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The pronator teres is a muscle that pronates the forearm and assists in flexion of the elbow joint. It acts in conjunction with the pronator quadratus. The pronator teres is a long, round muscle located on the anterior aspect of the forearm. It originates from the medial epicondyle and attaches to the flexor retinaculum of the wrist. It also attaches to the base of metacarpals II and III, allowing for flexion and abduction at the wrist. The median nerve passes between the two heads of the pronator teres, making it susceptible to nerve entrapment. This article will explore the role of the pronator teres muscle in decelerating pronation and provide insights into its anatomy, function, and clinical implications.
| Characteristics | Values |
|---|---|
| Muscle | Pronator Teres |
| Location | Anterior aspect of the forearm |
| Shape | Long and round |
| Points of origin | Humeral head, ulnar head |
| Attachments | Flexor retinaculum of the wrist, base of metacarpals II and III |
| Actions | Pronation of the forearm, flexion of the wrist, flexion of the elbow joint |
| Innervation | Median nerve |
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What You'll Learn
Forearm pronation and supination
The triangular fibrocartilage connects the bones and ensures they remain together during pronation and supination. It is thicker at its periphery than at its centre. The thick apex of the triangle attaches to the ulnar styloid process, and its thin base attaches to the prominent edge of the radius, just proximal to the radiocarpal articulation. The triangular fibrocartilage also separates the wrist joint (radiocarpal joint) from the lunate and triquetrum bones. The ulnar notch of the radius pivots around the head of the ulna during pronation and supination.
A thin ligamentous cord, known as the interosseous membrane, keeps the radius and ulna bonded during supination and pronation. It also transfers forces between the two bones, and numerous muscles such as flexor digitorum profundus arise from it. This membrane arises from the ulnar tuberosity distal to the annular ligament and inserts onto the posteromedial aspect of the radial shaft in an oblique fashion. Its fibres run from medial to lateral to stabilise the proximal radioulnar joint, but some individuals lack this membrane.
The median nerve innervates the flexor digitorum superficialis muscle of the anterior compartment of the forearm. It has two heads, an ulnar and a humeral head. The larger and more superficial humeral head arises from the medial supracondylar ridge. The median nerve passes through the two heads to reach the forearm, and it is separated from the ulnar artery by the ulnar head. The muscle inserts onto the lateral surface of the radius distal to the supinator, causing pronation when it contracts.
The anterior interosseus nerve, a branch of the median nerve, innervates the flexor digitorum profundus muscle in the anterior compartment of the forearm. It arises from the distal anterior surface of the ulna and inserts onto the distal anterior shaft of the radius to cause pronation when it contracts.
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Pronator teres muscle
The pronator teres is a muscle located mainly in the forearm. It is a long, round muscle that is part of the group of superficial flexors of the forearm. The muscle has two heads, the humeral head and the ulnar head, which originate from different parts of the body. The humeral head, the larger and more superficial of the two, arises from the medial supracondylar ridge of the humerus, which is located superior to the medial epicondyle of the humerus. The ulnar head, on the other hand, arises from the coronoid process of the ulna and is deeper, joining the humeral head at an acute angle.
The pronator teres is the most lateral muscle of the superficial flexors group. It forms the medial border of the cubital fossa, an anatomical triangle located over the elbow. The median nerve, which innervates the pronator teres, runs between the two heads of the muscle. The ulnar head of the muscle separates the nerve from the ulnar artery. The vascularization for the pronator teres comes from three arteries: branches of the ulnar artery, the common interosseus artery, and the anterior ulnar recurrent artery.
The main action of the pronator teres is the pronation of the forearm, which involves turning the forearm so that the palm faces downwards. It pulls the radius medially, causing the head to rotate around the proximal part of the ulna at the proximal radioulnar joint. This action also rotates the palm of the hand, bringing it into a position facing the ground. In addition to pronation, the pronator teres also assists in the flexion of the forearm at the elbow joint.
The pronator teres works synergistically with the pronator quadratus muscle. When the elbow is fully flexed, the muscle fibres of the pronator teres are shortened, making them less able to produce force. This muscle is absent in about 15% of the population.
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Pronator quadratus muscle
The pronator quadratus muscle is a square-shaped muscle on the distal forearm. It is deep-seated, short, flat, and quadrilateral, with fibres running in a parallel direction. The muscle is compacted in a small closed compartment, covered by the interosseous membrane dorsally and by its own fascia volarly. It is the only muscle that attaches only to the ulna at one end and the radius at the other.
