The pronator teres is a muscle located in the forearm. The muscle has two heads; the superficial head, which is the humeral head, arises from the medial epicondyle of the humerus and a deep head, which is the ulnar head, arises from the medial border of the coronoid process of the ulna. The pronator teres muscle is inserted into the middle of the lateral surface of the shaft of the radius.
Function
The function of the pronator teres is pronation and supination of the forearm. It also assists in flexion of the forearm at the elbow.
When fractures occur below the insertion of the pronator teres muscle, the proximal fragment is usually pulled into pronation. The forearm will still have a normal rotation range of 160-180 degrees. Sometimes, a decrease in rotation motion by 50 degrees may not be noticed, however, every attempt should be made to reduce the forearm fracture well, especially fractures of the proximal radius, which are prone to malrotation. The bicipital tuberosity of the radius is used as a guide to the rotation of the proximal radius. The position of the thumb should be compared to the position of the radial tuberosity.
Innervation
The pronator teres muscle in innervated by the median nerve. The condition of high radial nerve palsy is helped by transfer of the pronator teres muscle. Extension of the wrist, which is impaired by high radial nerve palsy, is improved by transfer of the pronator teres to the extensor carpi radialis brevis muscle.
Main Relationship to the Pronator Teres
The median nerve passes between the two heads of the pronator teres. The ulnar head (deep head) separates the median nerve from the ulnar artery. The median neve runs above the deep head while the ulnar artery runs below the deep head.
It seems as if when a nerve enters the forearm, it goes between two heads of a muscle. Some examples include the posterior interosseous nerve, the ulnar nerve, and the median nerve. The posterior interosseous nerve enters the extensor compartment of the forearm between the two heads of the supinator muscle. It can be compressed at the Arcade of Frohse. The ulnar nerve enters the forearm by passing through the two heads of the flexor carpi ulnaris muscle. Finally, the median nerve enters the forearm by passing through the two heads of the pronator teres muscle. A condition called pronator teres syndrome can occur due to entrapment of the median nerve between the two heads of the pronator teres muscle. Other elements may cause pronator teres syndrome, however, entrapment of the median nerve is the main cause.
