The Foot And Ankle

Bony Structures of the Lower Leg, Ankle and Foot

The foot contains 26 bones, 31 joints, and 20 intrinsic muscles (small muscles in the foot). 

 
The foot and ankle are generally discussed by breaking them into several anatomical regions. The ankle joint, which is the distal aspect of the tibia and the fibula articulating with the talus, is the most proximal joint. The foot is divided into the rearfoot, the midfoot and the forefoot structures.

Distal Tibia and Fibula

The proximal ends of the tibia and fibula were discussed in Unit VII. The distal ends of these two bones form the cornerstones of the ankle joint. The distal tibia has a medial malleolus that forms the interior bump you feel on the inner surface of the ankle. The distal fibula has a longer more pointed bony structure called the lateral malleolus and is the bump you can feel on the exterior surface of the ankle. Both of these bones have articular surfaces that articulate with the talus to form the mortise joint of the ankle.  When these two bones are in anatomical alignment they form a mostly square joint space at their distal aspects. The body of the talus fits nicely into this joint space. (Note the square space at the distal end of the bones in the picture to the left. It is the space between the medial and lateral malleoli)
The Talus and Calcaneus  (Part of the Rearfoot Structures)

The talus and the calcaneus are the two most posterior bones in the foot, as well, as the largest of the tarsal bones of the foot. The talus articulates with the distal tibia and fibula above to form the mortise joint of the ankle. It articulates below with the calcaneus. No muscles actually insert on the talus. The talus is moved indirectly by muscles acting around it.  (In the picture to the left the talus is the bone on the top, and the calcaneus is the larger bone below it)
  The superior aspect of the talus is called the body. It has three articulating surfaces for articulation with the tibia and fibula above. The head of the talus is located more inferiorly and anteriorly and serves to articulates with the navicular bones of the mid-foot and inferiorly to the calcaneus below. The narrowed section between the body and the head is called the neck of the talus. On the medially surface of the talus are two tubercles with a groove between them. This groove is for the passage of the flexor hallucis longus tendon.

The calcaneus is a large, irregularly-shaped bone.  It is a longer bone that comprises the rearmost portion of the foot that strikes the ground at the heel.
 The posterior aspect of the calcaneus has a tuberosity for contact with the ground at the heel. Near the middle of the bone, on its superior aspect, is the articulation site with the talus above. The anterior projection of the calcaneus has an articulation also with the talus, as well as with the cuboid bone of the mid-foot. There is a prominent projection on the medial portion of the calcaneus called the sustentaculum tali. This projection has an accompanying groove through which tendons, and vessels attach. On the posterior aspect of the calcaneus is an insertion area for the large achilles tendon.
The Midfoot Bony Structures

Anterior to the rearfoot complex of the calcaneus and talus is the midfoot. It lies between the rearfoot, and the forefoot structures. If you view the foot from the medial aspect and see the area commonly called the “instep” this would correspond with the location of the midfoot structures. There are five bones that make up the midfoot: 
  • the cuboid,
  • the navicular,  
  • the 3 cuneiforms. 

The navicular articulates with the talus of the rearfoot on its proximal end. The distal end of the navicular articulates with the 3 cuneiform bones. It has a medial tubercle that can be felt externally on the foot. This tubercle is for the insertion of the tibialis posterior muscle. 

The cuboid articulates proximally with the calcaneus of the rearfoot. It also articulates with the navicular bone medially, and with the 3rd cuneiform bone. It articulates with the metatarsals distally (forefoot structures). A lateral bony notch is present that serves to hold the tendon of the peroneus longus muscle. 

The cuneiform bones are three small, edge-shaped bones with sharp edges. They articulate with navicular proximally and with the metatarsals distally. The mid-foot joints allow some degree of flexibility in the foot.

(Notice in the picture to the left the middle section, or midfoot, and how the bony structures fit together. Note also which midfoot bones touch bones in the other sections of the foot).

 
The Forefoot Bony Structures

The most distal aspect of the foot comprises the forefoot. It consists of two types of bony structures:
  •  the metatarsals 
  •  the phalanges 

These bones are much like the bones of the distal hand, except the big toe, unlike the thumb, is not opposable. 

