Lateral muscle group (fibular muscles)
The lateral group is represented by the fibular muscles, which perform a number of crucial biomechanical tasks. Their main functions consist of flexion and pronation of the foot. In addition, these muscles are responsible for lowering the medial margin of the foot and play a critical role in supporting its transverse arch.
Innervation of the lateral group is provided by the superficial fibular nerve — n. peroneus superficialis, whose fibers originate from spinal segments L₄–S₁.
Blood supply is provided by branches of the fibular artery (a. peronea), as well as the anterior tibial artery (a. tibialis anterior).
Third fibular muscle
The third fibular muscle (m. peroneus tertius) is an important anatomical structure that in classical anatomy is often regarded not as an independent entity, but as part of the extensor digitorum longus (m. extensor digitorum longus).
- Origin: the muscle originates from the distal (lower) part of the fibula, as well as from the interosseous membrane of the leg.
- Insertion: the muscle tendon securely attaches to the base of the 5th metatarsal bone.
- Functions: unlike the main lateral group, this muscle extends the foot while simultaneously pronating it and raising the lateral margin.
- Innervation: provided by the deep fibular nerve — n. peroneus profundus (segments L₄–S₁).
- Blood supply: supplied by the basins of the fibular and anterior tibial arteries (aa. peronea, tibialis anterior).
Fascial structures and tendon retinacula
Proper functioning of the leg and foot muscles requires secure fixation of their long tendons. This biomechanical role is performed by specialized thickenings of the fascia — retinacula (retinacula).
- Anterior surface of the foot: this is where the superior and inferior extensor retinacula are located — retinacula mm. extensorum superius et inferius. They fix the extensor tendons, preventing their displacement during contraction.
- Lateral surface: the tendons of the fibular muscles are held by the superior and inferior fibular retinacula — retinacula mm. peroneorum superius et inferius.
- Medial surface: this is where the flexor retinaculum is located — retinaculum mm. flexorum, which stabilizes the flexor tendons.
Topographical anatomy and clinical correlations
Knowledge of leg topography is critically important for understanding clinical syndromes and performing physical examinations.
Important anatomical landmarks:
- Leg canal (cruropopliteal canal, canalis cruropopliteus): located between the gastrocnemius muscle (m. gastrocnemius) and the soleus muscle (m. soleus). Passing through this canal are the posterior tibial artery and vein (a. et v. tibialis posterior), as well as the tibial nerve (n. tibialis).
- Nerve branching: in the space between the tibialis posterior (m. tibialis posterior) and the flexor digitorum longus (m. flexor digitorum longus), the tibial nerve divides, giving off branches that form the medial and lateral plantar nerves (n. plantaris medialis et lateralis).
- Pulse points: the pulsation of the popliteal artery (a. poplitea) can be palpated in the popliteal fossa, and the dorsalis pedis artery (a. dorsalis pedis) on the foot.
Clinical correlations:
- «Foot drop»: this characteristic symptom occurs when the deep fibular nerve (n. peroneus profundus) is injured, leading to a loss of extension function.
- Tarsal tunnel syndrome: develops due to compression of the posterior tibial artery (a. tibialis posterior) in the narrow space posterior to the medial malleolus.
- Tendon injuries: the Achilles tendon is the most powerful structure in this region, yet it is susceptible to ruptures. Most commonly, injury occurs during sudden jumps or a strong impact of the heel against a hard surface.
Briefly: answers to topical questions
Which specific muscles make up the lateral muscle group of the leg?
- Fibularis longus (m. peroneus longus) — flexes and pronates the foot, lowers the medial margin, and supports the transverse arch.
- Fibularis brevis (m. peroneus brevis) — flexes and pronates the foot, and raises the lateral margin.
To quickly memorize the location of the tendon retinacula, focus on muscle functions: extensors are always anchored at the anterior aspect of the foot, flexors medially, and fibular muscles strictly laterally.
Class and exam questions
Which leg muscle is frequently described as part of the extensor digitorum longus?
This is the third fibular muscle (m. peroneus tertius). It originates from the distal part of the fibula and the interosseous membrane, and inserts onto the base of the 5th metatarsal bone.
What is the cause of foot drop syndrome?
This pathology occurs upon injury to the deep fibular nerve (n. peroneus profundus), which innervates the muscles responsible for foot extension.
Where is the cruropopliteal canal located and what does it contain?
The cruropopliteal canal (canalis cruropopliteus) is located between the gastrocnemius and soleus muscles. It transmits the posterior tibial vessels (a. et v. tibialis posterior) and the tibial nerve (n. tibialis).
Under what conditions does Achilles tendon rupture most frequently occur?
Despite being the most powerful structure of the leg, its ruptures frequently occur during abrupt jumps or from a heavy impact of the heel on a hard surface.
What else to study on this topic
- The relationship of the third fibular muscle with the extensor digitorum longus (m. extensor digitorum longus).
- Topography and walls of the cruropopliteal canal (canalis cruropopliteus).
- Mechanisms of development of tarsal tunnel syndrome posterior to the medial malleolus.
- Biomechanics of the transverse arch of the foot and the role of the lateral muscle group.
- Branching of the tibial nerve into the plantar nerves (n. plantaris medialis et lateralis).
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