Muscles flexing the elbow joint

Biceps brachii

Brachialis

Brachioradialis

Pronator teres

Brachialis

Brachialis lies under cover of biceps brachii in the lower half of the anterior aspect of the arm. It arises from the distal two-thirds of the anterior surface of the shaft of the humerus extending outwards onto the medial and lateral intermuscular septa. The muscle fibers are separated from the lower part of the lateral intermuscular septum by brachioradialis, with which it may be partly fused, and extensor carpi radialis longus. The fibres converge to a thick tendon which forms the floor of the cubital fossa and attaches to the rough triangular brachialis impression on the inferior part of the coronoid process and tuberosity of the ulna. Some deeper fibres of brachialis insert into the capsule of the elbow joint and serve to pull it away from the moving bones during flexion and prevent them from becoming trapped.

Nerve supply

Brachialis is supplied mainly by the musculocutaneous nerve, root value C5 and 6; but also receives a branch from the radial nerve; again root value C5 and 6, as it runs along the lateral border of the muscle. However, this latter branch is thought to be almost entirely sensory.

Action

Brachialis is the main flexor of the elbow joint.

Functional activity

Although brachialis flexes the elbow, it is important in controlling extension produced by gravity. In this situation, the flexors of the elbow control the movement by an eccentric contraction.

Palpation

When biceps brachii has been identified, brachialis can be felt extending either side of its belly with the elbow flexed. The tendon can be palpated by applying deep pressure just above the coronoid process of the ulna.

Brachioradialis

Brachioradialis is a superficial muscle found on the lateral side of the forearm extending almost as far as the wrist. It forms the lateral border of the cubital fossa, and is covered in its upper part by brachialis, with which it may be partly fused. The proximal attachment of brachioradialis is to the upper two-thirds of the front of the lateral supracondylar ridge of the humerus and the adjacent part of the lateral intermuscular septum. From here, the fibres run downwards forming a long, narrow, flat tendon in the middle of the forearm. The tendon is crossed by those of abductor pollicis longus and extensor pollicis brevis before it attaches to the lateral surface of the radius just above the styloid process.

Nerve supply

Brachioradialis is supplied by a branch from the radial nerve, root value C5 and 6, which enters its medial side above the elbow. The skin over the muscle is also supplied by roots C5 and 6.

Action

Brachioradialis flexes the elbow joint particularly when the forearm is midway between pronation and supination. It also helps to return the forearm to this mid position from the extremes of either pronation or supination; this can be confirmed by palpation.

Functional activity

Brachioradialis acts primarily to maintain the integrity of the elbow joint since its fibres run more or less parallel to the radius. It also works eccentrically as an extensor of the elbow joint in activities such as hammering.

Palpation

With the elbow flexed to 90° and forearm in a mid-pronated position, the brachioradialis can be felt along the top of the forearm when the position is maintained against resistance. Using firm pressure, the tendon can be palpated proximal to the radial styloid process. The brachioradialis reflex can be elicited by firmly tapping its tendon just above the wrist.

Pronator teres

Pronator teres forms the medial border of the cubital fossa at the elbow, and as such is the most lateral of the superficial muscles in the flexor compartment of the forearm. It arises by two heads: the humeral head and the ulnar head. The humeral head arises from the lower part of the medial supracondylar ridge and adjacent intermuscular septum. It also comes from the common flexor origin on the medial epicondyle and the covering fascia. The ulnar head arises from the pronator ridge, which runs downwards from the medial part of the coronoid process, to join with the humeral head on its deep surface. Between these two heads passes the median nerve. The muscle fibres pass downwards and laterally to attach via a flattened tendon into a roughened oval area on the middle of the lateral surface of the radius.

Nerve supply

Pronator teres is supplied by the median nerve, root values C6, 7. The overlying skin is supplied by roots C6 and T1.

Action

Pronator teres pronates the forearm by producing an anteromedial swing  of the lower end of the radius across the ulna. This movement of the radius carries the hand with it. Pronator teres is also a weak flexor of the elbow.

Palpation

The muscle can be palpated running along the medial border of the cubital fossa between the medial epicondyle of the humerus and the middle of the radius. Pronator teres can be most easily felt, and occasionally seen, when resisting pronation of the forearm.