Each metatarsal consists of a proximal base, a body, and a distal head. (See picture top left) The base is mostly a square shape and has facets that articulate with the tarsals of the mid-foot, as well as with adjacent metatarsals. The head is round with a cartilaginous surface for articulation with the proximal phalanx. The body is triangular like most long bones.

Each toe has a proximal, middle, and distal phalanx as seem at left. The proximal phalanx is the longest. Collectively they are called phalanges.

These all articulate with each other to form the bony structure of the toes.
 

 
Lay-Out of the Bones of the Foot 

When all of the bones of the foot are viewed together there are some important anatomical combinations that are important functional units for the foot.

Viewed from the medial side of the foot you can see the longitudinal arch of the foot. It runs front to back and forms the natural visible arch with the floor or ground below.

The bones of the rearfoot, especially the calcaneus forms the floor contact for the rear of the arch. The metatarsal heads form the front contact point with the ground.

The foot is also generally divided into the lateral foot and the medial foot by joint articulations. 

The lateral foot consists of:

  • the calcaneus, 
  • the cuboid, 
  • and the metatarsals and phalanges of toes 4 and 5. 

  It includes the lateral arch of the foot and is more involved in weight bearing activities during walking and running.

 The medial foot consists of :

  • the talus,
  • the navicular, 
  • the cuneiforms, 
  • and the metatarsal and phalanges of toes 1, 2, and 3.

The medical foot includes the medial arch and is more involved in propulsion (moving the body through space during walking).

The bones of the midfoot form the arch of the foot. Viewed from above the foot also has a transverse arch that runs medial to lateral across the foot. The first and fifth metatarsals are the contact points with the ground for this arch. The bones of the mid-foot and the metatarsals form the elevated- point for this arch.  

Viewed from above the foot appears to consist of 5 spokes (the metatarsals and toes) that splay out from the tarsals behind them.
In the picture to the right you can see a schematic illustrating the support system of the longitudinal and transverse arches of the foor.

Joints of the Foot and Ankle

 
The joints in the foot and ankle are many and complex. In this course you will be provided basic information about how these joints move, but the actual biomechanics of the joints are quite complex, especially the sub-talar joint.

 
The Ankle Joint

The ankle joint is comprised of the distal aspects of the tibia and fibula that form a square shaped opening in which the body of the talus fits. There are three articulations on the surface of the talus for articulation with the tibia and fibula. Recall from the discussion above that the body of the talus is dome shaped or rounded so that this rounded surface fits into the opening above it. It is a snug fit for this joint. 

The lateral malleolus extends down more distally along the lateral surface of the talus. Because of this tight fit this joint is a pure hinge joint – it only has available motion in one plane. 
The ankle joint only moves in dorsiflexion and plantarflexion. It does have a great deal of motion in both directions, more than any other joints in the foot or ankle. When the foot moves into dorsiflexion the body of the talus moves further into the joint space and makes the foot tighter and more stable. When the foot moves into plantarflexion the more narrow portion of the talus is in contact with the bones above and thus the joint is less stable

The Subtalar Joint 

Below the ankle joint is the subtalar joint comprised of the articulations between the talus and the calcaneus bones. There are two articulating surfaces on each bone that form the joint. One surface is concave and the other convex on each bone. In other words there is a dip and a bump on each bone that fit into one another to form the joint. 
The calcaneus and the talus are not lined up equally and fit together so that the talus is oriented more medially and the calcaneus more laterally.  Because this joint is biomechanically angular in its orientation is has multiple planes in which movement occurs. The subtalar joint produces plantarflexion and dorsiflexion, as well as abduction and adduction of the foot. These two planar motions when combined form the components of inversion and eversion of the ankle which will be discussed more fully below.

 
The Transverse or Mid Tarsal Joints

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Moving distally along the ankle and foot, the next joints are the transverse or mid tarsal joints. These are the joints between the rear foot and the midfoot structures. There are two joints
  • the talonavicular 
  • the calcaneocuboid.

 The talus articulates with the navicular bone to form the more medial talonavicular joint.The calcaneus articulates with the cuboid to form the more lateral calcaneocuboid joint. 

