Anatomy of the Supinator

Courtesy : Prof Nabile Ebraheim, University of Toledo, Ohio, USA

ANATOMY OF THE SUPINATOR MUSCLE

Which muscles supinate the forearm?

• Biceps muscle(musculocutaneous nerve).
• Supinator muscle (radial nerve).

The function of the supinator muscle (along with the biceps) is to supinate the forearm or rotate the radius to turn the palm anteriorly.

Which muscle pronates the forearm?

• Pronator teres muscle (median nerve)
• Pronator quadratus muscle (median nerve)

The function of the pronator teres is to pronate the forearm(along with the pronator quadratus) so that the palm turns posterior.

Elbow range of motion supination/pronation:

• Normal range of pronation /supination is between 80°-90°.
• Normal flexion of the elbow is between 0°-150° degrees of motion.
• Functional range of motion is from 30°to 130° degrees of flexion and 55° degrees of supination/ pronation

Nerves & the area of entrapment.

1. The median nerve passes between the two heads of the pronator teres muscle. This may be an area of entrapment for the median nerve during forearm rotation.

2. The deep branch of the radial nerve passes through the supinator muscle. At this area the nerve can become entrapped.

Origin &Insertion

• The origin of the supinator muscle comes from the lateral epicondyle of the humerus, supinator crest of ulna, the radial collateral ligament and the annular ligament.
• The supinator muscle curves around the upper third of the radius.
• It inserts into the lateral, posterior and anterior surfaces of the proximal ? of radius

INNERVATION

• The supinator muscle is a broad muscle in the posterior compartment of the forearm supplied by the posterior interosseous nerve, which is a continuation of the deep branch of the radial nerve ( C5, C6).
• The radial nerve divides into deep and sensory superficial branches just proximal to supinator muscle.
• The posterior interosseous nerve(deep) gives a branch to the supinator muscle just before it enters the muscle.
• The posterior interosseous nerve (deep) enters the extensor compartment of the forearm through the supinator muscle.
• The area in which the posterior interosseous nerve passes through is called the ‘ ARCADE OF FROHSE’ and this area is often a site for entrapment of the posterior interosseous nerve.
• The posterior interosseous nerve does not supply cutaneous sensation and is purely a motor nerve.