Peroneus Brevis: Origin, Insertion, Nerve, Action & Ankle Sprains

The Peroneus Brevis (also known as Fibularis Brevis) is a muscle located in the lateral compartment of the lower leg. It lies deep to the Peroneus Longus and is shorter ("Brevis") than its counterpart. It is a crucial evertor of the foot and a primary stabilizer against inversion sprains.

[Image of Peroneus Brevis muscle anatomy]

Quick Anatomy Snapshot

Origin (Proximal)	Distal 2/3 of the lateral surface of the Fibula and adjacent intermuscular septa.
Insertion (Distal)	Tuberosity at the base of the 5th Metatarsal bone (lateral side of the foot).
Nerve Supply	Superficial Peroneal (Fibular) Nerve (L5, S1).
Blood Supply	Peroneal (Fibular) Artery.
Primary Actions	Eversion: Turns the sole of the foot outwards. Plantarflexion: Assists in pointing the foot down (weakly).

Deep Dive: The Lateral Stabilizer

The Peroneus Brevis is often overshadowed by the Longus, but its insertion point makes it clinically notorious.

1. Deep to Longus

The Brevis lies directly underneath the Peroneus Longus. Its tendon travels anterior (in front of) the Longus tendon as they pass behind the lateral malleolus (ankle bone). This relationship is maintained by the peroneal retinacula.

2. The Insertion Site

Unlike the Longus, which dives under the foot to the medial side, the Brevis stops short. It inserts prominently on the styloid process (tuberosity) of the 5th Metatarsal. This bony bump is easily palpable on the outside edge of the foot.

Physio Corner: Clinical Relevance

💪 Functional Fact: The Peroneus Brevis is your first line of defense against a rolled ankle. When your foot starts to invert (roll in) excessively, this muscle contracts reflexively to pull the foot back to neutral (eversion). Weakness here leads to chronic ankle instability.

Palpation

Locate the Lateral Malleolus (outer ankle bone) and the base of the 5th metatarsal (bony bump on outer foot). Ask the patient to evert their foot (turn sole out). You can trace the tendon running directly from the back of the malleolus to the 5th metatarsal.

⚠️ Clinical Pathology: Avulsion Fracture (Pseudo-Jones)
During a severe inversion ankle sprain, the Peroneus Brevis contracts so violently to stop the roll that it can rip a piece of bone off the base of the 5th metatarsal. This is called an Avulsion Fracture (often confused with a Jones fracture, which is slightly more distal).

Manual Muscle Testing (MMT)

To isolate the Peroneals, we test eversion. The Longus and Brevis are usually tested together.

Testing Tip: Test in Plantarflexion to disengage the Tibialis Anterior (which dorsiflexes and inverts) and Extensor Digitorum Longus (which dorsiflexes and everts).

Step-by-Step Procedure (Oxford Scale)

Grade	Patient Action & Resistance
Grade 3, 4, 5 (Against Resistance)	Position: Supine or side-lying. Ankle in plantarflexion. Action: Patient turns the sole of the foot outward (Eversion). Resistance: Applied to the lateral border of the foot, pushing inward (into Inversion and Dorsiflexion). Grade 3: Full range against gravity. Grade 4/5: Holds against strong resistance.
Grade 2 (Gravity Eliminated)	Position: Supine, heel resting on table. Action: Patient slides the forefoot laterally into eversion. Result: Full range of motion.
Grade 0, 1 (Palpation)	Action: Palpate the tendon between the lateral malleolus and the 5th metatarsal. Cue: "Try to turn your foot out." Grade 1: Tendon tension felt. Grade 0: No activity.

Frequently Asked Questions

Is it Peroneus or Fibularis?

Both are correct. "Peroneus" is Greek and "Fibularis" is Latin. The official anatomical terminology (Terminologia Anatomica) prefers Fibularis, but clinicians still widely use Peroneus.

What is the difference between Jones Fracture and Avulsion Fracture?

Avulsion Fracture (Pseudo-Jones): The Peroneus Brevis tendon rips off the tip of the 5th metatarsal tuberosity.
Jones Fracture: A fracture in the meta-diaphyseal junction (about 1.5cm distal to the tuberosity), usually due to stress/loading, not tendon pull. It heals poorly.

Does it support the arch?

Yes, the Lateral Longitudinal Arch. However, the Peroneus Longus is more significant for arch support (Transverse Arch) because it slings underneath the foot.

Test Your Knowledge: Peroneus Brevis Quiz

1. Where does the Peroneus Brevis insert?

2. Which nerve supplies the Peroneus Brevis?

3. What is the primary action of the Peroneus Brevis?

4. The Peroneus Brevis originates from the:

5. The tendon of Brevis runs ______ to the tendon of Longus at the ankle.

6. An Avulsion Fracture of the 5th metatarsal base is often caused by:

7. Which compartment does this muscle belong to?

8. Besides eversion, what is the secondary action?

9. To MMT the Peroneals, you resist:

10. True or False: Peroneus Brevis crosses the sole of the foot to the 1st metatarsal.

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.