  Viewed from above these joints are more of a curved shape across the middle of the foot, rather than a straight line. Because of this shape is provides motion of inversion and eversion of the foot. The transverse tarsal joints have a key role in adjusting the foot when walking on uneven surfaces.

 

The Cuneiform Joints  

The cuneiform bones articulate with the cuboid, the navicular, and each other to make up the other portion of the midfoot joints. They also participate in the inversion and eversion action at the midfoot. 
 

The Tarsometatarsal Joints  

Further distally into the foot are the joint structures that split the midfoot from the forefoot. The three cuneiform bones of the midfoot and the cuboid articulate with the bases of the five metatarsal bones to form the tarsometatarsal joints. 

The joint line across the foot is irregular and does not form a straight line. Metatarsal 1 articulates with the medial cuneiform. Metatarsal 2 fits into a notch formed by the three cuneiforms. Metatarsal 3 articulates with the most lateral cuneiform and Metatarsals 4 and 5 fit against the cuboid bone. The available motions at these joints are plantarflexion and dorsiflexion of the midfoot. 
 

The Metatarsalphalangeal(MP) and Interphalangeal(IP) Joints

The MP and IP joints are the articulations of the heads of the metatarsals with the proximal phalanges and the articulations of the proximal phalanges to the middle phalanges, and the middle phalanges to the distal phalanges. These are commonly referred to as the toe joints of the foot.  Toes 2-5 have three joints, and the great toe has only two since there is no middle phalanx in the great toe. The great toe phalanges are much larger than the phalanges bones of the other toes. It plays an important role in walking when the toes are in contact with the ground.  

The metatarsalphalangeal joints allow three types of movement: 

  • dorsiflexion and plantar flexion of the toes 
  • abduction and adduction of the toes
  • slight medial lateral rotation.

 The interphalangeal joints are hinge joints that allow only plantarflexion and dorsiflexion of the toes.

 Plantarflexion of the toes has more range of motion in the foot than Dorsiflexion. This allows the individual to stand on tiptoe.
So a quick recap of the joints:
  •  the ankle joint is most proximal
  •  the subtalar joint below it 
  •  the two midtarsal joints
  •  the tarsometatarsal joints with the tarsals and the metatarsals of each toe
  •  the metatarsal joints with the proximal phalanges, 
  •  the joints of the phalanges that make up the distal toes.

 The ankle is a complex set of joints. Understanding the ligamentous support is also important

 
Ligaments of the Foot and Ankle
There are many small ligaments that connect the various bones of the foot and ankle. There is also a larger ligamentous structure on the bottom of the foot. These ligaments provide additional stability to the foot and ankle.
The Talofibular and Calcaneofibular Ligaments

Thetalofibular and calcaneofibular ligaments are probably the best known ligaments in the body. This is the set of ligaments injured when someone rolls over on the outside of the foot and sprains the ankle. The talofibular ligaments are actually two small ligaments that run from the distal end of the lateral malleolus of the fibula to the talus below. The calcaneofibular ligament is a small ligament that runs from the distal malleolus of the fibula to the calcaneus below. Together they form a 3 pronged structure on the lateral (outside) aspect of the ankle.

 These small ligaments can be easily damaged or torn with spraining of the ankle. They help provide lateral static stability to the ankle.
 

The Deltoid Ligament 

On the medial aspect of the ankle is the deltoid ligament. It runs from the medial malleolus of the tibia to the talus, and the navicular bone. It is a broad, fan shaped ligament with two smaller ligaments beneath it that provide a great deal of stability to the medial side of the ankle. It is very unusual for someone to roll the ankle to the inside and damage this ligament, rather a fracture of one of the bones would more likely occur first.
 

Other Smaller Ligaments in the Rearfoot and the Midfoot
There are several smaller ligaments that attach between the calcaneus, the tibia, and the midtarsal bones. It is beyond the scope of this course to discuss each ligament. It is important to remember, however, that the presence of this network of ligaments between the bones of the foot provide additional stability the foot requires for constant stresses of weightbearing.
The Plantar Ligament
The largest ligamentous structure in the foot is the plantar ligament. It is also commonly called the plantar fascia. If you have heard someone say that have plantar fascitis it is an inflammatory condition in this ligament. The plantar ligament is on the bottom of the foot (the plantar surface) and runs from the calcaneus to attach to the bases of metatarsals II-V. It is quite a strong ligament and helps support the arches of the foot. When seen on cadavers it appears thick and striated, much like reinforced packing tape might be on a cardboard box. It is impossible to tear that packing tape, it must be cut. The plantar fascia is dense and strong to support the foot.
 

