Abductor Digiti Minimi (Hand): Origin, Insertion, Nerve Supply, Action & MMT

The Abductor Digiti Minimi (ADM) of the hand is the most superficial muscle of the hypothenar eminence (the fleshy pad on the pinky side of your palm). It forms the medial border of the palm and is the primary muscle responsible for spreading the little finger.

[Image of Abductor Digiti Minimi Hand anatomy]

Quick Anatomy Snapshot

Origin (Proximal)	Pisiform bone, Tendon of the Flexor Carpi Ulnaris, and the Pisohamate ligament.
Insertion (Distal)	Ulnar (medial) side of the base of the Proximal Phalanx of the 5th finger and the dorsal extensor expansion.
Nerve Supply	Deep Branch of Ulnar Nerve (C8, T1).
Blood Supply	Ulnar Artery (Deep palmar branch).
Primary Actions	Abduction: Moves the 5th finger away from the 4th finger. Flexion: Assists in flexion of the proximal phalanx at the MCP joint.

Deep Dive: The Hypothenar Group

The hypothenar eminence consists of three muscles: Abductor Digiti Minimi, Flexor Digiti Minimi Brevis, and Opponens Digiti Minimi. The ADM is the most prominent and superficial of the group.

1. The "Tea Drinker's" Muscle

Historically, extending and abducting the little finger while holding a teacup was considered a sign of etiquette. The Abductor Digiti Minimi is the sole muscle responsible for this specific "polite" posture.

2. Relationship with Flexor Carpi Ulnaris

The ADM is unique because it partly originates from the tendon of another muscle, the Flexor Carpi Ulnaris (FCU). This means that tension in the FCU can stabilize the pisiform bone, giving the ADM a solid base to pull from.

Physio Corner: Clinical Relevance

💪 Functional Fact: While small, this muscle is crucial for power grip. When you grip a large object (like a thick water bottle or hammer), the ADM locks the 5th finger around the object to prevent it from slipping out the ulnar side of the hand.

Palpation

Rest the hand palm up. Ask the patient to spread their little finger wide. Palpate the ulnar (medial) edge of the palm. The ADM forms the distinct fleshy border of the hand, running from the pisiform bone to the base of the pinky.

⚠️ Clinical Pathology: Ulnar Nerve Palsy
Because the ADM is innervated by the Ulnar nerve, atrophy (wasting) of the hypothenar eminence is a hallmark sign of ulnar nerve entrapment (e.g., in Guyon's Canal or Cubital Tunnel). This results in a flattened palm and inability to spread the pinky.

Manual Muscle Testing (MMT)

We test the ability of the muscle to move the finger away from the midline of the hand.

Testing Tip: The midline of the hand is the 3rd digit (middle finger). Moving the pinky away from the ring finger is abduction.

Step-by-Step Procedure (Oxford Scale)

Grade	Patient Action & Resistance
Grade 3, 4, 5 (Against Resistance)	Position: Hand resting on a table, palm up (supinated). Action: Patient abducts the little finger (moves it away from the ring finger). Resistance: Applied at the medial side of the proximal phalanx, pushing the finger inward toward the ring finger. Grade 3: Full range against gravity/friction. Grade 4/5: Holds against strong resistance.
Grade 2 (Gravity Eliminated)	Position: Hand resting on ulnar border (neutral), or flat on table if friction is negligible. Action: Patient attempts to spread the pinky. Result: Full range of motion.
Grade 0, 1 (Palpation)	Action: Palpate the hypothenar eminence on the ulnar border. Cue: "Try to pull your pinky out." Grade 1: Trace contraction felt. Grade 0: No activity.

Frequently Asked Questions

Does it have an insertion on the extensor hood?

Yes. Some fibers insert into the dorsal extensor expansion. This allows the ADM to assist in extending the interphalangeal joints of the little finger, similar to the interossei muscles.

What is Wartenberg's Sign?

This is a clinical sign of ulnar nerve neuropathy where the little finger rests in a position of abduction. It occurs because the Palmar Interossei (adductors) are weak, but the Extensor Digiti Minimi (innervated by Radial nerve) is unopposed and pulls the finger slightly out.

Is the Pisiform a sesamoid bone?

Yes. The pisiform is a sesamoid bone embedded within the tendon of the Flexor Carpi Ulnaris. Since the ADM originates here, the stability of the wrist affects the efficiency of the ADM.

Test Your Knowledge: ADM Hand Quiz

1. What is the primary origin of the Abductor Digiti Minimi (Hand)?

2. Which nerve supplies the ADM?

3. The ADM is part of which muscle group?

4. Which muscle tendon acts as an anchor for the ADM origin?

5. Where does the ADM insert?

6. Besides abduction, what other action does ADM assist with?

7. Atrophy of the hypothenar eminence suggests damage to:

8. The ADM forms the ________ border of the palm.

9. To test MMT Grade 5, where do you apply resistance?

10. True or False: The ADM is deeper than the Flexor Digiti Minimi Brevis.

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.