Forearm Anatomy and Fascia Structure

Forearm Anatomy and Function

• Forearm plays a crucial role in temperature regulation.
• Damage, such as scarring from burns or poorly placed incisions, especially after deep axilla burns, has severe consequences.

Fascia Structure and Function

• Superficial fascia is thicker on the dorsal part of the neck, shoulder, arm, and forearm. Arm thickness is a measure of obesity.
• It acts as a gliding plane between skin and deep fascia.
• Nerves and vessels risk entrapment or rupture when penetrating deep fascia.
• Deep fascia, intermuscular septa, and interosseous membrane create compartments, facilitating structure gliding and muscle attachment.

Fascial Compartments and Clinical Significance

• Fascial compartments are vital in infection and tumor spread, crucial in ischaemia (reduced blood flow).
• Prevertebral fascia surrounds crucial structures like phrenic nerve, scalene muscles, cervical rami, and vessels.
• It extends below the clavicle as axillary sheath, encompassing brachial plexus and axillary artery, and continuing as brachial sheath.
• Shoulder and axilla muscles (deltoid, pectoralis major, latissimus dorsi) have deep fascia that blends with arm deep fascia.
• This arrangement forms the cone-shaped axillary space.

Deep Fascia of the Arm and Forearm

• The arm and forearm deep fascia act as a sleeve.
• It attaches to intermuscular septa, epicondyles, olecranon, and ulna/radius periosteum.
• Important condensations include bicipital aponeurosis, flexor and extensor retinacula and septa.
• Forearm's discrete compartments separate superficial and deep muscles.
• Extensor muscles (brachioradialis, radial extensors) form a 'mobile wad' overlying the deeper compartment with interosseous nerve, vessels, supinator, digital extensors etc.

Forearm Compartments

• Anterior forearm has three compartments.
• Deep flexor compartment houses anterior interosseous nerve and vessels, flexor pollicis longus, flexor digitorum profundus, and pronator quadratus.
• Superficial compartment contains radial artery, pronator teres, flexor carpi radialis, palmaris longus, and flexor digitorum superficialis.
• Ulnar nerve and vessels lie in a separate sheath near the ulna.

Forearm Fascia and Hand

• Forearm's anterior deep fascia connects to palmar aponeurosis, forming the hand's fibrous skeleton (using a septal arrangement).

Nerve Mobility

• Upper limb main nerves exhibit 10-15 mm excursion across fixed points (first rib, distal humerus, distal radius).
• Gliding occurs between adventitia-epineurium, epineurium-perineurium, and perineurium itself layers.

Cutaneous Innervation

• Nerve bundles enter deep dermis and proceed towards surface, branching into unmyelinated axons innervating end organs.
• Myelinated axons connect to hair follicles, Meissner corpuscles, and Merkel complexes.
• Epidermal innervation density is highest proximally and remains consistent with age.

Muscles and Movement

• Sensorimotor cortex controls movement, not individual muscles.
• Complex movement like catching a ball requires integrated action of multiple upper limb muscle groups (as well as potentially other body parts).