Flexor Digiti Minimi Brevis (Hand): Origin, Insertion, Nerve & Action

The Flexor Digiti Minimi Brevis (FDMB) of the hand is one of the three muscles that make up the Hypothenar Eminence (the fleshy pad on the pinky side of the palm). It is situated lateral to the abductor muscle and is responsible for flexing the little finger at the knuckle.

[Image of Flexor Digiti Minimi Brevis Hand anatomy]

Quick Anatomy Snapshot

Origin (Proximal)	Hook of Hamate and the Flexor Retinaculum (Transverse Carpal Ligament).
Insertion (Distal)	Medial (Ulnar) side of the base of the Proximal Phalanx of the 5th digit (Little Finger).
Nerve Supply	Deep Branch of Ulnar Nerve (C8, T1).
Blood Supply	Deep Palmar Branch of Ulnar Artery.
Primary Actions	Flexion: Flexes the 5th finger at the Metacarpophalangeal (MCP) joint. Opposition: Weakly assists in bringing the 5th finger toward the thumb.

Deep Dive: The "Brevis" without a "Longus"

In the hand, we use the term "Brevis" (short) for this muscle, even though there is no "Flexor Digiti Minimi Longus" in the forearm.

1. The Missing Longus

The flexion of the little finger is powered by three muscles:
• Flexor Digitorum Profundus: Flexes the DIP joint (Tip).
• Flexor Digitorum Superficialis: Flexes the PIP joint (Middle).
• Flexor Digiti Minimi Brevis: Flexes the MCP joint (Knuckle).
Unlike the thumb (which has a separate Flexor Pollicis Longus), the pinky shares the long flexors with the other fingers.

2. Hypothenar Anatomy

The FDMB lies lateral (radial) to the Abductor Digiti Minimi. The ulnar nerve and artery pass deep to these muscles as they exit Guyon's Canal, making the hypothenar muscles important landmarks for neurovascular surgery.

Physio Corner: Clinical Relevance

💪 Functional Fact: This muscle is crucial for power grip on the ulnar side of the hand (e.g., holding a hammer or golf club). It locks the MCP joint of the pinky into flexion, creating a stable backstop for the tool handle.

Palpation

Locate the hypothenar eminence. The FDMB is located just lateral to the ulnar border of the hand (where the Abductor sits). Ask the patient to flex their little finger at the knuckle while keeping the IP joints straight. You can feel the muscle belly tense up in the center of the hypothenar pad.

⚠️ Clinical Pathology: Hypothenar Hammer Syndrome
Repetitive trauma to the hypothenar eminence (using the hand as a hammer) can damage the Ulnar Artery as it passes near the Hook of Hamate (the origin of FDMB). This can cause thrombosis or aneurysm, leading to pain and coldness in the ring and little fingers.

Manual Muscle Testing (MMT)

Testing the intrinsic flexion of the little finger.

Testing Tip: Ensure the patient flexes only at the knuckle (MCP). If they curl the tip of the finger, they are using the long flexors (FDP/FDS).

Step-by-Step Procedure (Oxford Scale)

Grade	Patient Action & Resistance
Grade 3, 4, 5 (Against Resistance)	Position: Forearm supinated (palm up), wrist neutral. Action: Patient flexes the little finger at the MCP joint while keeping the IP joints extended. Resistance: Applied to the volar (palm) surface of the Proximal Phalanx of the 5th finger, pushing down into extension. Grade 3: Full range against gravity. Grade 4/5: Holds against resistance.
Grade 0, 1 (Palpation)	Action: Palpate the hypothenar eminence just lateral to the ulnar border. Cue: "Try to bend your pinky knuckle." Grade 1: Trace contraction felt. Grade 0: No activity.

Frequently Asked Questions

Is it sometimes fused with other muscles?

Yes. The Flexor Digiti Minimi Brevis is often blended with the Abductor Digiti Minimi. In some people, it may be absent or very difficult to distinguish from the Abductor.

Does it originate from the Pisiform?

No. The Abductor Digiti Minimi originates from the Pisiform. The Flexor originates more distally from the Hook of Hamate.

What is its relation to Guyon's Canal?

The FDMB originates from the Hook of Hamate, which forms the lateral wall of Guyon's Canal. Compression here affects the deep branch of the ulnar nerve, potentially paralyzing this muscle.

Test Your Knowledge: Hand FDMB Quiz

1. What is the origin of the Flexor Digiti Minimi Brevis (Hand)?

2. Which nerve supplies the FDMB?

3. Where does the FDMB insert?

4. What is the primary action of the FDMB?

5. Where is the FDMB located relative to the Abductor Digiti Minimi?

6. Hypothenar Hammer Syndrome involves damage to which artery?

7. To test FDMB, where do you apply resistance?

8. Why is it called "Brevis"?

9. Which muscle lies deep to the FDMB?

10. True or False: The FDMB helps cup the hand.

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.