The human foot and ankle is a complex and highly specialised biomechanical structure. It is composed of at least 28 bones, 33 joints, and more than a hundred muscles, tendons, and ligaments.
We have created a basic guide for our patients to get an insight into the anatomy of the foot and ankle.
The foot is designed to be strong enough to bear the body’s weight, but be flexible enough to allow us to walk, dance and run. This is accomplished by having multiple joints, some which are quite mobile and others that are relatively immobile.
To help us describe the different parts of the foot, we have subdivided it into 3 areas:
Is composed of five toes and the corresponding five proximal long bones (metatarsals). Similar to the fingers of the hand, the bones of the toes are called phalanges and the big toe has two phalanges while the other four toes have three phalanges. The joints between the phalanges are called interphalangeal (IP) joints and those between the metatarsals and phalanges are called metatarsophalangeal (MTP) joints.
Formed by five bones, the cuboid, navicular, and three cuneiform bones. These bones are important in forming the arches of the foot. The midfoot is connected to the hind and forefoot by ligaments, muscles and the plantar fascia.
Composed of the talus and the calcaneum. The two long bones that form the leg, the tibia and fibula, are connected at the top of the talus to form the ankle joint. The talus in turn is also connected to the calcaneum (the heel bone) to form the subtalar joint.
The main bones forming the foot and ankle are shown below:
The ankle as seen from the front
The foot and ankle as seen from the side
The foot as seen from above
These two long bones of the leg, at the distal end, form the ankle joint along with the talus. Both these long bones flare at the bottom to form malleoli. These are commonly injured in ankle fractures.
Model of the ankle joint illustrating the medial (inside) and lateral (outside) malleoli
It is one of the major bones forming the ankle joint. The talus is a very unusual and remarkable bone. It is the second largest bone in the foot and unlike most bones is almost entirely covered in cartilage. Also unusually it has no muscles attaching to it. It therefore “floats” amongst the surrounding bones. The blood supply is different from most other bones as it enters in the far part of the bone as opposed to the nearest part of the bone (retrograde blood supply). This makes the talus vulnerable to healing problems particularly when fractured.
The talus is further subdivided into different parts:
Each of these areas is subject to injury.
The calcaneum is the name for the heel bone. It is the largest bone in the foot. It articulates with the talus to form the subtalar joint and the cuboid bone to form the calcaneocuboid joint. Several foot muscles of the foot originate from this bone.
The calf muscles (gastrocnemius and soleus) insert via the Achilles tendon into the calcaneum at the tuberosity. Several tendons, the tibial artery and nerve pass close to this bone on their way to the rest of the foot. Being the main load bearing bone in the foot, this bone is susceptible to injury from excessive load such as falls from a height. Repetitive stress, from for example long distance running and training, can result in a stress fracture.
The calcaneum is further subdivided into different parts:
The navicular sits in front of the talus on the inner aspect of the foot and forms the joint in front of the ankle joint (talonavicular). The tibialis posterior muscle attaches to the navicular through its tendon at the tuberosity. In approximately 10% of patients there may be an accessory navicular bone. The navicular articulates with the 3 cuneiform bones. Acute trauma can result in navicular fracture while repetitive stress can result in a stress fracture.
The cuboid bone is as the name suggest cuboidal in shape. It sits in front of the calcanuem in the outer (lateral) aspect of the foot. It sits behind the fourth and fifth metatarsal bones. Cuboid fractures are typically associated with jumping sports, but repetitive stress can result in stress fractures.
The 3 cuneiforms are named the medial, middle, and lateral. They form an arch in the midfoot. The medial and lateral cuneiforms project further distally than the middle cuneiform to create a mortise for the base of the second metatarsal that in turn articulates with the middle cuneiform. This creates a keystone effect and contributes to the stability of the midfoot. The medial cuneiform is the largest of the cuneiforms. The tibialis anterior tendon inserts into this bone.
There are 5 metatarsal bones. All share a common shape, with wedge shaped bases that articulate with the midfoot with a long tubular midsection that ends in a rounded head that articulates with the toe.
