Pronation and supination

Mnemonic

Pronation and supination can easily be confused, so learn the following mnemonic to help you differentiate them!

Supinate to the Sun and Pronate to the Plants

• Supinate: palm towards the Sun
• Pronate: palm towards the Plants
  

Pronation and supination are only two of the numerous body movements - how well do you know the others? Test your knowledge with our basic medical terminology quizzes and labeled diagrams. 

Proximal radioulnar joint

This is a pivot joint located between the head of the radius and the radial notch of the ulna. It is enclosed within the same articular capsule as the elbow (humeroulnar joint). The head and neck of the radius sit in the tough fibers of the circular anular ligament, which surrounds them like a collar around a neck. The ligament arises from and inserts back onto the radial notch. The superior fibers of the ligament blend with the ligaments of the elbow, and the lower fibers contribute to the quadrate ligament. The inner ligament is lined with a synovial membrane that ensures smooth action during pronation and supination. Superficially, the radial collateral ligament of the elbow supports the anular ligament. The quadrate ligament sits distally to the anular ligament to prevent excessive supination and strengthen the link between the head of the radius and the ulna. Movements at this joint are restricted to supination and pronation. Flexion and extension of the elbow occur at the humeroulnar joint.

Distal radioulnar joint 

This pivot joint is located distally near the wrist joint, and is formed between the head of the ulna, and the ulnar notch of the radius. The anterior and posterior radioulnar ligaments, as well as a triangular fibrocartilaginous plate support this joint. This 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.

Interosseus membrane

This is a tough membrane of connective tissue that connects the interosseus border of the ulna with the interosseus border of the radius. Its fibers run laterally in an oblique fashion along the entire shaft of both bones and are perforated distally to allow vessels to pass between the anterior and posterior compartments of the forearm (aperture for the anterior interosseous artery). 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 flexor digitorum profundus arise from it.

Learn more about the anatomy of the radius and ulna with our fun quizzes and diagram exercises. 

Oblique cord 

This is a flat, thin ligamentous cord that arises from the ulnar tuberosity distal to the anular ligament, and inserts onto the posteromedial aspect of the radial shaft (just inferior to the radial tuberosity) in an oblique fashion. Hence, its fibers run from medial to lateral to stabilize the proximal radioulnar joint, but are absent in some individuals.

Refresh your knowledge on the different joint types with this fun quiz!

Pronator teres

The median nerve innervates this muscle of the anterior compartment of the forearm. It has two heads, an ulnar and a humeral. The larger and more superficial humeral head arises from the medial supracondylar ridge. The ulnar head is thin and arises from the medial surface of the coronoid process. The median nerve passes through the two heads in order to reach the forearm, and is separated from the ulnar artery by the ulnar head. The muscle inserts onto the lateral surface of the radius distal to supinator, and hence causes pronation when it contracts.

Pronator quadratus 

The anterior interosseus nerve, a branch of the median nerve, innervates this square-shaped 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.

Supinator 

This muscle from the posterior compartment of the forearm is innervated by the deep branch of the radial nerve (arising from the posterior cord, nerve roots C5-T1), which goes on to become the posterior interosseus nerve. It surrounds the proximal part of the radius, and consists of superficial and deep sets of fibers. The deep set arises from the lateral epicondyle of the humerus, the supinator crest of the ulna, the anular ligament and the radial collateral ligament. It inserts onto the lateral, posterior and anterior surfaces of the radius, near to the insertion of pronator teres.

The radial nerve passes down the spiral groove of the humerus, and emerges anterior to the lateral epicondyle, between brachialis and brachioradialis. The nerve then enters the supinator muscle, and divides into the superficial and the deep branch. The latter goes on to innervate the supinator muscle and continues as posterior interosseous nerve.

Biceps brachii 

The musculocutaneous nerve innervates this muscle. The long head arises from the supraglenoid tubercle of the scapula, and the short head arises from the coracoid process. The tendon of the muscle inserts onto the radial tuberosity. The muscle also expands out as the bicipital aponeurosis, which attaches to the shaft of the ulna. Biceps brachii acts primarily as an elbow flexor, and secondarily as a supinator. It is able to supinate when the elbow is flexed. When the elbow is fully extended, supinator performs the action.

Brachioradialis 

This muscle is innervated by the radial nerve. It arises from the lateral supracondylar ridge and lateral intermuscular septum of the arm. The muscle inserts onto the radial tuberosity. As the muscle crosses the elbow joint, anterior to the joint line, it acts as an elbow flexor, and a semi-pronator of the forearm. When the musculocutaneous nerve is damaged, the brachioradialis muscle still enables elbow flexion due to its innervation from the radial nerve. It flexes best when the forearm is in mid-position between supination and pronation. When the elbow is flexed, the brachioradialis semi-pronates the forearm.

Take this integrated quiz in different difficulty levels to test your knowledge on the movements of the body.