Muscles of the Lower Leg and Foot

By OpenStax [CC BY 4.0 (http://creativecommons.org/licenses/by/4.0)], via Wikimedia Commons

Lower Leg Muscles

The muscles of the lower leg reside in four facial compartments. A fascia surrounding each compartment serves to contain the compartment muscles and separate them other nearly structures.

The lower leg has four facial compartments. These are the anterior compartment, lateral compartment, deep posterior compartment and superficial posterior compartment. Each compartment contains muscles generally dedicated to a limited set of movements.

You will again find it useful to review the article on Anatomical Terminology while exploring the material presented below.

Anterior Compartment Muscles

The muscles in the anterior compartment produce or help with dorsiflexion, inversion, and eversion of the foot. The muscles in this compartment are the tibialis anterior, extensor digitorum longus, extensor hallucis longus, and fibularis tertius. The anterior compartments are anterior to, and between, the tibia and fibula.

The tibialis anterior is a fusiform muscle that originates on the tibia beginning at the lateral condyle and extending inferiorly for a little over half the length of the lateral side of the tibia shaft. The muscle has a long tendon that crosses the anterior medial ankle and extends into the foot where it inserts into the first (medial) cuneiform bone and then the first metatarsal bone. The tibialis anterior performs two essential functions. The first is dorsiflexion and the second is foot inversion.

Tendons of the foot by Henry Vandyke Carter [Public domain], via Wikimedia Commons

Sitting lateral and posterior to the tibialis anterior is the extensor digitorum longus muscle. The extensor digitorum longus originates from the lateral condyle of the tibia, the anterior surface along the top three-quarters of the fibula, and from various nearby connective tissues. It descends through the ankle and then along the dorsum of the foot. It then inserts via four separate tendons (clearly visible in the lateral view of the foot at right) to the first and second phalanges of each of four smaller toes. The muscle provides dorsiflexion and eversion of the foot and extension of the toes.

The Latin word hallucis means ‘related to the big toe.’  Therefore, the extensor hallucis longus muscle functions to extend the big toe. It also contributes to dorsiflexion of the foot. It originates along the lower medial side of the fibula between the tibialis anterior and extensor digitorum longus. It crosses the ankle and a long tendon inserts into the distal phalanx of the big toe.

The fibularis tertius (also called the peroneus tertius) is a relatively small muscle originating along the lower third of the anterior surface of the fibula. It crosses the ankle on the dorsal side of the foot and inserts via a tendon onto the dorsal side of the metatarsal for the little toe. It provides weak support for dorsiflexion of the foot and also provides eversion of the foot.

Lateral Compartment Muscles

The lateral compartment is found on the lateral side of the fibula. Muscles found in the lateral compartment are the fibularis longus and fibularis brevis. These muscles are also called the peroneus longus and peroneus brevis, respectively. These two muscles aid in plantar flexion and eversion of the foot. Both actions help stabilize the leg over the foot and are instrumental in helping you maintain balance when walking or standing.

The fibularis longus originates at the lateral condyle of the tibia and along the upper two-thirds of the lateral side of the fibula. A long tendon then runs behind the lateral ankle bone ( lateral malleolus) and then obliquely across the bottom of the foot (across the arch of the foot) before inserting at the base of the first metatarsal bone and the lateral side of the medial cuneiform. The muscle supports eversion and plantar flexion the foot. These actions help steady the leg above the foot such as you experience when standing in Ippon Dachi.  Because the tendon crosses the bottom of the foot it is also instrumental in maintaining and supporting the transverse arch of the foot.

The fibularis brevis originates along the lateral lower two-thirds of the fibula. Like the fibularis longus, the fibularis brevis has a long tendon that passes behind (posterior to) the lateral malleolus. This tendon runs forward along the bottom of the foot, eventually inserting into the base of the fifth metatarsal.  The muscle participates in eversion and plantar flexion of the foot.

Deep Posterior Compartment Muscles

The deep posterior compartment resides immediately posterior to both the tibia and fibula. This compartment is deep to the superficial posterior compartment (discussed later) and includes the popliteus ,flexor hallucis longus, flexor digitorum longus, and tibialis posterior, muscles.