Metatarsalphalangeal and Interphalangeal Ligaments
There are small ligaments in the toes that have the same general arrangement. Each joint has two collateral ligaments on each side of the joint.  There is a glenoid ligament on the bottom of the toe that runs across the joint, and there is the deltoid or fanned shaped ligament that runs from the proximal joint to the glenoid ligament border. These ligaments provide stability at each of the small joints of the toe.
 The bones of the foot and ankle are many, but fit snugly together for overall stability. The addition of several small ligaments attaching bone-to-bone provides further stability. The large plantar ligament provides a great deal of stability to the arch and bottom of the foot. The final overlay of muscles then provides both dynamic and static stability to the foot and ankle. The foot and ankle bear the brunt of the weight of the body above it, as well as taking on the ground forces beneath it. This will be discussed more fully later.

 
Motions of the Foot and Ankle

Dorsiflexion – This motion is the pulling up of the foot. The toes are moving closer to the front of the lower leg. The angle between the superior surface of the foot and the anterior leg is getting smaller. In lay language most people will say they “flex” the foot to achieve this position.  Dorsiflexion is greater when the knee is flexed and less when the knee is extended. This is because in knee extension there is greater tension on the gastrocnemius muscles (the large muscle in the back of the lower leg). 

Plantarflexion – This motion is moving the toes away from the front of the leg, or increasing the angle between the superior surface of the foot and the anterior leg. It is often referred to as extending the foot, or in dance terms would be pointing the foot or toes.
Dorsiflexion and Plantarflexion occur primarily at the ankle joint. You can also dorsiflex or plantar flex the toes of the forefoot separate from the rearfoot structures of the ankle.
Abduction – This is moving the distal end of the foot away from midline, or away from the center of the body. This motion occurs primarily at the subtalar and more distal joints.

Adduction – This is moving the distal end of the foot toward the midline, or toward the center of the body.   This motion occurs primarily at the subtalar and more distal joints.
Inversion – This is the combination movement of adduction and plantar flexion at the ankle complex. When you perform this motion the sole of the foot is directed toward the midline of the body with the great toe pointing down slightly.
  • Inversion = adduction + plantarflexion

Eversion – This is the combination movement of abduction and dorsiflexion at the ankle complex. When you perform this motion the sole of the foot is directed away from the midline of the body and the great toe is pointing up slightly.

  • Eversion = abduction + dorsiflexion

 

There is more inversion at the ankle complex, than eversion due the biomechanical arrangement of the bones. 
Muscles of the Foot and Ankle

 
Extrinsic Versus Intrinsic Muscles
There are two types of muscles in the foot and ankle: 
  • the extrinsic muscles 
  • the intrinsic muscles. 

The extrinsic muscles originate on the femur, tibia or fibula above and attach on the bones of the foot via long tendons. All of these muscles cross more than one joint. 

The intrinsic muscles of the foot are short muscles that run between the smaller bones within the foot. Most of these muscles are on the plantar surface (bottom) of the foot and make up the bulk of the sole of the foot.
Muscles that Perform Dorsiflexion

 
There are 4 primary dorsiflexors at the foot and ankle:
  • the tibialis anterior 
  • the extensor hallucis longus 
  • the extensor digitorum longus
  • the peroneus tertius.

 These are all extrinsic muscles located on the anterior aspect of the lower leg and ankle.
Tibialis Anterior- This muscle originates from the lateral condyle and superolateral shaft of the tibia and passes under the *extensor retinaculum to insert on the medial cuneiform bone and the base of the first metatarsal. 

This muscle is the strongest dorsiflexor of the foot and ankle. It also assists with inversion of the ankle. This muscle passes down the front of the lower leg and attaches on the inside (medial) aspect of the foot so when it contracts it pulls the foot up and in.

