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

The Abductor Digiti Minimi (ADM) of the foot is the most lateral muscle of the sole. It lies along the outside edge of the foot and is responsible for moving the "baby toe." While its action of spreading the toe seems minor, it plays a vital role in supporting the lateral arch of the foot during walking.

[Image of Abductor Digiti Minimi Foot anatomy]

Quick Anatomy Snapshot

Origin (Proximal)	Lateral and Medial processes of the Calcaneal Tuberosity (Heel bone). Plantar Aponeurosis. Intermuscular septum.
Insertion (Distal)	Lateral side of the base of the Proximal Phalanx of the 5th toe (digiti minimi).
Nerve Supply	Lateral Plantar Nerve (S1, S2). (Specifically the first branch, often involved in Baxter's Neuropathy).
Blood Supply	Lateral Plantar Artery.
Primary Actions	Abduction: Spreads the 5th toe. Flexion: Curls the 5th toe. Stabilization: Supports the Lateral Longitudinal Arch.

Deep Dive: The First Layer

The muscles of the sole of the foot are arranged in four layers. The Abductor Digiti Minimi is located in the First Layer (the most superficial layer), along with the Abductor Hallucis and Flexor Digitorum Brevis.

1. The "Border" Muscle

Because it runs along the entire lateral border of the foot, it acts as a soft-tissue cushion for the fifth metatarsal bone during the stance phase of gait.

2. "Baxter's Nerve" Relation

The first branch of the Lateral Plantar Nerve is often called the "Nerve to the Abductor Digiti Minimi." This nerve runs deep to the heel and can become entrapped, causing heel pain that mimics plantar fasciitis (known as Baxter's Neuropathy).

Physio Corner: Clinical Relevance

💪 Functional Fact: While few people can voluntarily spread their baby toe widely, this muscle is active during the "Heel Strike" to "Mid-Stance" phase of walking to stabilize the foot and resist pronation.

Palpation

Locate the lateral tuberosity of the calcaneus (outer heel). Trace the fleshy muscle belly along the lateral border of the foot towards the 5th toe. It is most easily felt if you ask the patient to forcefully curl or spread their toes.

⚠️ Clinical Pathology: Tailor's Bunion (Bunionette)
While usually a bony deformity of the 5th metatarsal head, tightness or overactivity of the ADM can contribute to the lateral deviation of the 5th toe, exacerbating a "Bunionette."

Manual Muscle Testing (MMT)

Testing this muscle specifically can be tricky as the lateral toes often move together.

Testing Tip: Be gentle! The 5th toe is small and leverage is high.

Step-by-Step Procedure (Oxford Scale)

Grade	Patient Action & Resistance
Grade 3, 4, 5 (Against Resistance)	Position: Supine or Sitting with foot relaxed. Action: Patient abducts (spreads) the 5th toe away from the 4th toe. Resistance: Applied at the lateral aspect of the proximal phalanx, pushing the toe inward (adduction). Grade 3: Full range of motion. Grade 4/5: Holds against resistance.
Grade 2 (Assisted)	Position: Same as above. Action: Patient attempts to spread the toe. Result: Visible movement (partial range) without resistance.
Grade 0, 1 (Palpation)	Action: Palpate the lateral border of the foot. Cue: "Try to pull your little toe out to the side." Grade 1: Trace contraction felt. Grade 0: No activity.

Frequently Asked Questions

Is this muscle the same as in the hand?

Anatomically, they are homologous (equivalents). The ADM in the hand moves the pinky finger, while the ADM in the foot moves the pinky toe. Both are innervated by "ulnar-equivalent" nerves (Ulnar nerve in hand, Lateral Plantar nerve in foot).

What is Baxter's Neuropathy?

It is the entrapment of the inferior calcaneal nerve (first branch of the lateral plantar nerve), which supplies the Abductor Digiti Minimi. It presents as chronic heel pain often mistaken for Plantar Fasciitis.

Does it help form the foot arch?

Yes. By running from the calcaneus to the toes, it acts like a "tie rod" for the Lateral Longitudinal Arch, preventing it from collapsing under weight.

Test Your Knowledge: ADM Foot Quiz

1. In which layer of the plantar foot muscles is the ADM located?

2. What is the nerve supply of the Abductor Digiti Minimi?

3. Where does the ADM insert?

4. Which condition involves the nerve to the ADM?

5. The ADM supports which arch of the foot?

6. What is the primary action of the ADM?

7. The origin of ADM includes the:

8. Which muscle is an antagonist to the ADM?

9. "Bunionette" is a deformity of which joint?

10. To bias the ADM during palpation, you should ask the patient to:

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.