The popliteus muscle originates on the lateral surface of the lateral condyle of the femur. It then wraps posteriorly behind the knee as it descends obliquely, ultimately inserting on the posterior surface of the tibia. The muscle flexes the leg at the knee and unlocks the knee-joint when walking. It performs the latter action by laterally rotating the femur about the tibia, allowing a straightened knee to begin flexion.

The flexor hallucis longus muscle originates along the distal two-thirds of the posterior aspect of the fibula. It then descends via a long tendon that runs behind the medial side of the ankle (posterior to the medial malleolus). The tendon then extends along the bottom of the foot and inserts into the base of the distal phalanx of the big toe (hallux). The muscle causes flexure of the big toe, but also assists in plantar flexion and inversion of the foot. In addition, it assists with supination of the ankle.

Flexion of the other four toes of the foot emanates from actions of the flexor digitorum longus muscle. This muscle originates along most of the posterior surface of the tibia. A long tendon passes posteriorly to the medial malleolus and then moves medially as it crosses the sole of the foot. It divides into four tendons that insert into the distal phalanx of the second through the fifth toe. The muscle functions to flex these toes but also aids in plantar flexion and inversion of the foot.

Emerging from the medial posterior borders of both the tibia and fibula is the tibialis posterior muscle. Like the flexor digitorum longus, the tendon of the tibial posterior muscle descend posteriorly around the medial malleolus. The thick tendon divides into three sections. The plantar section inserts into the bases of the second, third, and fourth metatarsals and the cuboid bone. The recurrent section inserts into the sustentaculum tali on the superior portion of the calcaneus (heel bone). The main section of the tendon inserts into the medial (first) cuneiform bone proximal to the big toe. The muscle helps stabilize the leg over the foot and assists with plantar flexion and inversion of the foot.It also provides stabilization of the medial arch of the foot. This is the most powerful of the muscles in the deep posterior compartment. 

Superficial Posterior Compartment Muscles

This compartment contains the gastrocnemius, soleus, and plantaris muscles. These muscles provide plantar flexion. As the compartment name suggests, these muscles are found posterior to the tibia and fibula and superficial to those muscles found in the deep posterior compartment.

The gastrocnemius muscle originates from both the lateral and medial condyle of the femur. The resulting two muscle bundles descend along the posterior of the leg. The soleus muscle originates just below the knee and lies deep to the gastrocnemius muscles. Both the soleus and the gastrocnemius muscles eventually join to form the large single Achilles Tendon (Tendo calcaneus). The Achilles Tendon is the thickest tendon in the human body and inserts into the posterior surface of the calcaneus. The gastrocnemius and soleus muscles jointly comprise the calf muscle (some anatomists consider these a single muscle). They are responsible for plantar flexion and flexing of the knee-joint.

The plantaris muscle originates on the femur just superior to the lateral head of the gastrocnemius muscle. The plantaris has a relatively short body but a very long tendon (the longest tendon in the human body). The tendon eventually merges near the distal end of the Achilles Tendon.

Intrinsic Foot Muscles

By OpenStax [CC BY 4.0 (https://creativecommons.org/licenses/by/4.0)], via Wikimedia Commons

Muscles found in the lower leg that affect movements of the foot are extrinsic muscles. They are muscles that do not actually reside within the foot itself. Intrinsic foot muscle are those muscles that are found in the foot. The muscles fit into two categories: dorsal muscles and plantar muscles.

Dorsal Foot Muscles

Dorsal foot muscles are found on the dorsal or top portion of the foot. There are only two muscles in this section, the extensor digitorum brevis and the extensor hallucis brevis.

