Module 35: Lower Extremity III – Leg, Ankle, and Foot

Learning Objectives:

By the end of this class, students will be able to:

  • Describe the thigh and leg muscles that act on the knee.
  • Describe the bones and joints of the ankle and foot.
  • Describe the muscles of the leg and foot.
  • Group the muscles of the leg and foot by their location and/or function.
  • Review the anatomy of the lower extremity using clinical application, grouping, and other review methods.

Terms to Know

 

Bones of the Lower Extremity

  • Tibia
    • Anterior tibial border
    • Medial malleolus
  • Fibula
    • Lateral malleolus
  • Tarsals
    • Calcaneus
    • Talus
    • Navicular
    • Cuneiforms
      • Medial
      • Intermediate
      • Lateral
    • Cuboid
  • Metatarsals
  • Phalanges
    • Proximal phalanx
    • Middle phalanx
    • Distal phalanx

Joints of the Lower Extremity

  • Talocrural joint
    • Deltoid ligament
    • Posterior talofibular ligament
    • Anterior talofibular ligament
    • Calcaneofibular ligament
    • Anterior tibiofibular ligament
    • Posterior tibiofibular ligament
  • Intertarsal joints
  • Tarsometatarsal joints
  • Metatarsophalangeal joints
  • Interphalangeal joints
    • Proximal interphalangeal joint
    • Distal interphalangeal joint

Other Lower Extremity Terms

  • Interosseous membrane
  • Plantar fascia
  • Arches of the foot
    • Transverse arch
    • Medial longitudinal arch
    • Lateral longitudinal arch
    • Pes planus*
    • Pes cavus*
 

Muscles of the Lower Extremity

  • Anterior compartment of the leg
    • Extensor digitorum longus
    • Extensor hallucis longus
    • Fibularis (peroneus) tertius
    • Tibialis anterior
  • Lateral compartment of the leg
    • Fibularis (peroneus) longus
    • Fibularis (peroneus) brevis
  • Superficial posterior compartment of the leg
    • Gastrocnemius
    • Soleus
    • Plantaris
  • Deep posterior compartment of the leg
    • Flexor digitorum longus
    • Flexor hallucis longus
    • Tibialis posterior
    • Popliteus
  • Intrinsic muscles of the foot
    • Flexor digitorum brevis
    • Abductor hallucis
    • Abductor digiti minimi
    • Lumbricals
    • Quadratus plantae
    • Adductor hallucis
    • Flexor hallucis brevis
    • Flexor digiti minimi
    • Dorsal interossei
    • Plantar interossei
    • Extensor hallucis brevis
    • Extensor digitorum brevis

 

*Covered only in the lecture videos, not in this text

 

Tibia

This content will be covered in the assignment and briefly reviewed in a lecture video. 

The shaft of the tibia is triangular in shape. Both the anterior tibial border and the medial side of the triangular shaft are located immediately under the skin and can be easily palpated along the entire length of the tibia. The interosseous membrane of the leg is the sheet of dense connective tissue that holds the tibia and fibula bones together.

The large expansion found on the medial side of the distal tibia is the medial malleolus. This forms the large bony bump found on the medial side of the ankle region. Both the smooth surface on the inside of the medial malleolus and the smooth area at the distal end of the tibia articulate with the talus bone of the foot as part of the ankle joint. The lateral side of the distal tibia articulates with the distal end of the fibula, forming the distal tibiofibular joint.

 



Fibula

This content will be covered in the assignment and briefly reviewed in a lecture video. 

The medial border of the thin shaft of the fibula attaches to the interosseous membrane. The distal end of the fibula forms the lateral malleolus, which forms the easily palpated bony bump on the lateral side of the ankle. The medial side of the lateral malleolus articulates with the talus of the foot as part of the ankle joint. The distal fibula also articulates with the tibia.

 


Bones and Joints of the foot

Tarsal Bones

This content will be covered in the assignment and briefly reviewed in a lecture video. 

The posterior half of the foot is formed by seven tarsal bones. The most superior bone is the talus. This has a relatively square-shaped, upper surface that articulates with the tibia and fibula to form the ankle joint. Inferiorly, the talus articulates with the calcaneus, the largest bone of the foot, which forms the heel. Body weight is transferred from the tibia to the talus to the calcaneus, which rests on the ground.

