The pronator teres is a

muscle Muscle is a soft tissue, one of the four basic types of animal tissue. There are three types of muscle tissue in vertebrates: skeletal muscle, cardiac muscle, and smooth muscle. Muscle tissue gives skeletal muscles the ability to muscle contra ...

(located mainly in the

forearm The forearm is the region of the upper limb between the elbow and the wrist. The term forearm is used in anatomy to distinguish it from the arm, a word which is used to describe the entire appendage of the upper limb, but which in anatomy, techn ...

) that, along with the pronator quadratus, serves to pronate the forearm (turning it so that the palm faces posteriorly when from the

anatomical position Anatomical terminology is a specialized system of terms used by anatomists, zoologists, and health professionals, such as doctors, surgeons, and pharmacists, to describe the structures and functions of the body. This terminology incorpor ...

). It has two origins, at the medial humeral supracondylar ridge and the medial side of the coronoid process of the ulna and inserts near the middle of the

radius In classical geometry, a radius (: radii or radiuses) of a circle or sphere is any of the line segments from its Centre (geometry), center to its perimeter, and in more modern usage, it is also their length. The radius of a regular polygon is th ...

Structure

The pronator teres has two heads—humeral and ulnar. * The humeral head, the larger and more superficial, arises from the medial supracondylar ridge immediately superior to the

medial epicondyle of the humerus The medial epicondyle of the humerus is an epicondyle of the humerus bone of the upper arm in humans. It is larger and more prominent than the Lateral epicondyle of the humerus, lateral epicondyle and is directed slightly more posteriorly in the ...

, and from the common flexor tendon (which arises from the medial epicondyle). * The ulnar head (or ulnar tuberosity) is a thin fasciculus, which arises from the medial side of the coronoid process of the

ulna The ulna or ulnar bone (: ulnae or ulnas) is a long bone in the forearm stretching from the elbow to the wrist. It is on the same side of the forearm as the little finger, running parallel to the Radius (bone), radius, the forearm's other long ...

, and joins the preceding at an acute angle. The

median nerve The median nerve is a nerve in humans and other animals in the upper limb. It is one of the five main nerves originating from the brachial plexus. The median nerve originates from the lateral and medial cords of the brachial plexus, and has cont ...

enters the forearm between the two heads of the muscle, and is separated from the

ulnar artery The ulnar artery is the main blood vessel, with oxygenated blood, of the Human Anatomical Terms#Anatomical directions, medial aspects of the forearm. It arises from the brachial artery and terminates in the superficial palmar arch, which joins ...

by the ulnar head. The muscle passes obliquely across the forearm, and ends in a flat tendon, which is inserted into a rough impression at the middle of the lateral surface of the body of the

, just distal to the insertion of the

supinator In human anatomy, the supinator is a broad muscle in the posterior compartment of the forearm, curved around the upper third of the radius (bone), radius. Its function is to supination, supinate the forearm. Structure The supinator consists of tw ...

. The lateral border of the muscle forms the medial boundary of the triangular hollow known as the

cubital fossa The cubital fossa, antecubital fossa, chelidon, inside of elbow, or, humorously, wagina, is the area on the anterior side of the upper part between the arm and forearm of a human or other hominid animals. It lies anteriorly to the elbow (antecubit ...

, which is situated anterior to the

elbow The elbow is the region between the upper arm and the forearm that surrounds the elbow joint. The elbow includes prominent landmarks such as the olecranon, the cubital fossa (also called the chelidon, or the elbow pit), and the lateral and t ...

Nerve supply

The pronator teres is innervated by the

and nerve roots C6 and C7. To stimulate the pronator teres, a signal begins in the precentral gyrus in the brain and goes down through the

internal capsule The internal capsule is a paired white matter structure, as a two-way nerve tract, tract, carrying afferent nerve fiber, ascending and efferent nerve fiber, descending axon, fibers, to and from the cerebral cortex. The internal capsule is situate ...

