This nerve branches from the radial nerve at the level of the radiocapitellar joint and are typically located immediately proximal to the supinator muscle in an area of a fibrous band known as the arcade of Frohse. A motor nerve that branches from the radial nerve is the posterior interosseous nerve. As it travels to the elbow, it innervates the triceps muscle. The radial nerve divides off the posterior cord of the brachial plexus. Once it branches from the ulnar nerve, it travels posterolateral, eventually supplying blood to muscles in the posterior compartment. The posterior interosseous artery is a branch from the ulnar artery. The superficial arch also receives contributions from the superficial branch of the radial artery. In contrast, the superficial palmar arch's predominant blood supply is derived from the ulnar artery. The deep palmar arch derives its main contribution from the deep arterial branch of the radial artery. The radial artery then continues laterally in the forearm, eventually contributing to the superficial and deep palmar arches in the palmar aspect of the hand. Immediately superior to the antecubital fossa, the brachial artery branches into ulnar and radial arteries. It then becomes the brachial artery once it passes the lower edge of the teres minor muscle. As it traverses towards the upper extremity, it becomes the axillary artery at the lateral border of the first rib. The subclavian artery branches off from the aortic arch. Zone II: covers the interphalangeal joint.Zone I: covers the fingertip to the DIP joint.Below is a description of the extensor tendon zones of the thumb: The thumb zones are classified differently from the tip of the thumb to the carpal-metacarpal joint. Zone V: situated at the metacarpal phalangeal (MP) joint.Zone III: located at the proximal interphalangeal (PIP) joint.Zone I: covers the fingertip to the distal interphalangeal (DIP) joint.Below is a description of the extensor tendon zones: Įxtensor tendon zones are a helpful way to identify the region where injuries to the extensor tendons occur in the hand and wrist. Independent small finger extension is accomplished by the extensor digiti minimi (EDM) muscle. Independent index finger extension can be carried out by the extensor indicis proprius (EIP) muscle. When referencing the dorsal aspect of the wrist, the EPB and EPL tendons create the medial and lateral borders of the anatomic snuffbox, respectively.Įxtension of the second (index finger), third (long finger), fourth (ring finger), and fifth (small finger) digits occurs via the extensor digitorum communis (EDC) muscles. Thumb extension is carried out by abductor pollicis longus (APL), extensor pollicis brevis (EPB), and extensor pollicis longus (EPL). Thus, in various clinical pathologies that may cause a dynamic imbalance between the radial-based extensors (ECRL and ECRB) versus the ulnar-based extensor (ECU), wrist extension will occur with simultaneous and involuntary radial/ulnar deviation. To achieve neutral wrist extension movements, the extensor carpi radialis brevis (ECRB), extensor carpi radialis longus (ECRL), and the extensor carpi ulnaris (ECU) muscles act synergistically based on each muscle's insertion and dynamic function. For example, lateral epicondylitis affects 1-5% of the general population. Clinical pathology affecting one or multiple muscles in this group is not uncommon. These muscles generally originate on or near the lateral epicondyle and insert on the distal forearm or in the hand. The wrist extensor muscles comprise a significant component of the posterior forearm musculature.
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