The 1st metatarsal is the thickest and stoutest of the metatarsal bones although also the shortest. Roughly 40% of the body weight when walking is taken by the 1st metatarsal. On the under surface of the head there are two grooves along which the sesamoid bones glide.
The 2nd metatarsal is the longest of the metatarsals. At its base it is connected to the medial cuneiform by the strong Lisfranc ligament. Injury to this ligament is often missed and can result in significant problems. Problems with the 1st metatarsal result in the load being transferred to the 2nd. As this bone is not designed to cope with this additional load a number of abnormalities can result.
The metatarsals are a common site of stress fractures from repetitive loading activities such as running.
The big toe (hallux) is formed of two bones: the proximal and distal phalanges.
The lesser toes are made up of three bones: proximal, middle and distal phalanges. Several conditions can cause lesser toe problems.
Under the 1st metatarsal head sit two sesamoids, each in its own groove
Under the 1st MTP joint lie two small bones called the sesamoids. These bones are set in the flexor hallucis tendon and form part of the plantar plate of the 1st MTP joint. The largest sesamoid in the body is called the patella (knee cap) and is found around the knee.
Sesamoids are designed to act as a fulcrum or a lever arm for the tendons which surround them. They have an important role to play in normal foot biomechanics, load bearing, reducing friction and providing important shock absorption of the 1st MTP joint.
The sesamoids are meant to glide within the groove under the 1st metatarsal head. In patients with bunions the sesamoids no longer lie correctly within the groove. In patients with arthritis of the sesamoid-metatarsal articulation there is no longer frictionless smooth gliding.
Injury and wear and tear can cause a number of sesamoid problems.
When one bone connects to another it is called a joint. There are different types of joints around the foot and ankle:
Synovial joints can allow a wide variety of possible movements such as:
In the foot and ankle some joints are relatively stiff and immobile, but as a result are more stable. Other joints have greater movement, but are also potentially a lot more unstable, and as a result prone to injury.
Stability can be defined as the body’s ability to bear physiological load and forces without deformation and pain.
Joints rely on both static and dynamic contributions:
Muscles can contract and shorten (concentric) or contract while lengthening (eccentric). Eccentric contraction in particular has an important role in providing dynamic stability.
The main joints found in the foot and ankle are shown below:
The joints of the foot and ankle as seen from the side
The joints of the foot and ankle as seen from an oblique angle
The lesser toes have 2 joints each, the proximal interphalangeal (PIP) and distal interphalangeal (DIP)
The ankle joint is formed by the following bones:
The bony bumps on either side of the ankle joint are called the malleoli and represent the distal flare of the tibia (medial) and fibula (lateral) bones. The posterior malleolus is the name for bottom and posterior part of the tibial bone. One or more malleoli is commonly broken in ankle fractures.
A – lateral foot and ankle x-ray demonstrating the posterior malleolus B – AP (front to back) ankle x-ray demonstrating the medial and lateral malleoli
The primary motion of the joint is in moving the foot up and down (dorsiflexion and plantar flexion). There is also some slight side to side (inversion/eversion) and rotational movement.
Static stability of the ankle is in part due to the anatomical shape of the joint. It is also stabilised by the syndesmosis, lateral and medial ligaments.
Dynamic stability of the joint comes from the muscles. When a muscle contracts, it generates stiffness, which in turn leads to dynamic protection of joints.
Muscles can contract and shorten (concentric) or contract while lengthening (eccentric). The muscles that cross the ankle joint have both concentric and eccentric actions; the latter has an important role in providing dynamic stability.
The peroneal longus and brevis muscles are some of the most important dynamic stabilisers of the ankle and in particular offer protection against lateral ankle sprains.
Further ankle stability is provided by hip abductors (gluteus medius) and knee stabilisers. Good “core” stability is also necessary for a stable ankle.
The subtalar joint is formed by the talus articulating with the calcaneum. The functional anatomy and function of the subtalar joint is still to be fully understood.
