Muscle Compartments of the Upper Limb

The upper limb is divided into distinct muscle compartments by deep fascia, intermuscular septa, and bones. These compartments house functionally related muscles, along with their associated nerves and blood vessels. Compartmentalization allows for coordinated movement, efficient neurovascular routing, and containment of infections or pressure-related conditions.

1. Arm (Brachium) Compartments

The arm is divided into two main compartments by the medial and lateral intermuscular septa:

Anterior Compartment (Flexor Compartment)

• Muscles: Biceps brachii, Brachialis, Coracobrachialis
• Function: Flexion of the elbow and shoulder; supination of the forearm (biceps)
• Innervation: Musculocutaneous nerve (C5–C7)
• Blood Supply: Brachial artery and its muscular branches

Posterior Compartment (Extensor Compartment)

• Muscles: Triceps brachii, Anconeus
• Function: Extension of the elbow and shoulder
• Innervation: Radial nerve (C6–C8)
• Blood Supply: Deep brachial artery (profunda brachii)

2. Forearm (Antebrachium) Compartments

The antebrachial fascia and interosseous membrane divide the forearm into two main compartments:

Anterior Compartment (Flexor-Pronator Compartment)

• Superficial Muscles: Pronator teres, Flexor carpi radialis, Palmaris longus, Flexor carpi ulnaris
• Intermediate Muscle: Flexor digitorum superficialis
• Deep Muscles: Flexor digitorum profundus, Flexor pollicis longus, Pronator quadratus
• Function: Flexion of wrist and fingers, forearm pronation
• Innervation: Median nerve (main); ulnar nerve (medial part of FDP and FCU)
• Blood Supply: Ulnar and radial arteries, anterior interosseous artery

Posterior Compartment (Extensor-Supinator Compartment)

• Superficial Muscles: Brachioradialis, Extensor carpi radialis longus & brevis, Extensor digitorum, Extensor digiti minimi, Extensor carpi ulnaris
• Deep Muscles: Supinator, Abductor pollicis longus, Extensor pollicis brevis & longus, Extensor indicis
• Function: Extension of wrist, fingers, and thumb; forearm supination
• Innervation: Radial nerve (deep branch → posterior interosseous nerve)
• Blood Supply: Posterior interosseous artery

3. Hand Compartments

The hand is organized into several functional compartments:

Thenar Compartment

• Muscles: Abductor pollicis brevis, Flexor pollicis brevis, Opponens pollicis
• Innervation: Recurrent branch of median nerve
• Function: Thumb movement (abduction, flexion, opposition)

Hypothenar Compartment

• Muscles: Abductor digiti minimi, Flexor digiti minimi brevis, Opponens digiti minimi
• Innervation: Deep branch of ulnar nerve
• Function: Movement of the fifth digit

Central Compartment

• Muscles: Lumbricals
• Tendons: Flexor digitorum superficialis and profundus
• Innervation: Median nerve (lateral 2 lumbricals), Ulnar nerve (medial 2 lumbricals)
• Function: MCP flexion and IP extension

Adductor Compartment

• Muscle: Adductor pollicis
• Innervation: Deep branch of ulnar nerve
• Function: Thumb adduction

Interosseous Compartments

• Muscles: Palmar and dorsal interossei
• Innervation: Deep branch of ulnar nerve
• Function: Finger adduction (palmar) and abduction (dorsal), assist lumbricals

Clinical Significance

• Compartment Syndrome: Raised pressure within a muscle compartment (commonly forearm) can lead to ischemia and nerve damage; requires prompt fasciotomy.
• Nerve Injury Diagnosis: Patterns of muscle weakness or atrophy can help localize nerve damage to specific compartments.
• Surgical Planning: Knowledge of compartments is crucial in trauma, reconstructive surgery, and targeted nerve blocks.

Comparative Anatomy

In non-human primates, compartmentalization is present but less refined. In humans, the complexity and separation of compartments reflect the advanced motor control required for tool use, writing, and precise hand function.