profundus, flexor pollicis longus, and pronator quadratus. These three muscles make up the deep layer.

Blood Vessels

• The main arteries in the forearm are the radial and ulnar arteries.
• The arteries pass distally and supply blood to the hand.
• These arteries branch into smaller vessels that also supply the posterior compartment.
• The terminal branches of the brachial artery in the cubital fossa (elbow pit) are the ulnar and radial arteries.

Ulnar Artery

• The ulnar artery is a larger branch of the brachial artery.
• It sits deep to pronator teres, flexor carpi radialis, and flexor digitorum superficialis.

Branches of Ulnar Artery

• Anterior and posterior recurrent arteries
• Common interosseous artery
• Cutaneous branches
• Muscular branches
• Dorsal and palmar carpal branches that supply the wrist.

Radial Artery

• The radial artery is smaller than the ulnar artery
• It lies deep to the brachioradialis in the proximal half of the forearm.
• In the middle third of the forearm, it is lateral to the superficial branch of the radial nerve.
• It is covered by deep fascia and skin in the distal forearm.

Branches of Radial Artery

• Radial recurrent artery
• Cutaneous branches
• Muscular branches
• Palmar carpal branch
• Superficial palmar branch.

Veins of the Forearm

• Superficial veins: Basilic vein, cephalic vein, median vein
• Deep veins: form venae comitantes (companion veins); ulnar vein and radial vein. Deep veins follow the course of deep arteries.

Median Nerve

• The median nerve is the primary nerve of the anterior forearm.
• It supplies all the muscles in the anterior compartment, except the flexor carpi ulnaris (FCU) and the medial half of the flexor digitorum profundus (FDP).
• It has a straight linear course

Branches of Median Nerve

• Anterior interosseous nerve
• Articular branch
• Muscular branches
• Palmar cutaneous branch

Ulnar Nerve

• The ulnar nerve enters the anterior compartment posteriorly around the medial epicondyle of the humerus and between the humeral and ulnar heads of the flexor carpi ulnaris muscle (FCU).
• It supplies only FCU and the ulnar half of the FDP.

Branches of Ulnar Nerve

• Muscular branches
• Two cutaneous branches to the hand (palmar and dorsal)
• Articular branch to the elbow.

Posterior Compartment

• Muscles: Extensors of wrist joint and supinator of forearm
• Blood Vessels: Radial artery branches, anterior interosseous artery, and posterior interosseous artery.
• Nerves: Radial nerve.

Muscles of the Posterior Compartment - Superficial Layer

• Muscles: Brachioradialis, extensor carpi radialis longus, extensor carpi radialis brevis, extensor digitorum, extensor digiti minimi, extensor carpi ulnaris, anconeus.

Muscles of the Posterior Compartment - Deep Layer

• Muscles: Supinator, abductor pollicis longus, extensor pollicis brevis, extensor pollicis longus, extensor indicis. These are the deep layer muscles.

Blood Vessels of the Posterior Compartment

• Posterior Interosseous Artery: Enters the posterior compartment over the proximal margin of the interosseous membrane and gives rise to recurrent interosseous artery. It terminates by joining the dorsal carpal arch of the wrist.
• Anterior Interosseous Artery: Has perforating branches that pass directly through the interosseous membrane to supply deep muscles of the posterior compartment.
• Radial Artery: Has branches which contribute to the supply of the extensor muscles on the radial side of the forearm.

Radial Nerve

• The radial nerve bifurcates into deep and superficial branches beneath the brachioradialis muscle. The deep branch is mainly motor. The superficial branch is mainly sensory. It innervates the skin of the dorsolateral surface of the hand.