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Pronator teres muscle

The pronator teres muscle is a superficial muscle of the anterior compartment of the forearm. It has two distinct heads—humeral and ulnar—and serves as a primary pronator of the forearm, turning the palm downward. It also contributes to weak flexion at the elbow. The muscle forms the medial border of the cubital fossa and serves as an important anatomical landmark for the median nerve, which passes between its two heads.

Due to its proximity to the median nerve, the pronator teres is clinically significant in pronator teres syndrome, a compression neuropathy of the median nerve.

Synonyms

  • Round pronator

  • Pronator radii teres

Origin, Course, and Insertion

  • Origin:

    • Humeral head: Medial epicondyle of the humerus via the common flexor tendon

    • Ulnar head: Coronoid process of the ulna

  • Course: The fibers from both heads converge obliquely downward and laterally, forming a flat muscle belly that crosses the proximal forearm.

  • Insertion: Middle of the lateral surface of the radius

Tendon Attachments

  • The tendon is broad and flat at insertion, blending with the deep fascia over the radius.

  • Serves as an important attachment site for the deep fascial sheath separating superficial and deep flexor compartments.

Relations

  • Superficial: Skin and antebrachial fascia

  • Deep: Brachialis and flexor digitorum superficialis

  • Medially: Flexor carpi radialis and ulnar head origin

  • Laterally: Brachioradialis and supinator (antagonists)

  • Posteriorly: Median nerve passing between the two heads

  • Anteriorly: Overlies the anterior ulnar recurrent artery and brachial artery bifurcation

Nerve Supply

  • Median nerve (C6–C7) — passes between the two heads and provides direct motor innervation

Arterial Supply

  • Ulnar artery: Muscular branches

  • Radial artery: Small collateral branches near the cubital fossa

  • Anterior ulnar recurrent artery: Supplies the deep portion near the elbow joint

  • Inferior ulnar collateral artery: Contributes small anastomotic twigs to the humeral head

Venous Drainage

  • Companion veins (venae comitantes) of the ulnar and radial arteries drain the muscle

  • These veins empty into the brachial veins, which then drain into the axillary vein

Function

  • Pronation: Rotates the radius medially, turning the palm downward

  • Elbow flexion: Assists the brachialis and biceps brachii in flexing the elbow joint

  • Stabilization: Maintains the position of the proximal radius during pronation

  • Synergy: Works with pronator quadratus for controlled pronation, especially during resisted motion

Clinical Significance

  • Pronator teres syndrome: Median nerve entrapment between the two heads; causes forearm pain, weakness in thumb opposition, and sensory loss in the lateral palm

  • Overuse injury: Common in athletes using repetitive pronation (e.g., golfers, pitchers)

  • Tendinopathy: Inflammation at medial epicondyle origin may accompany medial epicondylitis (“golfer’s elbow”)

  • Surgical importance: Key landmark for median nerve decompression and during forearm flap harvests

MRI Appearance

  • T1-weighted images:

    • Muscle belly: intermediate signal intensity with visible fascicular pattern

    • Tendinous origin and insertion: low signal (dark)

    • Surrounding fat planes: bright, aiding delineation

    • Chronic muscle atrophy: fatty infiltration with increased T1 signal

  • T2-weighted images:

    • Normal muscle: intermediate-to-dark, slightly darker than on T1

    • Tendons: low signal, continuous bands

    • Pathology (strain, edema, tendinitis): bright hyperintense regions within the muscle or at tendon origins

  • STIR:

    • Normal muscle: intermediate-to-dark

    • Pathology: bright hyperintense signal indicating edema, strain, or inflammation

    • Excellent for detecting acute injuries and nerve entrapment changes around the median nerve

  • Proton Density Fat-Saturated (PD FS):

    • Normal: intermediate-to-dark homogeneous signal

    • Pathologic: focal or diffuse bright signal in acute injury or chronic tendinopathy

    • Enhances visualization of perimuscular inflammation or median nerve irritation

  • T1 Fat-Sat Post-Contrast:

    • Normal muscle: mild uniform enhancement

    • Inflamed or fibrotic regions: show patchy or rim enhancement

    • Nerve entrapment or myositis: perineural enhancement and increased vascularity

CT Appearance

Non-Contrast CT:

  • Muscle belly: soft-tissue density in anterior compartment, lateral to flexor carpi radialis

  • Tendinous origin: linear high-density band along the medial epicondyle

  • Chronic tendinopathy: may show subtle calcifications near origin

  • Useful in identifying calcific tendinitis, enthesopathy, or post-traumatic changes

Post-Contrast CT (standard):

  • Muscle enhances homogeneously

  • Inflamed or fibrotic tissue: shows focal enhancement

  • Helps evaluate soft-tissue masses, myositis ossificans, or surgical anatomy in the cubital fossa

MRI image

Pronator teres muscle axial cross sectional anatomy 3T MRI AI enhanced radiology image -img-00000-00000

MRI image

Pronator teres muscle axial cross sectional anatomy 3T MRI AI enhanced radiology image -img-00000-00000_00001

MRI image

Pronator teres muscle axial cross sectional anatomy 3T MRI AI enhanced radiology image -img-00000-00000_00002

MRI image

Pronator teres muscle axial cross sectional anatomy 3T MRI AI enhanced radiology image -img-00000-00000_00003

MRI image

Pronator teres muscle axial cross sectional anatomy 3T MRI AI enhanced radiology image -img-00000-00000_00004