Dominic Stone
The human body is a complex machine, with muscles that contract and relax to enable movement. The muscles that rotate the forearm are the supinator and the pronator teres. These muscles facilitate the movements of supination and pronation, which are essential for everyday activities like eating and drinking. The supinator muscle rotates the forearm to turn the palm upward, while the pronator teres helps in pronating the forearm, turning the palm downward. Understanding the movement of the elbow and forearm is crucial when addressing hand and wrist issues, and common sports like tennis and golf are associated with overuse injuries at the elbow joint.
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What You'll Learn
Supinator and pronator teres muscles
The primary muscles that rotate the forearm are the supinator and the pronator teres. These muscles facilitate the movements of supination and pronation. The supinator muscle is responsible for rotating the forearm and turning the palm upward (supination). The supinator receives its nerve supply from the deep branch of the radial nerve, which arises from the posterior cord and the nerve roots C5-T1.
The pronator teres, on the other hand, assists in pronating the forearm, turning the palm downward (pronation). The muscle passes obliquely across the forearm and ends in a flat tendon, which is inserted into the middle of the lateral surface of the body of the radius. The pronator teres has two heads: the humeral head and the ulnar head. The humeral head is larger and more superficial, arising from the medial supracondylar ridge of the humerus. The ulnar head, also known as the ulnar tuberosity, is a thin fasciculus that arises from the medial side of the coronoid process of the ulna and joins the preceding head at an acute angle.
The median nerve enters the forearm between these two heads, and it is separated from the ulnar artery by the ulnar head. The nerve supply to the pronator teres originates in the precentral gyrus of the brain and travels through the internal capsule, midbrain, and pons before reaching the medullar pyramids. At the pyramids, the nerve signals cross over to the lateral corticospinal tract and continue down to the ventral horns of C5, C6, C7, C8, and T1. From there, the signal moves through the ventral rami and the root ganglions of the same spinal nerves, forming the brachial plexus. Finally, the signal travels through the median nerve branch of the brachial plexus to stimulate the pronator teres contraction, resulting in forearm pronation.
It is important to note that the supinator and pronator teres muscles work synergistically during forearm rotation. While the supinator is responsible for supination, the pronator teres assists in pronation, allowing for a full range of motion in the forearm. These muscles are essential for various functional movements, such as turning a screwdriver or a key, which require both supination and pronation.
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Supination and pronation movements
The forearm is the part of the upper limb below the elbow joint. It has two bones: the radius and the ulna. The forearm can rotate at the elbow and wrist joints, allowing for unique movements of supination and pronation. These movements are essential for various daily activities and provide enhanced functionality to the upper limb.
Supination
Supination is the movement of the forearm that turns the palm upward. The supinator muscle of the forearm and the biceps brachii of the upper arm are responsible for this movement. They work together to pull on the radius bone, rotating it in the opposite direction of the pronator muscles. This motion turns the palm anteriorly or superiorly to the supine (face-up) position. An example of supination is the movement of the hand when looking at the palm or holding a bowl of soup.
Pronation
Pronation is the movement of the forearm that turns the palm downward. The pronator teres and pronator quadratus muscles in the forearm work together to achieve pronation by pulling on the radius bone. The radius rotates at the elbow and wrist joints around the ulna, allowing the hand, wrist, and forearm to turn almost 180 degrees. This movement places the palm into the prone (face-down) position, as seen when looking at the back of the hand.
Muscles Involved in Supination and Pronation
The primary muscles involved in supination and pronation are the supinator and the pronator teres, respectively. While the supinator muscle is responsible for rotating the forearm to turn the palm upward, the pronator teres helps in pronating the forearm, turning the palm downward. Other muscles, such as the biceps brachii, assist in supination, while the brachioradialis semi-pronates the forearm when the elbow is flexed.
Clinical Relevance
Injuries or fractures involving the radius and ulna bones can result in the loss of supination and pronation movements. For example, a Monteggia fracture, which involves the upper end of the ulna and the dislocation of the upper end of the radius, can cause a loss of these movements. Similarly, a Galeazzi fracture, which affects the lower end of the radius and the distal radioulnar joint, can also lead to the loss of pronation and supination.
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Brachialis and coracobrachialis muscles
While the brachialis and coracobrachialis muscles are important for arm and shoulder movement, they do not directly contribute to the rotation of the forearm. Instead, the primary muscles that enable forearm rotation are the supinator and pronator teres.