Extension of the toes receives help from the extensor digitorum brevis and extensor hallucis brevis muscles. Anatomists often classify these as a single muscle; the extensor digitorum brevis muscle. It originates along the anterior and lateral surfaces of the calcaneus and extends toward the toes. It also originates from the interosseous talocalcaneal ligament and the stem of the inferior extensor retinaculum, the Y-shaped ligament that wraps over the top of the foot just below the ankle. The muscle ends in four tendons. The medial tendon (which some anatomists consider part of the separate extensor hallucis brevis muscle) inserts along the dorsal surface of the proximal phalanx of the big toe. The remaining three tendons insert into the lateral side of tendons from the extensor digitorum longus muscle for the second through fourth toe.

Plantar Foot Muscles

Muscles in the plantar foot are found in four distinct layers, each layer deeper than the previous layer. We will begin by exploring the most superficial layer first and then discuss each deeper layer in turn. Keep in mind that the most superficial layer is closest to the bottom (plantar side) of the foot.

Superficial Layer

The muscles in the superficial layer are the abductor hallucis, flexor digitorum brevis, and abductor digiti minimi.

The abductor hallucis provides abduction of the big toe. It originates at the medial tubercle of the calcaneus, the flexor retinaculum, and nearby connective tissues (the plantar aponeurosis). It inserts on the medial side of the proximal phalanx of the big toe. The muscle provides abduction and assists with flexion of the big toe.

The flexor digitorum brevis has similar points of origin to the abductor hallucis. It inserts via four tendons to the intermediate phalanges of the four lesser toes. The muscle causes flexure of the four smaller toes at the proximal interphalangeal joints.

The abductor digiti minimi muscle provides abduction of the little toe. This muscle originates along the medial and plantar surfaces of the calcaneus. It inserts on the lateral side of the proximal phalanx of the little toe. In addition to its abduction function the muscle also aids flexion of the little toe.

Intermediate Layer

Deep to the superficial layer is the intermediate set of muscles composed of the quadratus plantae and the lubricals.

The quadratus plantae originates on both the medial and lateral plantar surfaces of the calcaneus. It inserts into the tendons of the flexor digitorum longus muscle, thereby aiding these muscles with flexion of the four smaller toes.

The lubricals consist of four muscles that originate from the tendons of the flexor digitorum longus muscle. Each of the four muscles resides medially to the tendon from which it originates. The muscles insert at the extensor hood of the four smaller digits. Each muscle functions to flex its associated metatarsophalangeal joint while extending its associated interphalangeal joint.

Deep Layer

The deep layer contains three muscles. These are the flexor hallucis brevis, abductor hallucis, and flexor digiti minimi brevis.

The flexor hallucis brevis originates on the plantar side of the cuboid and lateral cuneiform bones. It inserts at the base of the proximal phalanx of the big toe. The muscle serves to flex the metatarsophalangeal joint of the big toe.

The abductor hallucis has two heads called the oblique and lateral heads. The oblique head originates at the second through fourth metatarsal bones. The lateral head originates from the plantar ligaments of the metatarsophalangeal joint of each of the four smaller toes.Both heads attach at the lateral base of the proximal phalanx of the big toe. The muscle functions to abduct the big toe and assists with formation of the transverse arch of the foot.

Flexion of the little toe receives help from action of the flexor digiti minimi brevis muscle. This muscle originates at the base of the fifth metatarsal and inserts at the base of the proximal phalanx of the little toe.

Deepest Layer

The deepest layer consists of muscles found between the metatarsal bones. The muscles here are the plantar interossei and dorsal interossei. These muscles are similar to the palmar interossei and dorsal interossei of the hand.

The dorsal interossei of the foot are bipennate muscles that arise from the dorsal edges of two adjacent metatarsal bones. One muscle inserts on both the medial and lateral sides of the proximal phalanx of the second digit. The remaining two muscles insert on the lateral side of proximal phalanx of the third and fourth digit. Whereas these muscles function to provide limited abduction of digits two through four and cause flexion of the metatarsophalangeal joint on these digits.

The plantar interossei are unipennate muscles that arise from the plantar edge of a metatarsals three through five. Each muscle inserts on the medial side of the proximal phalanx of the same digit. These muscles function to offer limited adduction of digits three through five and provide flexure of the metatarsophalangeal joint of these same digits.

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