Extensor Digitorum Longus: Origin, Insertion, Nerve, Action & Foot Drop

The Extensor Digitorum Longus (EDL) is a pennate muscle located in the anterior compartment of the leg. As its name implies, it is the primary "long" extensor of the toes. It sits laterally to the Tibialis Anterior and is a key muscle for clearing the foot from the ground during walking.

[Image of Extensor Digitorum Longus muscle anatomy]

Quick Anatomy Snapshot

Origin (Proximal)	Lateral Condyle of the Tibia, proximal 3/4 of the anterior surface of the Fibula, and the Interosseous Membrane.
Insertion (Distal)	Splits into 4 tendons inserting on the Middle and Distal phalanges of the Lateral 4 Toes (via dorsal digital expansions).
Nerve Supply	Deep Peroneal (Fibular) Nerve (L5, S1).
Blood Supply	Anterior Tibial Artery.
Primary Actions	Toe Extension: Extends the MTP, PIP, and DIP joints of toes 2-5. Dorsiflexion: Lifts the foot at the ankle joint. Eversion: Weakly assists in turning the sole of the foot outward.

Deep Dive: The "Four-Tendon" Split

The EDL is unique because it starts as a single muscle belly but drastically changes at the ankle.

1. Passing the Retinaculum

The muscle travels down the leg and passes under the Superior and Inferior Extensor Retinacula. These fibrous bands act like a strap, preventing the tendons from "bowstringing" (popping out) when you flex your ankle.

2. The Extensor Hood Mechanism

Just like the fingers in the hand, the tendons of the EDL do not simply attach to one bone. On the dorsal surface of the toes, they form a triangular aponeurosis called the Extensor Expansion (or Dorsal Hood).
• Central Slip: Attaches to the Middle Phalanx.
• Lateral Slips: Attach to the Distal Phalanx.
This allows the muscle to extend the toes at all three joints (MTP, PIP, DIP).

Physio Corner: Clinical Relevance

💪 Functional Fact: During the "Swing Phase" of walking (when your leg is in the air), the EDL contracts to lift the toes and foot. This prevents your toes from dragging on the ground or tripping you.

Palpation

Ask the patient to extend (lift) their toes while keeping the heel on the ground. You will see four distinct tendons pop up on the top of the foot. Follow these tendons up past the ankle; the muscle belly is found in the upper lateral leg, just lateral to the shin bone (Tibia).

⚠️ Clinical Pathology: Foot Drop & Shin Splints
Foot Drop: Damage to the Deep Peroneal Nerve paralyzes the EDL (and Tibialis Anterior), causing the foot to slap the ground or drag.
Anterior Shin Splints: Overuse of the EDL (e.g., running downhill) can cause pain and inflammation at its origin on the tibia/interosseous membrane.

Manual Muscle Testing (MMT)

To test the EDL, we focus on the lateral four toes.

Testing Tip: Make sure the ankle is in neutral. If the ankle is fully plantarflexed, the tendons are tight; if fully dorsiflexed, the muscle is shortened.

Step-by-Step Procedure (Oxford Scale)

Grade	Patient Action & Resistance
Grade 3, 4, 5 (Against Resistance)	Position: Sitting or Supine. Ankle in neutral. Action: Patient extends the lateral four toes (lifts them up). Resistance: Applied to the dorsal aspect of the toes (proximal phalanges), pushing down into flexion. Grade 3: Full range against gravity. Grade 4/5: Holds against moderate/max resistance.
Grade 2 (Gravity Eliminated)	Position: Side-lying (rarely needed for toes) or Supine. Action: Patient attempts to extend the toes. Result: Partial or full range of motion without resistance.
Grade 0, 1 (Palpation)	Action: Palpate the tendons on the dorsum of the foot. Cue: "Try to lift your toes." Grade 1: Tendons become taut. Grade 0: No activity.

Frequently Asked Questions

Does EDL move the Big Toe?

No. The Big Toe has its own specific muscle: the Extensor Hallucis Longus (EHL). The EDL only moves toes 2, 3, 4, and 5.

What is the "Fifth Tendon"?

Often, a small part of the EDL separates and inserts onto the base of the 5th Metatarsal rather than the toe. This distinct slip is called the Fibularis (Peroneus) Tertius. It acts as a dorsiflexor and everter.

Why does my shin hurt when I walk fast?

Fast walking requires the EDL and Tibialis Anterior to work hard to lift the foot quickly (dorsiflexion) to prevent tripping. This repetitive eccentric loading can lead to anterior compartment stress or "shin splints."

Test Your Knowledge: EDL Quiz

1. Which nerve supplies the Extensor Digitorum Longus?

2. The EDL inserts into which toes?

3. Besides toe extension, what is the other primary action of EDL?

4. The EDL passes under which structure at the ankle?

5. What anatomical variation is essentially a 5th tendon of the EDL?

6. Where does the EDL originate?

7. Foot Drop is caused by damage to which nerve?

8. The insertion of EDL is via the:

9. During MMT, resistance is applied to the:

10. True or False: EDL assists in Inversion of the foot.

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.