Brachialis Muscle
The brachialis is a muscle that flexes the elbow. It is one of the muscles that cause supination while the elbow is in flexion.
Coracobrachialis Muscle
The coracobrachialis is a slender muscle that originates from the deep surface of the coracoid process of the scapula. It is located in the upper medial part of the arm, within the anterior compartment of the arm. The coracobrachialis flexes and adducts the arm at the shoulder joint, bringing the arm forward, as happens during normal walking. It also pulls the arm in towards the body (adduction), working with the deltoid to stabilize the arm while reaching. The main blood supply to the coracobrachialis comes from the muscular branches of the brachial artery, with additional supply from the anterior circumflex humeral and thoracoacromial arteries.
Overuse of the coracobrachialis can lead to stiffening or hardening of the muscle, with symptoms including pain in the arm and shoulder, radiating down to the back of the hand. In severe cases, the musculocutaneous nerve can become trapped, causing disturbances in sensation to the skin on the radial part of the forearm and weakened flexion of the elbow. However, rupture of the coracobrachialis is extremely rare and usually only occurs due to direct trauma or avulsion from the coracoid as a result of indirect forces.
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Elbow flexion and supination
The supinator and the pronator teres are the primary muscles that rotate the forearm. These muscles facilitate the movements of supination and pronation. The supinator muscle is responsible for rotating the forearm to turn the palm upward (supination), while the pronator teres helps in pronating the forearm, turning the palm downward.
The biceps brachii muscle also plays a role in forearm supination, contributing to the strength of the movement. At 90 degrees of elbow flexion and the upper arm in full pronation, the supination strength is at its greatest. This is the position where the biceps brachii muscle has the most significant impact on supination strength.
The biceps brachii muscle has multiple functions, including stabilization, assistance in arm abduction, flexion, and internal rotation. In the elbow joint, it acts as a flexor and a supinator. Lesions of the long head of the biceps tendon (LHBT) are a common cause of pain and functional impairment of the shoulder.
In addition to the muscles mentioned, other muscles in the arm and forearm contribute to various movements. The coracobrachialis, for example, is responsible for flexing the shoulder and bringing the arm forward during normal walking. It also works with the deltoid muscle to stabilize the arm while reaching. The flexor digitorum profundus, located deep in the forearm, allows us to bend the index, middle, ring, and small fingers.
Other muscles in the arm and forearm include the brachioradialis, the flexor carpi ulnaris, and the flexor pollicis longus. These muscles have various functions, such as bending and deviating the wrist, allowing us to bend the tip of our thumb, and assisting in elbow flexion.
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Forearm pronation and supination
The primary muscles that rotate the forearm and facilitate the movements of supination and pronation are the supinator and the pronator teres. The supinator muscle is responsible for rotating the forearm to turn the palm upward (supination), while the pronator teres helps in pronating the forearm, turning the palm downward (pronation).
Supination and pronation are terms used to describe the up or down orientation of your hand, arm, or foot. When the palm or forearm faces up, it is supinated, and when it faces down, it is pronated. These movements are essential for grip, hand movement, and the everyday functioning of the upper limb. For example, turning a screwdriver or a key involves pronation and supination.
The forearm is composed of two long bones: the ulna and radius. The ulna remains stable, while the radius rotates to supinate or pronate the hand. During pronation and supination, the triangular fibrocartilage connects the bones and ensures they remain together. It is thicker at its periphery than at its centre, with its thick apex attaching to the ulnar styloid process and its thin base attaching to the prominent edge of the radius. The ulnar notch of the radius pivots around the head of the ulna during these movements.
A thin ligamentous cord, known as the membrane, keeps the radius and ulna bonded during supination and pronation. It also transfers forces between the two bones, and numerous muscles, such as the flexor digitorum profundus, arise from it. The median nerve innervates the muscle of the anterior compartment of the forearm, passing through the two heads of the muscle to reach the forearm. When the muscle contracts, it inserts onto the lateral surface of the radius distal to the supinator, causing pronation.
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Frequently asked questions
The supinator and the pronator teres muscles are the primary muscles that rotate the forearm.
The supinator muscle is responsible for rotating the forearm to turn the palm upward, which is called supination.
The pronator teres muscle helps in pronating the forearm, turning the palm downward.
No, these muscles do not directly contribute to the rotation of the forearm. Instead, the brachialis flexes the forearm and assists in supination.
Eating, turning a doorknob, playing golf and tennis are some common activities that involve forearm rotation.
