The peroneal tendons—also known as the fibularis tendons in contemporary anatomical terminology—are a pair of musculotendinous structures that run along the lateral aspect of the leg and ankle. Despite their modest size, they play an outsized role in maintaining ankle stability, controlling foot pronation, and supporting the lateral longitudinal arch of the foot. Because of their exposed course around the lateral malleolus, these tendons are also a common site of injury, particularly among athletes and individuals with chronic ankle instability. Understanding their anatomy provides essential insight into both normal foot biomechanics and the mechanisms behind common pathologies such as tendinopathy, subluxation, and tears.
The Two Peroneal Muscles
The peroneal tendon complex is formed by two muscles: the peroneus longus and the peroneus brevis. Both originate in the lateral compartment of the leg, a fascial compartment bounded by the fibula, the anterior and posterior intermuscular septa, and the crural fascia.
The peroneus longus is the more superficial and proximal of the two. It originates from the head and upper two-thirds of the lateral surface of the fibula, as well as from the intermuscular septa that separate it from the anterior and posterior compartments. Its muscle belly gives way to a tendon that becomes the more posterior and superficial of the two tendons as it descends toward the ankle.
The peroneus brevis lies deep to the longus and originates from the lower two-thirds of the lateral fibula, arising more distally than its counterpart. Its tendon runs anterior to that of the peroneus longus in the distal leg and ankle, a relationship that becomes clinically important in the region behind the lateral malleolus.
Both muscles are innervated by the superficial peroneal nerve (also called the superficial fibular nerve), a branch of the common peroneal nerve, which itself arises from the sciatic nerve. This shared innervation reflects their common developmental and functional origin as evertors of the foot.
Course Behind the Lateral Malleolus
As the two tendons descend, they converge in a shared synovial sheath just proximal to the lateral malleolus. At this level, the peroneus brevis tendon lies anterior and medial to the peroneus longus tendon, and both occupy a shallow groove on the posterior aspect of the distal fibula known as the retromalleolar groove or fibular groove.
The tendons are held in place within this groove by the superior peroneal retinaculum (SPR), a fibrous band that spans from the posterior edge of the fibula to the lateral calcaneus. The SPR is the primary restraint preventing the tendons from subluxating or dislocating anteriorly over the fibula during forceful ankle dorsiflexion and eversion. Deep to the retinaculum, a fibrocartilaginous ridge along the posterior fibula—sometimes reinforced by a low-lying peroneus brevis muscle belly—adds further stability.
Just distal to the tip of the lateral malleolus, the tendons pass through a second fibro-osseous tunnel and separate. The inferior peroneal retinaculum (IPR) then subdivides the shared sheath into two separate compartments over the lateral calcaneus, guided by a bony prominence called the peroneal tubercle (or trochlear process). The peroneus brevis tendon passes superior to this tubercle, while the peroneus longus tendon passes inferior to it, continuing on toward the plantar aspect of the foot.
Distal Insertions
The two tendons diverge significantly in their final destinations, which underlies their distinct biomechanical roles.
The peroneus brevis tendon has the shorter course. It inserts onto the base of the fifth metatarsal, at a small tubercle on its lateral aspect known as the styloid process. This direct, relatively straight path makes the peroneus brevis particularly effective as a strong and consistent evertor of the foot, and its insertion site is also a common location for avulsion fractures during inversion ankle injuries.
The peroneus longus tendon, in contrast, follows a much longer and more circuitous route. After passing inferior to the peroneal tubercle, it curves sharply around the lateral border of the cuboid bone, entering a groove on the plantar surface of the cuboid. Within this groove, the tendon often contains a small sesamoid bone or fibrocartilaginous nodule called the os peroneum, which reduces friction as the tendon changes direction. From here, the tendon crosses the sole of the foot diagonally, passing deep to the long plantar ligament, and inserts onto the plantar-lateral aspect of the base of the first metatarsal and the medial cuneiform. This oblique, plantar course allows the peroneus longus to contribute not only to eversion but also to plantarflexion of the first ray, helping to stabilize the medial column of the foot during the push-off phase of gait.
Vascular Supply and Surrounding Structures
Blood supply to the peroneal tendons comes primarily from branches of the peroneal artery, with additional contributions near the musculotendinous junctions from the anterior tibial artery. A relatively hypovascular “watershed” zone exists just proximal to the tip of the fibula, near the retromalleolar groove—an area thought to be more vulnerable to degenerative tendinopathy due to reduced blood flow combined with mechanical stress from the tight turn the tendons make around the malleolus.
The tendons are closely related to several important structures: the lateral ligaments of the ankle (particularly the calcaneofibular ligament, which lies deep to the peroneal tendon sheath), the sural nerve as it courses posteriorly, and the subtalar joint capsule.
Functional Significance
Functionally, both muscles act as evertors and weak plantarflexors of the ankle, and they play a critical dynamic stabilizing role against excessive inversion, complementing the static restraint provided by the lateral ankle ligaments. The peroneus longus additionally stabilizes the first ray and supports the transverse arch of the foot, which is essential for normal gait mechanics and shock absorption.
The anatomy of the peroneal tendons reflects an elegant balance between mobility and constraint. Their shared origin in the lateral compartment, their passage through a series of retinacular tunnels, and their divergent distal insertions all serve specific biomechanical purposes—chiefly, eversion, ankle stabilization, and support of the foot’s arches. A detailed understanding of this anatomy, including the retinacula, the peroneal tubercle, and the watershed vascular zone, is fundamental to diagnosing and managing the tendinopathies, subluxations, and tears that frequently affect this region.