Anatomical Location and Attachments
- Origin: Lateral supracondylar ridge of the humerus.
- Insertion: Dorsal surface of the base of the 2nd metacarpal bone.
Topographically, this muscle lies most laterally in the forearm. On a cross-section of the middle third of the forearm, it is located laterally along with the brachioradialis (m. brachioradialis) and extensor carpi radialis brevis (m. extensor carpi radialis brevis). For spatial orientation: anteriorly at this level are the flexor digitorum superficialis, pronator teres, flexor carpi radialis, and palmaris longus; posteriorly are the extensor digitorum and extensor carpi ulnaris; and between the bones are the flexor digitorum profundus, flexor pollicis longus, and supinator.
Function
The primary function of the extensor carpi radialis longus is wrist extension. Additionally, the muscle abducts the wrist, producing radial deviation.
Blood Supply and Innervation
- Blood Supply: Branches of the radial artery (a. radialis) and radial recurrent artery (a. recurrens radialis).
- Innervation: Radial nerve (n. radialis, C6–C7 segments).
Topography and Neighboring Structures
At the elbow joint level, cross-sectional structures include the extensor carpi radialis longus, brachioradialis, and aconeus muscles, biceps and triceps brachii tendons, and the lateral epicondyle. Important neurovascular bundles, including the radial, median, and ulnar nerves, pass through this region.
In standard anatomical descriptions, the muscle participates in forming the radial nerve tunnel (canal). This space is formed by three muscles overlying the nerve: the brachioradialis, extensor carpi radialis longus, and extensor carpi radialis brevis. Medial to the nerve in this zone lies the brachialis (m. brachialis), while posteriorly lies the lateral epicondyle of the humerus.
Clinical Significance
- Wartenberg Syndrome (Cheiralgia Paresthetica): Entrapment of the superficial branch of the radial nerve can occur due to compression between the tendons of the brachioradialis and extensor carpi radialis longus. This is provoked by forearm pronation and ulnar flexion (e.g., prolonged computer mouse use), external compression (watch straps, handcuffs), or iatrogenic causes (chronic compression following creation of an arteriovenous fistula between the radial artery and cephalic vein for hemodialysis).
- Electromyography (EMG): The extensor carpi radialis longus is a target muscle for needle EMG examinations. The study is performed to assess the severity of denervation and reinnervation changes. The examiner evaluates spontaneous activity, motor unit action potential (MUAP) recruitment, and MUAP parameters.