The peroneal (fibular) muscles—fibularis longus and fibularis brevis—form the lateral compartment of the leg and play essential roles in foot eversion, plantarflexion, and ankle stability. Their tendons course behind the lateral malleolus, making them crucial stabilisers of the lateral ankle.
The peroneal muscles consist of fibularis (peroneus) longus and fibularis (peroneus) brevis, both located in the lateral compartment of the leg. They originate along the fibula and insert into bones of the foot, enabling coordinated ankle and foot movement. These muscles are innervated by the superficial fibular nerve (L5–S1) and receive blood supply from branches of the anterior tibial and fibular arteries.
Fibularis (Peroneus) Longus: Anatomy and Tendon Pathway
The fibularis longus originates from the head and proximal two?thirds of the lateral fibula and adjacent intermuscular septum. Its muscle belly descends vertically before forming a narrow tendon in the mid?leg. This tendon passes behind the lateral malleolus, travels through the lateral malleolar groove, and continues along the lateral foot. It then crosses the sole obliquely to insert on the plantar surface of the medial cuneiform and first metatarsal.
Functionally, fibularis longus contributes to plantarflexion, eversion, and support of the longitudinal and transverse arches of the foot. Its tendon becomes prominent when the foot is everted and slightly plantarflexed against resistance.
Fibularis (Peroneus) Brevis: Anatomy and Tendon Pathway
The fibularis brevis lies deep to fibularis longus and originates from the lower two?thirds of the lateral fibular shaft. Its tendon also passes behind the lateral malleolus but differs in its course: it travels superior to the peroneal trochlea, then inserts onto the styloid process of the fifth metatarsal.
Like fibularis longus, fibularis brevis assists in eversion and plantarflexion and plays a key role in stabilising the lateral ankle during dynamic activities such as running on uneven surfaces.
Peroneal Tendons: Structure and Function
The peroneal tendons—extensions of the longus and brevis muscles—run together behind the lateral malleolus within a fibro?osseous tunnel. This region, known as the retromalleolar groove, is a critical anatomical site because the tendons are vulnerable to mechanical stress, subluxation, and injury.
Their combined actions include:
- Eversion of the foot, preventing excessive inversion
- Plantarflexion, assisting propulsion during gait
- Dynamic lateral ankle stabilisation, especially during rapid directional changes
These tendons are particularly important for athletes, as they help maintain balance and prevent ankle sprains.
Clinical Relevance of Peroneal Anatomy
Peroneal tendon disorders are a significant but often under?diagnosed cause of lateral hindfoot pain. Pathologies include:
- Tendinitis and tenosynovitis
- Tendon subluxation or dislocation
- Longitudinal tendon tears
These conditions frequently occur in individuals with chronic ankle instability or cavovarus foot alignment and may result from repetitive athletic activity or inversion injuries.
Accurate diagnosis typically requires clinical examination—palpation of the tendons during resisted dorsiflexion and eversion—and imaging such as ultrasound or MRI.
Functional Integration in Gait and Stability
During walking and running, the peroneal muscles act as lateral stabilisers, counteracting inversion forces and supporting the arches of the foot. Fibularis longus, in particular, helps maintain the transverse arch by pulling the first metatarsal downward and medially. This stabilising action is essential for efficient weight transfer during the stance phase of gait.
The peroneal muscles and their tendons form a biomechanically sophisticated system essential for foot eversion, plantarflexion, and lateral ankle stability. Their anatomical pathways—especially their shared course behind the lateral malleolus—make them both functionally powerful and clinically vulnerable. Understanding their structure and function is crucial for diagnosing and managing lateral ankle disorders, particularly in active individuals.