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Fibularis Longus Muscle Anatomy

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Origin
  • Superior two-thirds of the lateral surface of the fibula
  • Fibular head
Insertion
  • Base of the first metatarsal
  • Medial cuneiform
Action
  • Eversion of the foot
  • Assists with plantar flexion
Innervation
  • Superficial fibular nerve (superficial peroneal nerve), L5 and S1
Blood Supply
  • Anterior tibial artery
  • Fibular artery (peroneal artery)
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Location & Overview

The fibularis longus, which was previously known as the peroneus longus, is a slender, elongated fusiform muscle located on the lateral aspect of the leg. This muscle is one of the three fibularis muscles, alongside the fibularis tertius and fibularis brevis. At its proximal end, it is superficial to part of the fibularis brevis muscle. The tendons of fibularis longus and brevis run parallel to each other toward the ankle joint, with the longus being more posteriorly placed. However, the pathway differs at the muscle’s distal end. Here, the longus tendon continues beneath the foot, terminating at the base of the first metatarsal. This pathway is in contrast to the fibularis brevis, which attaches to the fifth metatarsal. Its positioning is demonstrated in the images below.[1,2,3]

fibularis longus lateral view
Pictured here, we can see the fibularis longus muscle from a lateral view.
fibularis longus anterolateral view
Pictured here, we can see the fibularis longus muscle from an anterolateral view.
fibularis longus seen from below
Pictured here, we can see the fibularis longus muscle from a posterior and somewhat inferior view.
fibularis longus underneath foot
Pictured here, we can see the fibularis longus muscle’s distal tendon underneath the foot.
three fibularis muscles (aka peroneus muscles), fibularis longus, fibularis brevis, and fibularis tertius
Pictured here, we can see all three of the fibularis muscles: the fibularis longus, fibularis brevis, and fibularis tertius.

Origin & Insertion

The origin of the fibularis longus is notably expansive, encompassing the head and the superior two-thirds of the lateral surface of the fibula, and extending to the intermuscular septa that separate it from adjacent muscles. This broad origin provides a robust anchorage for the muscle. As it progresses distally, the muscle’s tendon passes posterior to the lateral malleolus and continues past the calcaneus, where it courses underneath the foot, inserting onto the base of the first metatarsal and the medial cuneiform. This distinctive pathway not only facilitates its mechanical leverage but also influences its functional roles in foot movement.[1,2,3]

Fibularis longus origin marked in red
Pictured here, we can see the fibularis longus muscle’s origin highlighted in red on the superior two-thirds of the lateral surface of the fibula.
Fibularis longus insertion marked in blue
Pictured here, we can see the fibularis longus muscle’s insertion highlighted in blue on the base of the first metatarsal and the medial cuneiform.

Action & Function

The fibularis longus plays an important role in foot eversion, where it helps move the foot outward in a lateral direction. This is noticeable when you turn the sole of your foot outward to view it. Additionally, it assists weakly with plantar flexion of the ankle, a movement that involves pointing the toes and foot downward, as seen when standing on your tiptoes.[1,2,3]

Image of a person demonstrating the movement of foot eversion.
This picture demonstrates foot eversion, which means rotating the foot outward, causing the sole of the foot to turn away from the body. The opposite of eversion is inversion. Eversion is the primary action of the fibularis longus.
Image of a person demonstrating the movement of foot plantar flexion.
This image shows an example of foot plantar flexion, which involves extending the ankle. The opposite of plantar flexion is dorsiflexion. Plantar flexion is a secondary action of the fibularis longus.

Innervation

The fibularis longus is innervated by the superficial fibular (superficial peroneal) nerve, with root values of L5 and S1. The superficial fibular nerve is a terminal branch of the common fibular nerve. The common fibular nerve is a branch of the sciatic nerve.[1,2,3]

Superficial fibular nerve (aka peroneal nerve)
Pictured here, we can see the superficial fibular nerve highlighted in red. The superficial fibular nerve innervates the fibularis longus from the nerve roots of L5 and S1. The superficial fibular nerve was previously known as the superficial peroneal nerve.

Blood Supply

Vascularization of the fibularis longus is quite extensive and comes from several arteries. Proximally, its muscular structure receives blood primarily from the anterior tibial artery and the fibular artery (also known as the peroneal artery). It may also receive contributions from the circumflex fibular branch of the posterior tibial artery and the artery accompanying the common fibular nerve (sural communicating artery). Distally, the tendons obtain vascular supply from several sources, including the fibular perforating, anterior lateral malleolar, lateral calcaneal, lateral tarsal, arcuate, and both lateral and medial plantar arteries. However, the two main arteries to remember when considering the blood supply to the fibularis longus, especially in the proximal and middle portions, are the anterior tibial artery and the fibular artery.[2,4,5]

References

  1. [1] Dalley AF II, Agur AMR. Moore’s Clinically Oriented Anatomy. 9th ed. Wolters Kluwer Health; 2022.
  2. [2] Standring S. (2015). Gray’s Anatomy: The Anatomical Basis of Clinical Practice, 41st Edn. Amsterdam: Elsevier
  3. [3] Palastanga N, Soames RW. Anatomy and Human Movement: Structure and Function (Physiotherapy Essentials), 6th ed. Elsevier; 2011. ISBN-13: 978-0702035531.
  4. [4] Lezak B, Varacallo M. Anatomy, Bony Pelvis and Lower Limb: Calf Peroneus Longus Muscle. (Updated 2022 Aug 25). In: StatPearls (Internet). Treasure Island (FL): StatPearls Publishing; 2023 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK546650/
  5. [5] Khan IA, Mahabadi N, D’Abarno A, et al. Anatomy, Bony Pelvis and Lower Limb: Leg Lateral Compartment. (Updated 2023 Aug 14). In: StatPearls (Internet). Treasure Island (FL): StatPearls Publishing; 2023 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK519526/

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