Pronator Teres: Origin, Insertion, Nerve, Action & Pronator Syndrome

The Pronator Teres is a superficial muscle of the anterior forearm. As its name suggests, it is a round (teres) muscle that turns the palm down (pronation). It crosses the elbow joint obliquely and serves as an important boundary for the Cubital Fossa.

[Image of Pronator Teres muscle anatomy]

Quick Anatomy Snapshot

Origin (Proximal)	1. Humeral Head: Medial Epicondyle of the Humerus (Common Flexor Tendon). 2. Ulnar Head: Coronoid Process of the Ulna.
Insertion (Distal)	Middle of the lateral surface of the shaft of the Radius (Pronator Tuberosity).
Nerve Supply	Median Nerve (C6, C7).
Blood Supply	Ulnar Artery and Anterior Ulnar Recurrent Artery.
Primary Actions	Pronation: Turns the palm downwards (Powerful pronator). Elbow Flexion: Weakly assists in bending the elbow.

Deep Dive: The Nerve Trap

The Pronator Teres has two heads (Humeral and Ulnar), and their relationship with the nervous system is clinically critical.

1. The Median Nerve Sandwich

The Median Nerve passes directly between the two heads of the Pronator Teres as it travels down the forearm. Because the nerve runs through the muscle belly, hypertrophy or spasm of the muscle can compress the nerve.

2. The Cubital Fossa Border

The Pronator Teres forms the Medial Border of the Cubital Fossa (the triangular depression in front of the elbow). The Brachioradialis forms the lateral border, and an imaginary line between the epicondyles forms the base.

Physio Corner: Clinical Relevance

💪 Functional Fact: While the Pronator Quadratus initiates pronation, the Pronator Teres is recruited for Power and Speed. You use this muscle heavily when turning a stubborn doorknob, using a screwdriver, or arm wrestling.

Palpation

Shake hands with the patient. Ask them to try to turn their palm down (pronate) while you resist. The Pronator Teres will pop up diagonally across the upper forearm, running from the medial elbow towards the middle of the radius.

⚠️ Clinical Pathology: Pronator Teres Syndrome
Compression of the Median Nerve between the two heads of the muscle.
Symptoms: Pain in the proximal forearm and numbness in the thumb/index/middle fingers (similar to Carpal Tunnel).
Distinction: In Pronator Syndrome, sensation in the palm is lost (because the palmar cutaneous branch is affected), whereas in Carpal Tunnel, the palm sensation is spared.

Manual Muscle Testing (MMT)

To test the Pronator Teres specifically, we test pronation with the elbow extended (though standard testing often uses 90 degrees flexion).

Testing Tip: To isolate the Pronator Teres from the Pronator Quadratus, apply resistance during rapid or high-force pronation. The Quadratus works alone during slow, unresisted movement.

Step-by-Step Procedure (Oxford Scale)

Grade	Patient Action & Resistance
Grade 3, 4, 5 (Against Resistance)	Position: Sitting or Supine. Elbow flexed to 90°, forearm fully supinated (palm up) or neutral. Action: Patient turns the palm down (Pronation) into the table. Resistance: Applied at the distal radius (wrist), pushing the hand back into Supination. Grade 3: Full range against gravity. Grade 4/5: Holds against strong resistance.
Grade 2 (Gravity Eliminated)	Position: Sitting with shoulder flexed to 90° and elbow flexed to 90° (arm supported on table, hand pointing up). Action: Patient rotates the forearm to face the palm outward. Result: Full range of motion.
Grade 0, 1 (Palpation)	Action: Palpate medial to the Biceps tendon in the cubital fossa. Cue: "Try to turn your palm down." Grade 1: Muscle contraction felt. Grade 0: No activity.

Frequently Asked Questions

What is the difference between Pronator Teres and Pronator Quadratus?

Pronator Teres: Located at the elbow, superficial, used for power and speed, also flexes the elbow.
Pronator Quadratus: Located at the wrist, deep, acts as the primary initiator of pronation and stabilizer of the DRUJ.

Is it involved in Golfer's Elbow?

Yes. Because it originates from the Medial Epicondyle via the Common Flexor Tendon, overuse can contribute to Medial Epicondylitis (Golfer's Elbow).

Does it cross the wrist joint?

No. It inserts into the middle of the radius. Therefore, it has no action on the wrist joint (unlike the Flexor Carpi muscles).

Test Your Knowledge: Pronator Teres Quiz

1. Which nerve passes between the two heads of the Pronator Teres?

2. Where does the Pronator Teres insert?

3. What is the secondary action of the Pronator Teres?

4. Pronator Syndrome differs from Carpal Tunnel Syndrome by:

5. The Pronator Teres forms the medial border of the:

6. Where does the Ulnar head of Pronator Teres originate?

7. Which muscle initiates pronation?

8. Which compartment of the forearm is Pronator Teres in?

9. To stretch the Pronator Teres, you should:

10. True or False: Pronator Teres crosses the wrist joint.

References

• Moore, K. L., Dalley, A. F., & Agur, A. M. R. (2018). Clinically Oriented Anatomy. 8th ed. Philadelphia: Wolters Kluwer.
• Standring, S. (2016). Gray's Anatomy: The Anatomical Basis of Clinical Practice. 41st ed. Elsevier.
• Kendall, F. P. (2005). Muscles: Testing and Function, with Posture and Pain. 5th ed. Lippincott Williams & Wilkins.