Pronator teres muscle
Pronator teres is a fusiform muscle found in the anterior forearm. It belongs to the group of superficial flexors of the forearm, together with flexor carpi radialis, palmaris longus, flexor digitorum superficialis and flexor carpi ulnaris muscles. Pronator teres is the most lateral muscle of this group. It is composed of two heads named after the bones from which they originate;
- Humeral head that arises from the distal aspect of humerus
- Ulnar head that arises from coronoid process of ulna
|Origin||Humeral head: medial supracondylar ridge of humerus
Ulnar head: Coronoid process of ulna
|Insertion||Lateral surface of radius (distal to supinator)|
|Action||Pronation of forearm at the proximal radioulnar joint, flexion of the forearm at the elbow joint|
|Innervation||Median nerve (C6, C7)|
|Blood supply||Branches of brachial, radial and ulnar arteries|
In this article, we will discuss the anatomy and function of pronator teres muscle.
- Origin and insertion
- Blood supply
- Clinical relations
Origin and insertion
Pronator teres muscle arises by two heads named after their origin sites. The humeral head (superficial head) originates from the medial supracondylar ridge of humerus, located superior to the medial epicondyle of humerus and inferior to the attachment of brachialis muscle. The ulnar head (deep head) originates from the coronoid process of ulna. This area is located between the attachments of brachialis and flexor digitorum superficialis muscles, and superior to the origin of flexor pollicis longus muscle.
From their origin areas, the two muscle heads run inferolaterally, coursing under the brachioradialis muscle. The two heads eventually fuse into a single muscle belly that inserts via flat tendon onto the lateral surface of the radius, specifically at the rough area at the middle of its shaft called the pronator tuberosity. This area is located inferior to the insertion of supinator muscle.
Being directly lateral to flexor carpi radialis muscle, pronator teres is the most lateral of the superficial flexors of the forearm. In its proximal part, the muscle lies deep to flexor digitorum superficialis, while the distal anterior surface is covered by brachioradialis muscle.
Pronator teres muscle forms the medial margin of the cubital fossa (elbow pit). This fossa contains several neurovascular structures that are related to pronator teres. Brachial artery gives off ulnar and radial arteries near the upper margin of pronator teres. After branching off, ulnar artery passes posterior to the muscle while radial artery follows its upper edge. Median nerve runs in between two heads of pronator teres; the ulnar head of the muscle separates the nerve from the ulnar artery.
Pronator teres muscle receives its innervation from median nerve (root value C6 and C7), which is a branch of brachial plexus (C5-T1).
The vascularization for pronator teres muscle comes from three arteries;
- Branches of ulnar artery; common interosseus artery, anterior ulnar recurrent artery
- Branch of radial artery; radial recurrent artery
- Branches of brachial artery; inferior ulnar collateral arteries
As its name suggests, the main action of pronator teres is the pronation of the forearm, which is an exclusive upper limb movement. The muscle pulls the radius medially, causing its head to rotate around the proximal part of ulna at the proximal radioulnar joint.
This action rotates the palm of the hand as well, bringing it into a position to face the ground, i.e. pronation. Since it crosses the elbow joint, pronator teres also assists in the flexion of the forearm.
Pronator teres syndrome
Pronator teres syndrome is a neuropathy caused by the compression of median nerve at the proximal aspect of the forearm. Median nerve is usually compressed between two heads of pronator teres muscle. This condition can be caused by acute compressions of the nerve due to inflammation of the muscle (myositis) or injury to the elbow region. The long-term compression is also possible and it's commonly referred to as the “honeymoon paralysis” since it usually occurs due to the sleeping on the partner's arm.
The main clinical signs include numbness and/or pain in the innervation region of median nerve and malfunction of flexor pollicis longus and flexor digitorum profundus of the index finger and the pronator quadratus. The diagnosis is established by a neurological exam and imaging techniques (for example MRI scan).