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

The Flexor Digiti Minimi Brevis (FDMB) of the foot is a small intrinsic muscle located on the lateral (pinky) side of the sole. It belongs to the third layer of plantar muscles. It mimics the function of its hand counterpart, controlling the flexion of the little toe.

[Image of Flexor Digiti Minimi Brevis Foot anatomy]

Quick Anatomy Snapshot

Origin (Proximal)	Base of the 5th Metatarsal and the sheath of the Peroneus Longus tendon.
Insertion (Distal)	Lateral side of the base of the Proximal Phalanx of the 5th digit (Little Toe).
Nerve Supply	Lateral Plantar Nerve (Superficial Branch) - S2, S3.
Blood Supply	Lateral Plantar Artery and Digital Arteries.
Primary Actions	Flexion: Flexes the 5th toe at the Metatarsophalangeal (MTP) joint. Stabilization: Supports the Lateral Longitudinal Arch.

Deep Dive: The Third Layer

The plantar muscles of the foot are divided into four layers. The Flexor Digiti Minimi Brevis resides in the 3rd Layer, along with the Flexor Hallucis Brevis and Adductor Hallucis.

1. Relation to Abductor

The FDMB lies medial to the Abductor Digiti Minimi (which is in the 1st layer). These two muscles often appear fused near their insertion, and structurally they work together to stabilize the lateral column of the foot during walking.

2. No "Longus" Counterpart?

Unlike the hand, there is no muscle named "Flexor Digiti Minimi Longus" in the foot. However, the long flexor action is provided by a slip from the Flexor Digitorum Longus. The term "Brevis" is used to distinguish it as the short, intrinsic flexor.

Physio Corner: Clinical Relevance

💪 Functional Fact: This muscle is active during the "Heel Rise" and "Toe Off" phases of gait. It stabilizes the 5th metatarsal against the ground, preventing the foot from rolling outward excessively (supination).

Palpation

Palpate the base of the 5th metatarsal (the bony bump on the outside of the foot). Move your fingers slightly distally and medially into the sole. Ask the patient to curl their little toe. You will feel the muscle contract just deep to the thick plantar pad.

⚠️ Clinical Pathology: 5th Metatarsal Fractures
Because this muscle originates from the base of the 5th metatarsal, an Avulsion Fracture (Jones Fracture or Pseudo-Jones Fracture) in this area can cause pain when this muscle contracts or is stretched.

Manual Muscle Testing (MMT)

We test the flexion of the MTP joint of the little toe.

Testing Tip: Apply resistance to the Proximal Phalanx, not the tip of the toe. Pushing on the tip tests the Long Flexors (FDL), whereas pushing on the proximal phalanx isolates the Intrinsic Flexors (FDMB).

Step-by-Step Procedure (Oxford Scale)

Grade	Patient Action & Resistance
Grade 3, 4, 5 (Against Resistance)	Position: Supine or Sitting. Ankle neutral. Action: Patient flexes the little toe (curls it at the knuckle/MTP). Resistance: Applied beneath the Proximal Phalanx of the 5th toe, pushing up into extension. Grade 3: Full range. Grade 4/5: Holds against resistance.
Grade 0, 1 (Palpation)	Action: Palpate the plantar surface near the 5th metatarsal head. Cue: "Try to curl your little toe." Grade 1: Contraction felt. Grade 0: No activity.

Frequently Asked Questions

Does it attach to the Peroneus Longus?

Yes. The Flexor Digiti Minimi Brevis often takes a partial origin from the fibrous sheath covering the Peroneus Longus tendon as it crosses the sole of the foot.

Does it bend the tip of the toe?

No. It inserts on the Proximal Phalanx, so it only flexes the Metatarsophalangeal (MTP) joint. The flexion of the DIP and PIP joints (tip of the toe) is done by the Flexor Digitorum Longus.

Which arch does it support?

The Lateral Longitudinal Arch. By connecting the 5th metatarsal to the toe, it acts as a dynamic tie-rod for the outer edge of the foot.

Test Your Knowledge: FDMB Quiz

1. Which nerve supplies the Flexor Digiti Minimi Brevis?

2. Which layer of the plantar foot muscles is it in?

3. Where does the FDMB originate?

4. Where does it insert?

5. What joint does the FDMB primarily act upon?

6. The FDMB originates partly from the sheath of which tendon?

7. Which muscle lies medial to the Flexor Digiti Minimi Brevis?

8. Does the FDMB assist in spreading the toes?

9. To test FDMB (intrinsic), resistance is applied to:

10. Which arch does this muscle primarily support?

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.