Pronator teres

Origin

The pronator teres is a superficial muscle located in the anterior (flexor-pronator) compartment of the forearm. It typically originates with two heads:

• Humeral head: This is the larger, more superficial head, arising from the medial epicondyle of the humerus via the common flexor tendon

• Ulnar head: This smaller head originates from the coronoid process of the ulna and joins the humeral head at an acute angle.

Insertion

The muscle courses obliquely across the forearm, terminating in a flat tendon. This tendon inserts onto a rough impression on the lateral surface of the midshaft of the radius.

Innervation

The pronator teres is innervated by the median nerve. This nerve is clinically significant as it passes directly between the two heads of the muscle, making this a common site for median nerve compression (known as pronator syndrome). The ulnar head of the pronator teres also separates the median nerve from the ulnar artery underneath, as the nerve enters the forearm.

Action

The primary function of the pronator teres is the pronation of the forearm, working in conjunction with the pronator quadratus. It also serves as a weak flexor of the elbow joint.

Relationships

The lateral border of the pronator teres forms the medial boundary of the cubital fossa, a triangular depression anterior to the elbow joint. Distally, the muscle is covered by the brachioradialis before its insertion on the radius. It lies immediately distal to the attachment of the supinator muscle on the radius.