Extensor Digitorum Brevis: Origin, Insertion, Nerve & "The Foot Bump"

The Extensor Digitorum Brevis (EDB) is the only intrinsic muscle located on the dorsum (top) of the foot. It is a flat, fleshy muscle that is often mistaken for a soft tissue tumor or cyst because of the prominent bump it forms on the outer foot.

[Image of Extensor Digitorum Brevis muscle anatomy]

Quick Anatomy Snapshot

Origin (Proximal)	Superolateral surface of the Calcaneus (Heel bone) and the Inferior Extensor Retinaculum.
Insertion (Distal)	The muscle splits into 4 tendons: 1st (Medial): Inserts on base of Big Toe (often called Extensor Hallucis Brevis). 2nd-4th: Join the Extensor Digitorum Longus tendons of toes 2, 3, and 4.
Nerve Supply	Deep Peroneal Nerve (L5, S1).
Blood Supply	Dorsalis Pedis Artery and Lateral Tarsal Artery.
Primary Actions	Toe Extension: Assists the long extensors in extending the MTP and IP joints of toes 1-4. Note: It does not attach to the 5th toe (pinky).

Deep Dive: The Only Dorsal Muscle

While the sole of the foot is packed with four layers of muscles, the top of the foot has only one: the EDB.

1. Extensor Hallucis Brevis (EHB)

Although anatomically part of the EDB mass, the most medial belly is functionally distinct. It is often named separately as the Extensor Hallucis Brevis. It sends a tendon strictly to the proximal phalanx of the big toe to assist with extension.

2. Missing the Pinky

The EDB provides tendons to the Big Toe and toes 2, 3, and 4. The 5th toe (pinky) relies entirely on the Extensor Digitorum Longus (EDL) coming from the shin for extension. This is a key way to distinguish the two muscles.

Physio Corner: Clinical Relevance

💪 Functional Fact: Because the EDB originates from the lateral side of the foot and pulls diagonally inward, it helps correct the "tracking" of the toes. Without it, the long extensors (EDL) would pull the toes primarily up and out.

Palpation

Ask the patient to extend their toes against resistance. Locate the Sinus Tarsi (the soft depression just in front of the lateral ankle bone/malleolus). The fleshy belly of the EDB will pop up prominently in this space. It feels soft and squishy, which is why patients often panic and think it's a ganglion cyst.

⚠️ Clinical Pathology: L5 Radiculopathy
The EDB is predominantly innervated by the L5 spinal nerve root. In cases of L5 nerve root compression (e.g., herniated disc), atrophy (wasting) of the EDB is an early and reliable sign. Always compare the size of the "foot bump" on both feet!

Manual Muscle Testing (MMT)

Testing the EDB involves isolating extension without relying solely on the long shin muscles.

Testing Tip: It is difficult to test EDB in isolation from EDL. However, observation is key. If the patient extends toes and you see the distinct muscle belly bulge on the lateral foot, the EDB is active.

Step-by-Step Procedure (Oxford Scale)

Grade	Patient Action & Resistance
Grade 3, 4, 5 (Against Resistance)	Position: Sitting or Supine. Ankle neutral. Action: Patient extends the toes. Resistance: Applied to the dorsal aspect of the toes (2-4), pushing down into flexion. Observation: Look for the muscle belly to contract distal to the lateral malleolus.
Grade 0, 1 (Palpation)	Action: Palpate the muscle belly anterolateral to the lateral malleolus (in front of the ankle bone). Cue: "Try to lift your toes up." Grade 1: Muscle hardens/bulges. Grade 0: No activity (check for L5 pathology).

Frequently Asked Questions

Is the bump on the side of my foot a tumor?

Often, patients mistake the EDB muscle belly for a cyst or tumor because it is soft and prominent. If it contracts and hardens when you wiggle your toes, it's just your muscle!

Why doesn't it go to the little toe?

Evolutionarily, the lateral tendon to the 5th toe has been lost in most humans. The 5th toe is usually moved solely by the long extensor (EDL) and the Abductor Digiti Minimi.

What is the Extensor Hallucis Brevis?

It is essentially the most medial part of the EDB muscle. It is distinct because it inserts separately onto the base of the big toe's proximal phalanx.

Test Your Knowledge: EDB Quiz

1. Where is the Extensor Digitorum Brevis located?

2. Which nerve supplies the EDB?

3. The EDB sends tendons to which toes?

4. Where does the EDB originate?

5. What is the medial part of the EDB often called?

6. Atrophy of the EDB is a clinical sign of damage to which nerve root?

7. The EDB muscle belly is often mistaken for:

8. Which toe does NOT receive an EDB tendon?

9. The EDB tendons join the tendons of which muscle?

10. True or False: EDB is located deep to the plantar fascia.

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.