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Pronator teres muscle (ulnar head)

The ulnar head of the pronator teres muscle is the smaller and deeper portion of the pronator teres, one of the major muscles of the anterior (flexor) compartment of the forearm. It plays an important role in forearm pronation and elbow flexion, working synergistically with the pronator quadratus and biceps brachii.

While the humeral head originates from the medial epicondyle of the humerus, the ulnar head arises from the coronoid process of the ulna. The two heads converge obliquely toward the lateral side of the forearm to form a common tendon inserting on the lateral surface of the radius. The median nerve passes between the humeral and ulnar heads, making this region a key site for pronator syndrome or median nerve entrapment.

Synonyms

  • Ulnar head of pronator teres

  • Deep head of pronator teres

Origin, Course, and Insertion

  • Origin: Medial aspect of the coronoid process of the ulna, just inferior to the trochlear notch

  • Course: Fibers pass obliquely laterally and distally, deep to the humeral head, blending with it in the mid-forearm

  • Insertion: Lateral surface of the radius, at its midshaft, roughened area just distal to the supinator insertion

Relations

  • Anteriorly: Superficial fascia and median cubital vein

  • Posteriorly: Ulnar head lies over the ulnar tuberosity and brachialis tendon

  • Laterally: Brachioradialis and supinator muscles near the radial insertion

  • Medially: Flexor digitorum superficialis and humeral head of pronator teres

  • Deep: Ulnar artery and anterior ulnar recurrent artery course near its origin

Nerve Supply

  • Median nerve (C6–C7), branch of the brachial plexus

  • The median nerve passes between the humeral and ulnar heads, giving off small motor branches within the muscle substance

Arterial Supply

  • Ulnar artery – primary supply via anterior ulnar recurrent branch

  • Radial artery – minor collateral branches in distal region

  • Inferior ulnar collateral artery (from brachial artery) – small contributions near the elbow

Venous Drainage

  • Venae comitantes of the ulnar and radial arteries

  • Drain proximally into the brachial veins, then into the axillary vein

Function

  • Forearm pronation: Rotates the radius medially over the ulna

  • Elbow flexion assistance: Aids in flexion when the forearm is pronated

  • Dynamic stabilizer: Helps stabilize the proximal radioulnar joint during pronation-supination

  • Synergistic role: Works with pronator quadratus during controlled pronation

Clinical Significance

  • Median nerve entrapment (Pronator Syndrome): The ulnar head forms a fibrous arch through which the median nerve passes; hypertrophy or tightness here can compress the nerve, causing forearm pain and paresthesia in the lateral hand.

  • Muscle strain or tendinopathy: May occur in athletes or repetitive pronation activities (e.g., throwing, racquet sports).

  • Iatrogenic injury: Possible during forearm or elbow surgeries.

  • Compartment involvement: Can be affected in anterior forearm compartment syndrome.

  • Imaging importance: MRI can identify muscle hypertrophy, denervation, or edema related to nerve entrapment.

MRI Appearance

  • T1-weighted images:

    • Muscle belly: intermediate signal intensity, with clear fascicular pattern

    • Fat planes between humeral and ulnar heads appear bright

    • Median nerve: intermediate signal, running between the two heads

    • Chronic atrophy or fatty replacement shows increased intramuscular signal intensity

  • T2-weighted images:

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

    • Tendon and fascia: low signal (dark)

    • Pathology: bright hyperintense signal in muscle or tendon (strain, partial tear, inflammation)

    • Median nerve edema: hyperintense round or linear signal between muscle heads

  • STIR:

    • Normal muscle: intermediate-to-dark signal

    • Pathologic muscle or perineural inflammation: bright hyperintense signal

    • Excellent for detecting median nerve entrapment or perimuscular edema

  • Proton Density Fat-Saturated (PD FS):

    • Normal muscle: intermediate-to-dark, uniform signal intensity

    • Muscle strain, denervation, or tendinitis: focal bright hyperintensity within the muscle

    • Enhances detection of fibrous band entrapments and subtle myofascial tears

  • T1 Fat-Sat Post-Contrast:

    • Normal: mild homogeneous enhancement

    • Pathologic: enhancement along the perineural or perimuscular regions in cases of inflammation

    • Chronic changes: minimal enhancement with fibrotic low-signal bands

CT Appearance

Non-Contrast CT:

  • Muscle: soft-tissue density along anteromedial forearm

  • Clear separation of humeral and ulnar heads visible in high-resolution scans

  • Chronic hypertrophy or fibrosis may appear as focal soft-tissue thickening near the coronoid process

  • No distinct visualization of fascial architecture without contrast

Post-Contrast CT (standard):

  • Normal muscle: homogeneous enhancement

  • Inflammatory or vascularized lesions show increased local enhancement

  • Useful for identifying post-traumatic scarring, muscle laceration, or postoperative changes

  • Can delineate perineural enhancement in median nerve entrapment cases

MRI images

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

MRI images

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

MRI images

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