This figure shows the bones of the foot. The left panel shows the superior view, the top right panel shows the medial view, and the bottom right panel shows the lateral view.
Bones of the Foot: The bones of the foot are divided into three groups. The posterior foot is formed by the seven tarsal bones. The mid-foot has the five metatarsal bones. The toes contain the phalanges.

The cuboid articulates with the anterior end of the calcaneus bone. The talus articulates anteriorly with the navicular, which in turn articulates anteriorly with the three cuneiform (“wedge-shaped”) bones. These bones are the medial cuneiform, the intermediate cuneiform, and the lateral cuneiform. Each of these bones has a broad superior surface and a narrow inferior surface, which together produce the transverse (medial-lateral) curvature of the foot. The navicular and lateral cuneiform also articulate with the medial side of the cuboid bone. The joints between the tarsal bones are called the intertarsal joint.

Metatarsal Bones

The anterior half of the foot is formed by the five metatarsal bones, which are located between the tarsal bones of the posterior foot and the phalanges of the toes. These elongated bones are numbered I-V, starting with the medial side of the foot. The first metatarsal bone is shorter and thicker than the others. The second metatarsal is the longest. The base of the metatarsal bone is the proximal end of each metatarsal bone. These articulate with the cuboid or cuneiform bones, forming the tarsometatarsal joints. The base of the fifth metatarsal has a large, lateral expansion that provides a muscle attachment for the fibularis (peroneus) brevis. This expanded base of the fifth metatarsal can be felt as a bony bump at the midpoint along the lateral border of the foot. The expanded distal end of each metatarsal is the head of the metatarsal bone. Each metatarsal bone articulates with the proximal phalanx of a toe to form a metatarsophalangeal joint. The heads of the metatarsal bones also rest on the ground and form the ball (anterior end) of the foot.

Phalanges

The toes contain a total of 14 phalanges (singular phalanx), arranged in a similar manner as the phalanges of the fingers. The toes are numbered 1–5, starting with the big toe, or the hallux. The big toe has two phalanx bones, the proximal and distal phalanges. The remaining toes all have proximal, middle, and distal phalanges. A joint between adjacent phalanx bones is called an interphalangeal joint. The hallux only has an interphalangeal joint, while digits 2-5 have a proximal interphalangeal joint and a distal interphalangeal joint.

 

Arches of the Foot

Fun Fact!

During running, the force applied to each foot as it contacts the ground can be up to 2.5 times your body weight.

This content will be covered in a lecture video. 

When the foot comes into contact with the ground during walking, running, or jumping , the impact of the body weight puts a tremendous amount of pressure and force on the foot. The bones, joints, ligaments, and muscles of the foot absorb this force, thus greatly reducing the amount of shock that is passed superiorly into the lower limb and body. The arches of the foot play an important role in this shock-absorbing ability. When weight is applied to the foot, these arches will flatten somewhat, thus absorbing energy. When the weight is removed, the elastic ligaments maintaining the arches recoil, releasing the stored energy and improving the energy efficiency of walking. Contraction of the foot muscles also plays an important role in this energy absorption. The arches also serve to distribute body weight side to side and to either end of the foot.

The foot has a transverse arch, a medial longitudinal arch, and a lateral longitudinal arch. The transverse arch forms the medial-lateral curvature of the mid-foot. This arch helps to distribute body weight from side to side within the foot, thus allowing the foot to accommodate uneven terrain. The longitudinal arches run down the length of the foot. The lateral longitudinal arch is relatively flat, whereas the medial longitudinal arch is larger (taller).

The principal support for the longitudinal arches of the foot is a deep fascia called plantar aponeurosis, which runs from the calcaneus bone to the toes. The plantar fascia is superficial to the intrinsic muscles of the foot.

 



Ankle Joint

This content will be covered in the assignment and briefly reviewed in a lecture video. 

The ankle is formed by the talocrural joint. It consists of the articulations between the talus bone of the foot and the distal ends of the tibia and fibula of the leg (crural = “leg”). The superior aspect of the talus bone is square-shaped and has three areas of articulation. The top of the talus articulates with the inferior tibia. This is the portion of the ankle joint that carries the body weight between the leg and foot. The sides of the talus are firmly held in position by the articulations with the medial malleolus of the tibia and the lateral malleolus of the fibula, which prevent any side-to-side motion of the talus. The ankle is thus a uniaxial hinge joint that allows only for dorsiflexion and plantar flexion of the foot.

Additional joints between the tarsal bones of the posterior foot allow for the movements of foot inversion and eversion. These motions do not happen at the ankle, but at intertarsal joints of the foot.

