The pronator teres is a muscle (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 most often used to describe the entire appendage of the upper limb, but which in an ...

) that, along with the

pronator quadratus Pronator quadratus is a square-shaped muscle on the distal forearm that acts to pronate (turn so the palm faces downwards) the hand. Structure Its fibres run perpendicular to the direction of the arm, running from the most distal quarter of the a ...

, serves to

pronate Motion, the process of movement, is described using specific anatomical terms. Motion includes movement of organs, joints, limbs, and specific sections of the body. The terminology used describes this motion according to its direction relativ ...

the forearm (turning it so that the palm faces posteriorly when from the anatomical position). It has two attachments, to the medial humeral supracondylar ridge and the ulnar tuberosity, and inserts near the middle of the radius.

Structure

The pronator teres has two heads—humeral and ulnar. * The humeral head, the larger and more superficial, arises from the

medial supracondylar ridge The inferior third of the medial border of the humerus is raised into a slight ridge, the medial supracondylar ridge (or medial supracondylar line), which becomes very prominent below; it presents an anterior lip for the origins of the Brachiali ...

immediately superior to the medial epicondyle of the humerus, and from the

common flexor tendon The common flexor tendon is a tendon that attaches to the medial epicondyle of the humerus (lower part of the bone of the upper arm that is near the elbow joint). It serves as the upper attachment point for the superficial muscles of the fron ...

(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 (''pl''. ulnae or ulnas) is a long bone found in the forearm that stretches from the elbow to the smallest finger, and when in anatomical position, is found on the medial side of the forearm. That is, the ulna is on the same side of t ...

, 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 medial aspects of the forearm. It arises from the brachial artery and terminates in the superficial palmar arch, which joins with the superficial branch of the radial ar ...

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 radius, just distal to the insertion of the supinator. The lateral border of the muscle forms the medial boundary of the triangular hollow known as the

cubital fossa The cubital fossa, chelidon, or elbow pit, is the triangular area on the anterior side of the upper limb between the arm and forearm of a human or other hominid animals. It lies anteriorly to the elbow (Latin ) when in standard anatomical position ...

, which is situated anterior to the

elbow The elbow is the region between the 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 the m ...

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 The precentral gyrus is a prominent gyrus on the surface of the posterior frontal lobe of the brain. It is the site of the primary motor cortex that in humans is cytoarchitecturally defined as Brodmann area 4. Structure The precentral gyrus li ...

in the brain and goes down through the internal capsule. 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 The pyramidal tracts include both the corticobulbar tract and the corticospinal tract. These are aggregations of efferent nerve fibers from the upper motor neurons that travel from the cerebral cortex and terminate either in the brainstem (''cort ...

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 formed by the anterior rami of the lower four cervical nerves and first thoracic nerve ( C5, C6, C7, C8, and T1). This plexus extends from the spinal cord, through the cervicoaxillary canal in th ...

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 ( la, musculus 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 t ...

, and from the

brachialis The brachialis (brachialis anticus), also known as the Teichmann muscle, is a muscle in the upper arm that flexes the elbow. It lies deeper than the biceps brachii, and makes up part of the floor of the region known as the cubital fossa (elbow p ...

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

. It also weakly flexes the elbow, or assists in flexion at the elbow when there is strong resistance.

Clinical significance

Pronator teres syndrome Pronator teres syndrome is a compression neuropathy of the median nerve at the elbow. It is rare compared to compression at the wrist (carpal tunnel syndrome) or isolated injury of the anterior interosseous branch of the median nerve ( anterior int ...

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 fibrosis ** Proximal arch of the FDS ** Rare causes such as following tendon transfers for radial palsy * Dissimilarity to CTS: ** Positive

Tinel's sign Tinel's sign (also Hoffmann-Tinel sign) is a way to detect irritated nerves. It is performed by lightly tapping ( percussing) over the nerve to elicit a sensation of tingling or "pins and needles" in the distribution of the nerve. Percussion is usu ...

in forearm rather than at wrist ** Negative

Phalen's maneuver Phalen's maneuver is a diagnostic test for carpal tunnel syndrome by an American orthopedist named George S. Phalen. Technique The patient is asked to hold their wrists in complete and forced flexion (pushing the dorsal surfaces of both han ...

** 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, 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 exte ...

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 terms. Motion includes movement of organs, joints, limbs, and specific sections of the body. The terminology used describes this motion according to its direction relativ ...

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