Lower Leg Flashcards
Describe the muscles within the anterior compartment of the leg.
There are four muscles in the anterior compartment of the leg; tibialis anterior, extensor digitorum longus, extensor hallucis longus and fibularis tertius.
Collectively, they act to dorsiflex and invert the foot at the ankle joint. The extensor digitorum longus and extensor hallucis longus also extend the toes. The muscles in this compartment are innervated by the deep fibular nerve (L4-L5), and blood is supplied via the anterior tibial artery.
Tibialis anterior
The tibialis anterior muscle is located alongside the lateral surface of the tibia. It is the strongest dorsiflexor of the foot.
Attachments: Originates from the lateral surface of the tibia, attaches to the medial cuneiform and the base of metatarsal I.
Actions: Dorsiflexion and inversion of the foot.
Innervation: Deep fibular nerve.
Extensor digitorum longus
The extensor digitorum longus lies lateral and deep to the tibialis anterior. The tendons of the EDL can be palpated on the dorsal surface of the foot.
Attachments: Originates from the lateral condyle of the tibia and the medial surface of the fibula. The fibres converge into a tendon, which travels to the dorsal surface of the foot. The tendon splits into four, each inserting onto a toe.
Actions: Extension of the lateral four toes, and dorsiflexion of the foot.
Innervation: Deep fibular nerve.
Extensor hallucis longus
The extensor hallucis longus is located deep to the EDL and TA.
Attachments: Originates from the medial surface of the fibular shaft. The tendon crosses anterior to the ankle joint and attaches to the base of the distal phalanx of the great toe.
Action: Extension of the great toe and dorsiflexion of the foot.
Innervation: Deep fibular nerve.
Fibularis tertius muscle
The fibularis tertius muscles arises from the most inferior part of the EDL. It is not present in all individuals, and is considered by some texts as a part of the extensor digitorum longus.
Attachments: Originates with the extensor digitorum longus from the medial surface of the fibula. The tendon descends with the EDL, until they reach the dorsal surface of the foot. The fibularis tertius tendon then diverges and attaches to metatarsal V.
Actions: Eversion and dorsiflexion of the foot.
Innervation: Deep fibular nerve.
What is foot drop?
Footdrop is a clinical sign indicating paralysis of the muscles in the anterior compartment of the leg. It is most commonly seen when the common fibular nerve (from which the deep fibular nerve arises) is damaged.
In footdrop, the muscles in the anterior compartment are paralysed. The unopposed pull of the plantarflexor muscles (found in the posterior leg) produces permanent plantarflexion. This can interfere with walking – as the affected limb can drag along the ground. To circumvent this, the patient can flick the foot outwards while walking – known as an ‘eversion flick‘.
Describe the action of the muscles within the inferior posterior leg
The posterior leg is the largest of the three compartments. Collectively, the muscles in this area plantarflex and invert the foot. They are innervated by the tibial nerve, a terminal branch of the sciatic nerve.
Describe the superficial muscles of the posterior leg
The superficial muscles form the characteristic ‘calf’ shape of the posterior leg. They all insert into the calcaneus of the foot (the heel bone), via the calcaneal tendon.
Gastrocnemius
The gastrocnemius is the most superficial of all the muscles in the posterior leg. It has two heads – medial and lateral, which converge to form a single muscle belly.
Attachments: The lateral head originates from the lateral femoral condyle, and medial from the medial condyle. The fibres converge, and form a single muscle belly. In the lower part of the leg, the muscle belly combines with the soleus to from the calcaneal tendon, with inserts onto the calcaneus (the heel bone).
Actions: It plantarflexes at the ankle joint, and because it crosses the knee, it is a flexor there.
Innervation: Tibial nerve.
Plantaris
The plantaris is a small muscle with a long tendon, which can be mistaken for a nerve as it descends down the leg. It is absent in 10% of people.
Attachments: Originates from the lateral supracondylar line of the femur. The muscle descends medially, condensing into a tendon that runs down the leg, between the gastrocnemius and soleus. The tendon blends with the calcaneal tendon.
Actions: It plantarflexes at the ankle joint, and because it crosses the knee, it is a flexor there. It is not a vital muscle for these movements.
Innervation: Tibial nerve.
Soles
The soleus is located deep to the gastrocnemius. It is large and flat, named soleus due to its resemblance of a sole – a flat fish.
Attachments: Originates from the soleal line of the tibia and proximal fibular area. The muscle narrows in the lower part of the leg, and joins the calcaneal tendon.
Actions: Plantarflexes the foot at the ankle joint.
Innervation: Tibial Nerve.
Describe the actions of the muscles in the deep compartment of the inferior posterior leg.
There are four muscles in the deep compartment of the posterior leg. One muscle, the popliteus, acts only on the knee joint. The remaining three muscles (tibialis posterior, flexor hallucis longus and flexor digitorum longus) act on the ankle and foot.
Popliteus
The popliteus is located superiorly in the leg. It lies behind the knee joint, forming the base of the popliteal fossa.
There is a bursa (fluid filled sac) that lies between the popliteal tendon and the posterior surface of the knee joint. It is called the popliteus bursa.
Attachments: Originates from the posterior surface of the proximal tibia. The fibres pass upwards and laterally, attaching to the lateral condyle of the femur and the lateral meniscus of the knee joint.
Actions: Laterally rotates the femur on the tibia – ‘unlocking’ the knee joint so that flexion can occur.
Innervation: Tibial nerve.
Tibialis posterior
The tibialis posterior is the deepest out of the four muscles. It lies between the flexor digitorum longus and the flexor hallucis longus.
Attachments: Originates from the interosseous membrane between the tibia and fibula, and posterior surfaces of the two bones. The tendon enters the foot posterior to the medial malleolus, and attaches to the plantar surfaces of the medial tarsal bones.
Actions: Inverts and plantarflexes the foot, maintains the medial arch of the foot.
Innervation: Tibial nerve.
Flexor digitorum longus
Flexor Digitorum Longus
The FDL is (surprisingly) a smaller muscle than the flexor hallucis longus. It is located medially in the posterior leg.
Attachments: Originates from the medial surface of the tibia, attaches to the plantar surfaces of the lateral four digits.
Actions: Flexes the lateral four toes.
Innervation: Tibial nerve.