*The extensor retinaculum is a thin sheath of material that lies over the top of the foot to keep the long tendons of the foot in place. It is visible in the picture to the left. You can see the purple muscle passing under it as it proceeds onto the top of the foot to attach on the base of the first metatarsal. 
Extensor Hallucis Longus- This muscle originates from the central anterior surface of the fibula and the interosseus membrane and attaches to the base of the distal phalanx of the great toe. It extends the great toe (pulls it up), but also assists with dorsiflexion and inversion of the ankle.
Extensor Digitorum Longus- This muscle originates from the lateral tibial condyle, the anterior fibular shaft, and the interosseus membrane. It passes under the extensor retinaculum splits into four parts and attaches to the bases of the distal phalanges of toes II-V. Its primary function is to extend toes II-V (lift them up). It also performs dorsiflexion of the ankle and eversion of the foot.
Peroneus Tertius – This is a small muscle, absent in some people. It arises from the anterior inferior portion of the fibula and attaches on the fifth metatarsal. It performs dorsiflexion and eversion of the ankle.

In the picture to the left it is the smaller, shorter muscle that attaches to the fifth metatarsal.
 

Muscles That Perform Plantarflexion
There are 7 muscles that perform plantarflexion at the foot and ankle: 
  • the gastrocnemius 
  • the soleus 
  • the peroneus longus 
  • the peroneus brevis 
  • the tibialis posterior 
  • the flexor hallucis longus and
  • the flexor digitorum longus
Gastrocnemius – This is a large, bulky muscle in the back of the lower leg and functioning with soleus, are the primary plantar flexors of the ankle. It arises from two heads on the distal posterior femur just above the condyles. It inserts on the posterior/inferior surface of the calcaneus via the Achilles tendon. The Achilles tendon is the strongest tendon in the body, but is also often ruptured.  The gastrocnenius performs plantarflexion at the ankle. Because it also crosses the knee joint above, it performs flexion and medial rotation of the knee.

Soleus – The soleus is a broader, deeper muscle located deep to the gastrocnemius, but it does not cross the knee joint above. It arises from the posterior/superior aspect of the tibia and fibula and merges with the gastrocnemius to insert on the calcalneus via the Achilles tendon. Its primary action is plantar flexion of the ankle especially during walking.

NOTE: Since the gastrocnemius crosses the knee the position of the knee affects its ability to plantar flex the ankle. When the knee is flexed the gastrocnemius is on slack and is not an efficient plantar flexor of the ankle. When the knee is extended the opposite is true.  

To stretch the gastrocnemius you must put stretch across both the ankle and the knee so the foot must be dorsiflexed and the knee extended. To stretch the soleus the foot must be dorsiflexed, but the knee must be flexed to eliminate the gastrocnemius stretch.

 Another important aspect of the gastrocnemius occurs with weight bearing. When the leg is bearing weight and the knee is flexed, the gastrocnenius works with the hamstring in combination to become knee extensors.

Peroneus Longus – This muscle arises from the head and lateral/superior shaft of the fibula. It follows a path down the lateral side of the leg passing behind the lateral malleolus and goes under the lateral aspect of the foot to attach on the plantar surface (bottom) of the foot on the medial cuneiform and the base of the first metatarsal. It performs ankle plantarflexion and eversion.

Peroneus Brevis – This muscle arises from the shaft of the fibular, but more distally on the shaft than peroneus longus. It also passes down the lateral aspect of the lower leg and behind the lateral malleolus to insert on the lateral tubercle of metatarsal V. Unlike peroneus longus, it does not go under the foot. It also performs plantar flexion and eversion of the ankle.

Tibialis Posterior – This is the deepest calf muscle. It originates from the posterior/superior tibial and fibular shafts and the interosseus membrane. It passes posterior to the medial malleolus on the inside of the foot. It attaches primarily to the medial tubercle of the navicular bone, with some smaller attachments to the cuboid, lateral cuneiform, and metatarsal II-IV. It performs plantarflexion, and inversion of the ankle. Since is passes under the medial side of the foot to attach on the plantar surface it also serves to support the arch.
NOTE: The combined attachments of Tibialis Posterior on the medial side of the foot (inside) and the Peroneus Longus on the lateral side of the foot (outside) work together to form a sling across the foot and support the arch.

