Anconeus: Origin, Insertion, Action, Nerve & Clinical Relevance

The Anconeus is a small, triangular muscle located at the posterior aspect of the elbow joint. While often overshadowed by the massive Triceps Brachii, the Anconeus is clinically significant as a dynamic stabilizer of the elbow and a source of lateral elbow pain.

[Image of Anconeus muscle anatomy]

Quick Anatomy Snapshot

Origin (Proximal)	Posterior surface of the Lateral Epicondyle of the Humerus.
Insertion (Distal)	Lateral surface of the Olecranon process and the superior part of the posterior Ulna.
Nerve Supply	Radial Nerve (C7, C8).
Blood Supply	Deep Brachial Artery (Middle Collateral branch) and Recurrent Interosseous Artery.
Primary Actions	Extension: Assists the Triceps in extending the forearm. Stabilization: Stabilizes the ulna during pronation and supination. Capsule Protection: Pulls the synovial capsule out of the joint during extension.

Deep Dive: The "Fourth Head" of the Triceps

Although considered a separate muscle, the Anconeus is functionally continuous with the Triceps Brachii.

1. The Capsule Protector

As you snap your elbow straight (terminal extension), the joint capsule can become pinched in the olecranon fossa. The Anconeus attaches directly to the capsule and pulls it taut and out of the way, preventing painful impingement.

2. The Rotary Stabilizer

While the Triceps does the heavy lifting for extension, the Anconeus works to abduct the ulna slightly and stabilize the joint during forearm rotation (pronation and supination), acting as an active collateral ligament.

Physio Corner: Clinical Relevance

💪 Functional Fact: The Anconeus is often called the "tea drinker's muscle" (jokingly) or compared to a waiter carrying a tray, because it stabilizes the extended elbow while the forearm rotates.

Palpation

Locate the olecranon (point of the elbow) and the lateral epicondyle. Place your finger in the triangular soft spot between these two bony landmarks. Ask the patient to extend their elbow against resistance. The Anconeus will pop up as a firm triangle just lateral to the olecranon.

⚠️ Clinical Pathology: Tennis Elbow Mimic
Pain in the lateral elbow is almost always diagnosed as "Tennis Elbow" (Extensor Carpi Radialis Brevis tendinopathy). However, trigger points or strains in the Anconeus can refer pain to the exact same spot. If treatment for tennis elbow isn't working, check the Anconeus!

Manual Muscle Testing (MMT)

The Anconeus is tested simultaneously with the Triceps Brachii as it is impossible to isolate it fully.

Testing Tip: Palpate the Anconeus specifically during extension to ensure it is firing, rather than just relying on the Triceps tendon.

Step-by-Step Procedure (Oxford Scale)

Grade	Patient Action & Resistance
Grade 3, 4, 5 (Against Gravity)	Position: Prone (face down) with arm abducted to 90° and forearm hanging off table (elbow flexed). Action: Patient extends the elbow until the arm is straight. Resistance: Applied at the distal forearm, pushing into flexion. Grade 3: Full extension against gravity. Grade 4/5: Holds against strong resistance.
Grade 2 (Gravity Eliminated)	Position: Sitting, arm supported on table at shoulder height (90° abduction), elbow flexed. Action: Patient slides arm along table into extension. Result: Full range of motion.
Grade 0, 1 (Palpation)	Action: Palpate lateral to the olecranon. Cue: "Try to straighten your arm." Grade 1: Triangle of muscle tightens. Grade 0: No activity.

Frequently Asked Questions

Is Anconeus part of the Triceps?

Functionally, yes. Anatomically, it is separated by a distinct fascial plane, but many anatomists consider it a "fourth head" of the triceps group.

What is the "Anconeus Epitrochlearis"?

This is a rare anatomical variant muscle found on the medial side of the elbow (not lateral). If present, it can compress the Ulnar nerve, causing Cubital Tunnel Syndrome.

Does it pronate the arm?

No. While it stabilizes the ulna during pronation, it does not actively rotate the radius over the ulna. Its fibers run obliquely to extend and abduct the ulna.

Test Your Knowledge: Anconeus Quiz

1. What is the origin of the Anconeus?

2. Which nerve supplies the Anconeus?

3. What shape is the Anconeus muscle?

4. The Anconeus prevents impingement of what structure?

5. Where does the Anconeus insert?

6. Anconeus pain is most often confused with:

7. The Anconeus is located in which compartment?

8. Which muscle is the primary agonist for elbow extension?

9. To palpate the Anconeus, you should feel:

10. True or False: The Anconeus is present in everyone.

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.
• Brukner, P., & Khan, K. (2017). Clinical Sports Medicine. 5th ed. McGraw-Hill Education.