Origin and insertion?
- Origin: originates from the head and upper part of the lateral surface of the fibula, as well as from the leg fascia.
- Insertion: the tendon attaches to the medial cuneiform and first metatarsal bones on the plantar surface.
How does the muscle tendon run?
The tendon passes posterior to the lateral malleolus. The leg fascia is reinforced by two fibular retinacula running to the calcaneus:
- Under the superior retinaculum (retinaculum mm. fibularium superius): the tendon of the fibularis longus passes in a common synovial sheath together with the tendon of the fibularis brevis. The sheath extends 4–5 cm proximal to the ligament.
- Under the inferior retinaculum (retinaculum mm. fibularium inferius): the tendons are located in separate synovial sheaths, divided by the fibular trochlea of the calcaneus (trochlea fibularis).
Further distally, the tendon of the fibularis longus with its synovial sheath passes under the lateral side of the foot, lies in the groove of the cuboid bone, and courses toward the medial side. At the tarsal level, the tendon is enclosed within the fibers of the long plantar ligament (lig. plantare longum), which extends from the calcaneus to the bases of the II–V metatarsal bones.
Topography and adjacent structures
- On the sole, the tendon belongs to the deep, fourth layer of the tarsal region. It is located posterior to the oblique head of the adductor hallucis muscle (caput obliquum m. adductoris hallucis).
- The tendon sheath of m. peroneus longus serves as the site of origin for the opponens digiti minimi muscle (m. opponens digiti minimi).
- In the subcutaneous tissue posterior to the lateral malleolus run the small saphenous vein (v. saphena parva) and the sural nerve (n. suralis).
Functions, blood supply, and innervation
- Function: the muscle performs plantar flexion and pronation of the foot, lowers the medial border, and supports the transverse arch of the foot.
- Blood supply: provided by the anterior tibial artery (a. tibialis anterior) and the fibular artery (a. fibularis/peronea). The latter is a major branch of the posterior tibial artery and runs laterally along the fibula.
- Innervation: superficial fibular nerve — n. peroneus superficialis (roots L₄–S₁).
Clinical significance
- The muscle serves as an indicator for assessing S₁ spinal nerve root lesions. When this root is damaged, the Achilles reflex is also impaired, and the cutaneous sensation zone includes the posterior aspect of the thigh and leg, the lateral edge of the foot, and the sole.
- Evaluation of the muscle strength of the fibularis longus is recommended to objectify motor disorders when assessing weakness of muscles innervated by the tibial nerve.
Class and exam questions
Where does the tendon of the fibularis longus run on the foot?
It runs posterior to the lateral malleolus, passes beneath the lateral side of the foot in the groove of the cuboid bone, and courses toward the medial cuneiform and first metatarsal bones.
In which layer of the sole is the tendon located?
The tendon belongs to the deep, fourth layer of the tarsal region, lying posterior to the oblique head of the adductor hallucis muscle.
Damage to which nerve root can be suspected in case of weakness of this muscle?
The fibularis longus muscle acts as an indicator for the S₁ spinal root.
What else to study on this topic
- Fibularis brevis muscle (m. peroneus brevis)
- Superficial fibular nerve (n. peroneus superficialis)
- Fibular retinacula
- Topography of the deep layer of the sole
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