Radial muscles of the forearm
Anatomy and supply
The radial musculature consists of three muscles located at the lateral forearm. They all run from or near the lateral epicondyle of the humerus to the wrist. As their bellies and tendons lie superficially, they can be easily palpated. The three radial muscles are:
- Brachioradialis muscle: originates at the lateral supracondylar ridge (between the brachialis and lateral head of the triceps) and the lateral intermuscular septum of the humerus and inserts at the styloid process of the radius. This powerful muscle is mainly responsible for the lateral contour of the elbow and forearm.
- Extensor carpi radialis longus: has its origin slightly below at the lateral supracondylar ridge of the humerus and inserts distally at the posterior side of the base of the second metacarpal bone. The majority of this muscle lies underneath the brachioradialis.
- Extensor carpi radialis brevis: arises from the common extensor tendon of the superficial extensors at the lateral epicondyle of the humerus and attaches to the posterior side of the base of the third metacarpal bone.
All radial muscles are supplied by the radial nerve (C5-C8) which courses between the brachioradialis and brachialis to the elbow and there divides into a deep branch and a superficial branch at the height of the radial head. The superficial branch uses the brachioradialis as a guiding structure to reach the wrist joint and arrives at the dorsum of the hand. In contrast, the deep branch penetrates the supinator muscle and continues to the extensors of the forearm. It is important to notice that the branches supplying the brachioradialis and extensor carpi radialis longus branch off before the division of the radial nerve, whereas the nerve supplying the extensor carpi radialis brevis, the posterior interosseus nerve, arises just after the division.
The radial musculature supports movements of the elbow, hand and radioulnar joints. The brachioradialis is a strong flexor muscle of the elbow joint. Additionally it can supinate or pronate the forearm to the anatomical neutral position, but not further, which is why the flexion of the elbow is the most powerful in a neutrally positioned arm. In contrast, both the extensor carpi radialis longus and brevis are rather poor flexors of the elbow. Their main function is the dorsal extension and radial abduction of the wrist joint. They also contribute to a strong fist closure by previously stretching the flexor muscles of the hand and fingers.
In neurological examinations, the brachioradialis serves as a reference muscle for the nerve roots C5 and C6, by means of the brachioradialis reflex. It is performed by striking on the tendon at the distal end of the radius causing a flexion of the elbow joint. A weakened or absent reflexive contraction can be of diagnostic relevance for a lesion at the nerve roots. An alternative or addition to the brachioradialis reflex is the biceps reflex.
In many sports and occupational activities, a permanent extension of the wrist joint is demanded (e.g. driving of screws or painting the wall). In the long term continuous false strain can lead to microtraumata, inflammation or tears in the tendon of the extensor muscles of the wrist joint. The tendon of the extensor carpi radialis brevis is particularly prone to these lesions (lateral epicondylitis) causing pain at the lateral part of the elbow and a reduced ability to extend one’s hand. As tennis players are especially affected by this condition, it is also referred to as the tennis elbow.