Flexor Hallucis Longus – This muscle arises from the posterior/inferior fibular and interosseus membrane and runs posterior to the medial malleolus along a groove on the posterior talus, passes to the underside of the foot to attach on the distal phalanx of the great toe. It plantar flexes the great toe (pulls it under), plantar flexes the ankle, and also supports the medial arch of the foot.

Flexor Digitorum Longus – This muscle originates from the posterior/medial tibial shaft and runs posterior to the medial malleolus, also goes to the underside of the foot and attaches on the distal phalanges of toes II-V. Its action is plantar flexion of toes II-V (pulls them under), and inversion of the foot. It also serves as an arch support. 

As you can see from the discussion of the muscles for dorsiflexion and plantar flexion – these same muscles, depending on their location on the foot serve as the muscles that perform inversion and eversion of the ankle as well. Specifically, it splits as follows:
Muscles Performing Inversion of the Ankle:
 The primary muscles that perform ankle inversion are:
  • the tibialis anterior 
  • the tibialis posterior 
  • the extensor hallucis longus 
  • the flexor digitorum longus and 
  • the flexor hallucis longus. 

These are all muscles that run from the lower leg and attach on the medial aspect of the foot. When these muscles contract they pull the insertion toward the origin and thus pull the sole of the foot toward the inside or medial aspect of the body.

 
Muscles Performing Eversion of the Ankle:
The primary muscles that perform ankle eversion are:
  • the peroneus longus
  • the peroneus brevis
  • the peroneus tertius and 
  • the extensor digitorum. 

These are all muscles that run from the lower leg to attach on the lateral aspect of the foot. When these muscles contract they pull the insertion of the muscles toward the origin and thus pull the sole of the foot toward the lateral or outside aspect of the body.

 

NOTE: You will notice that the opposing actions of the foot and ankle are not balanced. Plantar flexion has more muscles that perform this action, and they are more powerful, than the muscles that perform Dorsiflexion. Similarly, there are more muscles that perform Inversion than muscles that perform Eversion at the ankle.

Plantarflexion and Inversion of the ankle are stronger motions than Dorsiflexion and Eversion!

 
Intrinsic Muscles of the Foot

 
These are the smaller, shorter muscles that originate in the foot and attach between the various bones in the foot. It is not within the scope of this course to provide a great deal of detail on these muscles. They will be discussed briefly. There is one intrinsic muscle that lies on the dorsal (top) surface of the foot. The Extensor Digitorum Brevis arises from the calcaneus and attaches on the phalanges of toes II-V. It acts to dorsiflex the toes (pull them up in combination with the extrinsic muscle the extensor digitorum longus already discussed.
The opposite muscle on the plantar (bottom) surface of the foot is the Flexor Digitorum Brevis. It arises from the inferior aspect of the calcaneus and attaches on the middle phalanges II-V. It plantar flexes the middle and proximal phalanges of toes II-V. Its action looks like a “clawfoot” action of scrunching up the toes.
There are similar intrinsic muscles on the dorsum and plantar surfaces of the foot that  flex the great toe, abduct the great toe away from the other toes, move the great toe toward the other toes, and abduct the 5th toe away from the other toes. These muscles originates either on the calcaneus or on the bones of the midfoot and attach on the metatarsals or phalanges of the toes. These muscles include the Flexor Hallucis Brevis, Abductor Hallucis, Adductor Hallucis, and Abductor Digiti Minimi.
The other important intrinsic muscles of the foot are the Lumbricales and the Interossei.

The Lumbricales are four small muscles that run from the flexor digitorum longus tendons up between the metatarsals inside the foot and  attach to the extensor digitorum longus tendons. 

These muscles work to plantar flex the middle phalangeal joints of the foot – to push the toes off the ground during propulsion phase of walking.

 
The Interossei  are the deepest layer of intrinsic muscles and occupy the space between the metatarsals. There are 4 dorsal interossei more on the top of the foot and 4 plantar interossei more on the bottom of the foot. 

They act to plantar flex the proximal phalanges which is also important during the propulsion phase of walking.