. It continues down the corticospinal tracts through the capsule, midbrain, and pons where it arrives at the medullar pyramids. Once at the pyramids, the corticospinal tracts decussate and the signal goes down the lateral corticospinal tract until it reaches the ventral horns of C5, C6, C7, C8, and T1. The signal then goes through the ventral rami and down the root ganglions of C5, C6, C7, C8, and T1 (which together form the brachial plexus). Next, the signal goes down the median nerve branch of the

brachial plexus The brachial plexus is a network of nerves (nerve plexus) formed by the anterior rami of the lower four Spinal nerve#Cervical nerves, cervical nerves and first Spinal nerve#Thoracic nerves, thoracic nerve (cervical spinal nerve 5, C5, Cervical spi ...

and stimulates the pronator teres to contract causing the hand to pronate.

Variation

Occasionally, the ulnar head is absent. Also, additional slips from the medial intermuscular septum, from the

biceps brachii The biceps or biceps brachii (, "two-headed muscle of the arm") is a large muscle that lies on the front of the upper arm between the shoulder and the elbow. Both heads of the muscle arise on the scapula and join to form a single muscle bell ...

, and from the brachialis occasionally occur.

Function

Pronator teres pronates the forearm, turning the hand posteriorly. If the elbow is flexed to a right angle, then pronator teres will turn the hand so that the palm faces inferiorly. It is assisted in this action by pronator quadratus. It also weakly flexes the elbow, or assists in flexion at the elbow when there is strong resistance.

Clinical significance

Pronator teres syndrome is one cause of

wrist In human anatomy, the wrist is variously defined as (1) the carpus or carpal bones, the complex of eight bones forming the proximal skeletal segment of the hand; "The wrist contains eight bones, roughly aligned in two rows, known as the carpal ...

pain. It is a type of neurogenic pain. * Patients with the pronator teres syndrome have numbness in median nerve distribution with repetitive pronation/supination of the forearm, not flexion and extension of the elbow * Early fatigue of the forearm muscles is seen with repetitive stressful motion, especially pronation * EMG may show only mildly reduced conduction velocities * Despite their anatomic proximity, patients with pronator teres syndrome do not have a higher incidence of AIN syndrome * Other sites of compression: ** Ligament of Struthers ** Lacertus fibrosus ** Proximal arch of the FDS ** Rare causes such as following tendon transfers for radial palsy * Dissimilarity to CTS: ** Positive Tinel's sign in forearm rather than at wrist ** Negative Phalen's maneuver ** Dysesthesia of palmar triangle ** Pain on resistance to pronation ** Pain in forearm on resistance to isolated flexion of the PIP joint of long and ring fingers In C5 tetraplegia or radial nerve palsy patients, pronator teres tendon can be rerouted, so called

tendon transfer A tendon transfer is a surgical process in which the insertion (anatomy), insertion of a tendon is moved, but the origin (anatomy), origin remains in the same location. Tendon transfer involves redistribution of muscle power, not recreation. Tend ...

, to

extensor carpi radialis brevis In human anatomy, extensor carpi radialis brevis is a muscle in the forearm that acts to extend and abduct the wrist. It is shorter and thicker than its namesake extensor carpi radialis longus which can be found above the proximal end of the ext ...

tendon to restore wrist extension.

Etymology

The word ''pronator'' comes from the Latin ''pronus'', which means “inclined forward or lying face downward”, and has to do with the muscle's action being

pronation Motion, the process of movement, is described using specific anatomical terminology, anatomical terms. Motion includes movement of Organ (anatomy), organs, joints, Limb (anatomy), limbs, and specific sections of the body. The terminology used de ...

of the

. The Latin term ''teres'', which means "round or cylindrical shaped" or "long and round", refers to the shape of the muscle. The indirect English translation of pronator teres is therefore: cylindrical muscle that turns the forearm (and the palm along with it) down.

Additional images

Image:Gray417_color.PNG, Cross-section through the middle of the forearm. File:Muscles of forearm.jpg, Teres pronator muscle File:Muscles of upper limb.(cross section - human cadaver).jpg, Muscles of upper limb. Cross section. File:Pronator teres.svg, Simplified diagram demonstrating the attachment of the pronator teres

References

External links

* * * * {{Authority control Elbow flexors Forearm pronators Muscles of the upper limb