Crural muscles


The foot is moved by a group of muscles known as the crural muscles. The crural muscles are segregated into three basic groups of posterior, anterior, and lateral. The anteromedial aspect of the leg is completely devoid of any attachment sites for muscles.


The tibialis anterior, the peroneus tertius, the extensor hallucis longus, and the extensor digitorum longus are the muscles which make up the anterior crural muscles. Along the lateral segment of the tibia is an excellent site for manual palpation of the tibialis. The oversized superficially placed muscle runs parallel to the obvious crest of the tibia on the anterior portion of the leg.

Laterally positioned to the tibialis is the extensor digitorum longus. Smack between these two muscles is the extensor hallucis longus. Continuous with the extensor hallucis longus runs the much smaller, nearly undersized peroneus tertius muscle.


The Lateral Crural Muscles

The peroneus longus and the peroneus brevis are the two muscles which make up the lateral crural muscles. Laying directly over the fibula one can find the peroneus longus, which is particularly lengthy and flattened. While the peroneus brevis is a much deeper muscle, it is also much closer to the foot. Ankle flexion depends on the complete cohesive unified action of both of these muscles.
Muscles of the Foot
Image: Muscles Of The Foot


There are 7 muscles in the posterior group, which are then subdivided into the superficial group and the deep group. The soleus, the plantaris, and the gastrocnemius muscles belong to the superficial groups while the flexor hallucis longus, the popliteus, the tibialis posterior, and the flexor digitorum longus belong to the deep group.

Most of the part of the leg called the “calf” is created muscularly by the gastrocnemius, the superficial muscle that runs the length of the calf. Its origination point lies in the medial and lateral posterior sections of the epicondyles of the femur. The Achilles tendon, technically referred to as the tendo calcaneus, inserts the muscle into the calcaneus. The gastrocnemius is responsible for flexion of the knee joint as well as plantar flexion of the foot via the ankle.


The Achilles tendon is the strongest tendon in the human body, which of course was made famous in the myth of Achilles. This tendon is not indestructible as it is the most common tendon ruptured during athletic engagement. The deeper laid muscle, the soleus, is also attached to the same insertion point via the Achilles tendon. The soleus muscle and the gastrocnemius muscle, despite the soleus’ much deeper position, are often considered one muscle; the triceps surae. While they share their insertion point, the soleus is only capable of creating plantar flexion of the foot via the ankle joint.


Crural muscles
Image: Crural Muscles

Immediately inferior to the head of the gastrocnemius muscle, the much smaller plantaris muscle begins along the lateral ridge of the femur. Its insertion point is also the calcaneus, but it is attached via a much smaller, more slender tendon. The tendon is so long and thin that many medical students often mistake it for a nerve upon their first dissection assignment. The plataris has some capabilities in providing flexion for the knee and plantar flexion via the ankle, but it is a terribly weak and sometimes almost useless muscle in those with significant injury or other disuse issues.

A section of the popliteal floor, just under the heads of the gastrocnemius muscle, is created by the popliteal muscle. Emerging just under the gastrocnemius heads, it is positioned very deep. The popliteal fossa can be discerned as the depression of the posterior section of the knee joint. The popliteas muscle is designed to assist locomotion efforts via providing necessary, albeit limited, rotation of the knee joint.

Along the posterolateral side of the leg, buried deep in comparison to the soleus muscle, lies the bi-pennate flexor hallucis longus muscle. The joints of the hallus, otherwise known as the great toe, are flexed by the efforts of this muscle. Plantar flexion and foot inversion are also assisted through the efforts of this muscle.


Running parallel to the hallucis longus muscle emerges the deep flexor digitorum longus muscle. It can be found running along the medial portion of the leg. The distal tendon to this muscle is quite vital to numerous regions and is very active, starting its path by the malleolus and continuing along down to the plantar region of the foot. From there, it diverges into four different directions, reaching out to attach to the bone structure of the toes II through V. The flexor digitorum longus thus affect numerous joints. These include flexing of the toes, helping the process of plantar flexing in a small manner, and foot inversion.

In between the posterior flexors and deep when compared to the soleus, the tibialis posterior muscle is responsible for plantar flexion of the foot, arch support of the foot, and foot inversion. It also has a very active distal tendon, which passes the malleolus just posterior and medially, then continues on to insert along the plantar surface of the cuneiform, the navicular, and cuboid bones. From there, it continues on even farther to include the 2nd, 3rd, and 4th metatarsal bones.

The muscular design of the foot is nearly identical to that of the hand. The foot has one additional muscle; the digitorum brevis. Functionally the muscles vary greatly, as the foot is designed to differ in task from the hand. The 4 layers of muscles within the foot are nearly impossible to discern, even during dissection. Muscle contraction in the foot either provides additional support to the arch of the foot or provides flexion and motion for the toes. This assists in both locomotion and structural body support.
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