Extensor Digiti Minimi: Origin, Insertion, Action & The "Tea Drinker's" Muscle

The Extensor Digiti Minimi (EDM) is a slender, fusiform muscle of the posterior forearm. It acts as a specialized "accessory" muscle, allowing the little finger (5th digit) to extend independently of the other fingers. It is famously known as the muscle responsible for raising the pinky while drinking tea!

[Image of Extensor Digiti Minimi muscle anatomy]

Quick Anatomy Snapshot

Origin (Proximal)	Lateral Epicondyle of the Humerus (via the Common Extensor Tendon).
Insertion (Distal)	Extensor Expansion (Dorsal Hood) of the 5th Digit (Little Finger).
Nerve Supply	Posterior Interosseous Nerve (Deep branch of Radial Nerve) - C7, C8.
Blood Supply	Posterior Interosseous Artery.
Primary Actions	Finger Extension: Extends the MCP, PIP, and DIP joints of the little finger. Wrist Extension: Weakly assists in wrist extension and ulnar deviation.

Deep Dive: The "Pinky Specialist"

While the Extensor Digitorum sends a tendon to the little finger, it is usually weak or absent. The EDM provides the main power.

1. The Fifth Compartment

The Extensor Digiti Minimi is anatomically distinct at the wrist. While the main extensor tendons (ED) travel in the 4th dorsal compartment, the EDM travels alone (or with a split tendon) through the 5th Dorsal Compartment. This separation allows for independent movement.

2. The Double Tendon

It is very common for the EDM to split into two separate tendons (a double slip) as it travels down the hand to the pinky. This anatomical variation is normal and can often be seen on the back of the hand when the pinky is extended vigorously.

Physio Corner: Clinical Relevance

💪 Functional Fact: Try extending just your ring finger; it's difficult. Now try extending just your pinky; it's easy! This is because the pinky has the EDM, while the ring finger is tethered by the juncturae tendinum of the Extensor Digitorum.

Palpation

Ask the patient to make a fist and then extend only the little finger. Palpate the ulnar side of the posterior forearm. You will feel the slender muscle belly of the EDM just medial to the larger Extensor Digitorum and lateral to the Extensor Carpi Ulnaris.

⚠️ Clinical Pathology: Wartenberg's Sign
This is a sign of Ulnar Nerve Palsy. The little finger rests in an abducted position (pulled away from the ring finger). Why? The weak ulnar-innervated Palmar Interosseous cannot adduct the finger, so the unopposed pull of the Extensor Digiti Minimi (Radial nerve) pulls the finger into extension and abduction.

Manual Muscle Testing (MMT)

We test the isolated extension of the 5th digit.

Testing Tip: Stabilize the wrist in neutral. If the wrist is fully flexed, the extensor mechanism is too tight; if fully extended, it is too loose.

Step-by-Step Procedure (Oxford Scale)

Grade	Patient Action & Resistance
Grade 3, 4, 5 (Against Resistance)	Position: Forearm pronated, wrist neutral, fingers flexion (fist). Action: Patient extends the little finger (lifts the knuckle/MCP joint). Resistance: Applied at the dorsal aspect of the proximal phalanx of the pinky, pushing down into flexion. Grade 3: Full range against gravity. Grade 4/5: Holds against light/moderate resistance.
Grade 2 (Gravity Eliminated)	Position: Forearm in neutral (mid-position), resting on ulnar border. Action: Patient extends the little finger horizontally. Result: Full range of motion.
Grade 0, 1 (Palpation)	Action: Palpate the tendon over the 5th metacarpal. Cue: "Try to lift your pinky." Grade 1: Tendon tension felt. Grade 0: No activity.

Frequently Asked Questions

Is EDM part of the Extensor Digitorum?

No. It is a separate muscle with its own belly and synovial sheath (5th compartment). However, its tendon usually joins the Extensor Digitorum tendon at the knuckle to form the extensor hood.

Does it abduct the finger?

Yes, slightly. Because its tendon runs on the ulnar side of the joint, extension often comes with a slight abduction component (moving the pinky away from the hand).

Can you have a missing EDM?

Rarely. It is more common to have extra slips or doubled tendons. Absence of the EDM is extremely rare and would result in the inability to extend the pinky independently.

Test Your Knowledge: EDM Quiz

1. Which nerve supplies the Extensor Digiti Minimi?

2. The EDM tendon passes through which dorsal compartment?

3. Where does the EDM insert?

4. Wartenberg's Sign involves the little finger being stuck in:

5. Where does the EDM originate?

6. The EDM allows for which specific movement?

7. Which muscle lies medial to the EDM in the forearm?

8. Besides extension, the EDM assists in:

9. To test MMT Grade 5, resistance is applied to:

10. True or False: The EDM usually has two tendon slips.

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.
• Magee, D. J. (2014). Orthopedic Physical Assessment. 6th ed. Elsevier.