Fibularis Longus (Peroneus)
Leg · Lower Limb
The fibularis longus (peroneus longus) is the more superficial and longer of the two muscles of the lateral compartment of the leg. It arises from the head and the upper two-thirds of the lateral surface of the fibula, and its long tendon runs behind the lateral malleolus, then crosses obliquely under the sole of the foot to insert on the base of the first metatarsal and the medial cuneiform. This remarkable course lets it evert the foot and assist plantarflexion of the ankle, and because its tendon spans the sole it also supports the transverse and longitudinal arches of the foot. It is supplied by the superficial fibular (peroneal) nerve (L5, S1, S2). Its tendon can be felt behind and below the lateral malleolus during eversion.
Origin, Insertion, Action & Nerve
Origin
Head and upper two-thirds of lateral surface of fibula
Insertion
Base of 1st metatarsal and medial cuneiform (plantar surface)
Action
Eversion of foot; plantarflexion of ankle; supports arches of foot
Nerve
Superficial fibular (peroneal) nerve (L5, S1, S2)
Attachments explained
The Fibularis Longus (Peroneus) is defined first by where it attaches. Its origin is the more fixed anchor, usually the proximal or more stable end that stays put during contraction, while its insertion is the more mobile point that is pulled toward the origin when the muscle shortens.
Origin
Head and upper two-thirds of lateral surface of fibula
Insertion
Base of 1st metatarsal and medial cuneiform (plantar surface)
Action & function
When the Fibularis Longus (Peroneus) contracts, it produces the following movements: Eversion of foot; plantarflexion of ankle; supports arches of foot.
As part of the Leg group of the Lower Limb, it works alongside neighbouring muscles to generate smooth, coordinated movement and to stabilise the structures it acts on.
Nerve supply & clinical relevance
The Fibularis Longus (Peroneus) receives its nerve supply from the Superficial fibular (peroneal) nerve (L5, S1, S2). This nerve carries fibres from spinal segment(s) L5, S1, S2.
Because a muscle can only contract when its nerve is intact, injury to the Superficial fibular or to its spinal roots (L5, S1, S2) can weaken or paralyse the Fibularis Longus (Peroneus), impairing the movements it normally produces (eversion of foot). This is why knowing the innervation is central to localising nerve lesions in clinical practice.
How to study the Fibularis Longus (Peroneus) (the OIANS method)
Fix the fibularis longus by following its unusually long tendon: it descends behind the lateral malleolus, then dives beneath the foot to reach the medial side, ending near where the tibialis anterior inserts. Because it hooks behind the lateral malleolus, it plantarflexes as well as everts, and because it crosses the whole sole, it braces the arches. This crossing tendon is the key image that separates it from every other leg muscle.
Contrast the two everters to lock in the lateral compartment: fibularis longus inserts on the medial side of the foot after crossing the sole, while fibularis brevis inserts on the lateral side at the fifth metatarsal. Both are supplied by the superficial fibular nerve, so a lesion of that nerve significantly weakens eversion and leaves the foot prone to inversion sprains. Linking eversion, plantarflexion, and arch support to that single nerve keeps the picture coherent.
Frequently asked questions
Where is the Fibularis Longus (Peroneus) located?
The Fibularis Longus (Peroneus) is a muscle of the Leg group, located in the Lower Limb.
What is the origin of the Fibularis Longus (Peroneus)?
Head and upper two-thirds of lateral surface of fibula
What is the insertion of the Fibularis Longus (Peroneus)?
Base of 1st metatarsal and medial cuneiform (plantar surface)
What movements does the Fibularis Longus (Peroneus) produce?
Eversion of foot; plantarflexion of ankle; supports arches of foot
What nerve supplies the Fibularis Longus (Peroneus)?
Superficial fibular (peroneal) nerve (L5, S1, S2)
Is the Fibularis Longus (Peroneus) free to study in OIANS?
The Fibularis Longus (Peroneus) is always free to browse. Its full origin, insertion, action and nerve details are open to everyone in the Muscle Directory. Quiz and Flashcard practice for the Lower Limb is part of the one-time Lifetime upgrade, though; only the Upper Limb decks are free to test yourself on.
Related muscles
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