The pronator quadratus originates from the anterior surface of the ulna and attaches to the anterior surface of the radius. Its fibres run perpendicular to the direction of the arm, running from the most distal quarter of the anterior ulna to the distal quarter of the radius.
The muscle's action is to pronate the forearm, or turn the hand so that the palm faces downwards. When the pronator quadratus contracts, it pulls the lateral side of the radius towards the ulna, resulting in the pronation of the radioulnar joint.
The pronator quadratus is innervated by the anterior interosseous nerve, a branch of the median nerve. It is vascularised by the anterior interosseous artery.
The pronator quadratus can be absent in some humans, although this does not significantly affect the action of pronation as the pronator teres plays the major role in this movement.
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Median nerve
The median nerve is a major peripheral nerve in the upper limb of humans and other animals. It is one of the five main nerves originating from the brachial plexus, a complex network of nerves that helps control movement in the shoulders, arms, and hands. The median nerve is the only nerve that passes through the carpal tunnel, a space in the wrist that holds the nerve and tendons.
The nerve starts at the armpit and connects to nerve roots in the brachial plexus that run from the C5 to C8 cervical vertebrae and the T1 thoracic vertebra. It then passes vertically down the arm, initially situated lateral to the brachial artery. Halfway down the arm, the nerve crosses over the brachial artery and becomes medial to it. It enters the anterior compartment of the forearm via the cubital fossa, a triangular space opposite the elbow joint.
In the forearm, the median nerve travels between the two heads of the pronator teres muscle, then descends between the flexor digitorum profundus and flexor digitorum superficialis muscles. The nerve gives rise to two major branches in the forearm: the anterior interosseous nerve and the palmar cutaneous nerve. The anterior interosseous nerve supplies the deep muscles in the anterior forearm, while the palmar cutaneous nerve innervates the skin of the lateral palm.
After giving off these branches, the median nerve enters the hand through the carpal tunnel, where it terminates by dividing into two branches: the recurrent branch and the palmar digital nerves. The recurrent branch innervates the thenar muscles, while the palmar digital nerves innervate the palmar surface and fingertips of the lateral three and a half digits.
The median nerve provides both sensory and motor functions to the forearm, wrist, and hand. It helps control movement and sensation in these areas, allowing for bending and straightening of the wrists, thumbs, and fingers, as well as pronation of the forearm. It also sends touch, pain, and temperature sensations from the lower arm and hand to the brain. A pinched median nerve can cause carpal tunnel syndrome, resulting in wrist pain and problems grasping and holding items.
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Manual muscle testing
Forearm Pronation
During forearm pronation manual muscle testing, it is common for the biceps brachii muscle to assist in the movement. To isolate the pronator teres muscle, the examiner can ask the patient to flex their elbow slightly while performing the test. The examiner should also ensure that the patient is not compensating by using their shoulder or trunk muscles. The examiner should apply resistance gradually and avoid sudden movements to prevent injury and ensure accurate results.
For Grade 1, palpate the pronator teres muscle in the upper third of the volar surface of the forearm, along a diagonal line from the medial condyle of the humerus to the lateral border of the radius. Contractile activity should be present, but no hand movement is expected. If there is no contractile activity, the grade is 0.
Forearm Supination
For Grade 1, palpate the supinator muscle distal to the head of the radius on the dorsal aspect of the forearm. There should be no limb movement, but contractile activity should be present. If there is no contractile activity, the grade is 0.
For grades 3 to 5, the patient should be in a short sitting position, with their arm at their side and their elbow flexed to 90 degrees. The therapist should stand at the side or in front of the patient, supporting the patient's elbow with one hand and using the other hand to provide resistance by grasping the forearm on the volar aspect of the wrist. The patient begins in pronation and moves to supination until their palm faces the ceiling. The therapist applies resistance in the direction of pronation.
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Frequently asked questions
Pronation is the movement of the hands to turn the palms posteriorly or inferiorly, depending on the position of the arm. In other words, it involves placing the palms into the prone (face-down) position.
The pronator teres and pronator quadratus are two muscles in the forearm that work together to achieve pronation by pulling on the radius bone of the forearm.
The pronator teres muscle pronates the forearm and assists in flexion of the elbow joint. It acts synergistically with the pronator quadratus.
The pronator teres muscle has two points of origin: the humeral head and the ulnar head. The humeral head is larger and more superficial, while the ulnar head is deeper and joins it at an acute angle.
To target the pronator teres muscle specifically, the elbow should not be excessively flexed. If the elbow is fully flexed, the muscle fibres will be shortened and less able to produce force.
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