The talocrural joint of the ankle is supported by several strong ligaments located on the sides of the joint. On the medial side is the broad deltoid ligament. The deltoid ligament supports the ankle joint and also resists excessive eversion of the foot. The lateral side of the ankle has several smaller ligaments. These include the anterior talofibular ligament and the posterior talofibular ligament, both of which span between the talus bone and the lateral malleolus of the fibula, and the calcaneofibular ligament, located between the calcaneus bone and fibula. These ligaments support the ankle and also resist excess inversion of the foot. The anterior and posterior tibiofibular ligaments hold the distal portions of the tibia and fibula together to support the talocrural joint.

 

This figure shows the structure of the ankle and feet joints. The top panel shows the medial view of the ankle joint, and the bottom panel shows the lateral view.
Ankle Joint: The talocrural (ankle) joint is a uniaxial hinge joint that only allows for dorsiflexion or plantar flexion of the foot. Ligaments that unite the medial or lateral malleolus with the talus and calcaneus bones serve to support the talocrural joint and to resist excess eversion or inversion of the foot.


Muscles of the Leg

This content will be covered in the assignment and reviewed in a lecture video. 

The muscles of the leg are divided into four compartments by thick fascia.

The muscles in the anterior compartment of the leg are the the tibialis anterior, a long and thick muscle on the lateral surface of the tibia, the extensor hallucis longus, deep under it, and the extensor digitorum longus, lateral to it. They all contribute to dorsiflexion. The fibularis tertius, a small muscle that originates on the anterior surface of the fibula, is associated with the extensor digitorum longus and sometimes fused to it, but is not present in all people. Thick bands of connective tissue called the superior extensor retinaculum and inferior extensor retinaculum, hold the tendons of these muscles in place during dorsiflexion.

The lateral compartment of the leg includes two muscles: the fibularis longus (peroneus longus) and the fibularis brevis (peroneus brevis).

The muscles of the superficial posterior compartment of the leg all insert onto the calcaneus, with two of them forming the calcaneal (Achilles) tendon. The most superficial and visible muscle of the calf is the gastrocnemius. Deep to the gastrocnemius is the wide, flat soleus. The plantaris runs obliquely between the two; some people may have two of these muscles, whereas no plantaris is observed in about seven percent of other cadaver dissections.

There are four deep muscles in the posterior compartment of the leg as well: the popliteus, flexor digitorum longus, flexor hallucis longus, and tibialis posterior. The popliteus does not cross the ankle joint. Instead it acts on the knee joint to medially rotate and “unlock” the knee from full extension.

 

The left panel shows the superficial muscles that move the feet and the center panel shows the posterior view of the same muscles. The right panel shows the deep muscles of the right lower leg.
Muscles of the Leg: The muscles of the anterior compartment of the lower leg are generally responsible for dorsiflexion, and the muscles of the posterior compartment of the lower leg are generally responsible for plantar flexion. The lateral and medial muscles in both compartments invert, evert, and rotate the foot.

 

 


Intrisinc Muscles of the Foot

This content will be covered in a lecture video. 

The intrinsic muscles originate and insert within the foot. These muscles primarily provide support for the foot and its arch, and contribute to movements of the toes.

The dorsal group includes two muscles, the extensor digitorum brevis and extensor hallucis brevis (not labeled on the image below).

The plantar group consists of ten muscles in four layers, and these layers can be used to help you organize the muscles as you study. However, we will not ask you to indicate which layer each muscle is located in.

 

This figure shows the muscles of the foot. The top panel shows the lateral view of the dorsal muscles. The bottom left panel shows the superficial muscles of the left sole, the center panel shows the intermediate muscles of the left sole, and the right panel shows the deep muscles of the left sole.
Intrinsic Muscles of the Foot: The muscles along the dorsal side of the foot (a) generally extend the toes while the muscles of the plantar side of the foot (b, c, d) generally flex the toes. The plantar muscles exist in three layers, providing the foot the strength to counterbalance the weight of the body. In this diagram, these three layers are shown from a plantar view beginning with the bottom-most layer just under the plantar skin of the foot (b) and ending with the top-most layer (d) located just inferior to the foot and toe bones.

 

License

Icon for the Creative Commons Attribution 4.0 International License

Anatomy 337 eReader by Rice University is licensed under a Creative Commons Attribution 4.0 International License, except where otherwise noted.

Share This Book