It forms complex compound movements with the ankle joint above, and the calcaneocuboid and talonavicular joints in front. It is true to say that the subtalar joint is unique in its function in the foot. The subtalar joint helps “lock” the midfoot during push off stage of the gait cycle. The subtalar joint is important for walking on uneven surfaces.
Illustration of the main hindfoot joints, Ankle, Subtalar, Calcaneocuboid and Talonavicular
The talus, calcaneum, navicular and cuboid bones form three joints, the triple joint:
These 3 joints work in tandem with complex composite actions. In a simplified description they help turn in (invert) and out (evert) the foot.
Damage to one component (bone or joint) can affect the remaining joints in the triple joint.
The midfoot joints include the:
These joints are relatively fixed and immobile. They provide stability and help form the arch of the foot. They also link the hindfoot to the forefoot.
The 1st MTP joint is formed by the articulation of the 1st metatarsal with the proximal hallux.
This is primarily a hinge joint, but there is also some gliding and rotational movement at the 1st MTP joint. The 1st MTP joint withstands approximately 50% of body weight during normal gait and this increases substantially on running and jumping. To withstand these stresses the 1st MTP joint requires stability.
The 1st MTP joint has static and dynamic stabilisers. The bony morphology is inherently unstable due to the shallow joint surface of the proximal hallux. Further static stability is provided by the joint capsule, collateral ligaments, the plantar plate and sesamoid complex.
Dynamic stabilisers include the abductor hallucis, adductor hallucis, extensor hallucis longus and flexor hallucis longus. Injury to this joint is know as a Turf toe.
The lesser MTP joints are formed by the articulation of the metatarsal with the proximal phalanx of the toe.
For further detailed information read Anatomy Of The Lesser Toes below.
There are two joints in the lesser toes:
The anatomy of the lesser toes is complex and a fine balance between all the opposing forces exists in a normal toe. Normal toe function is important for a pain free and fully functional foot.
Bone and joints that make up a normal toe
In the normal toe, a delicate balance exists between the extrinsic (muscles located in the leg that have tendons attaching to the toes) and intrinsic (muscles located in the foot that have tendons attaching to the toes) muscles.
The three main extrinsic muscles and their respective tendons are:
The three main extrinsic tendons and their attachments in the toe
There are many intrinsic foot muscles. They have an important role in stabilising the arches of the foot, controlling pronation and giving dynamic control to the foot.
Important intrinsic muscles controlling the lesser toes are:
On their way to their respective attachments on the toe, the EDL and EDB tendons blend with a structure called the extensor hood at the level of the MTP joint and proximal phalanx. The extensor hood is an important structure in the toe. It is a complex, triangular sheath, with a hood-like appearance, that functions as the tendinous attachment of the extensor digitorum longus but also the intrinsics: lumbrical, plantar interossei, and dorsal interossei muscles. The extensor hood blends into the plantar plate and MTP joint capsule on the undersurface of the toe. Contraction of the intrinsics with the toe in neutral act as flexors of the toe at the MTP joint because the attachment is below the axis of the MTP joint. Due to the attachment of the intrinsics to the extensor hood as they contract, they tighten the extensor hood which in turns straightens the toe at the DIP and PIP joints.
The extensor hood
When the intrinsic muscles contract, the long extensor contraction (EDL) is distributed through the extensor hood equally to all the joints, and as a result the toe is extended (straightened) with DIP & PIP joints straight.
Intrinsic contraction tightens the extensor hood which in turn straightens the DIP and PIP joints
Without intrinsic function, contraction of the long extensors (EDL) produces hyperextension of the MTP joint through the extensor sling, but no extension of the DIP & PIP joints which are then flexed by the long flexors (FDL & FDB).
Result of extrinsic function unopposed by intrinsic activity
The MTP joints are not inherently stable due to the shape of the bones. The metatarsal head is round and the base of the proximal phalanx shaped like a shallow dish.
Alignment of the MTP joints is maintained by both static and dynamic stabilisers. Static stabilising structures include the joint capsule, the collateral ligaments and the plantar plate. Dynamic stabilisers include the flexor and extensor muscles and tendons.
Collateral ligaments that attach the metatarsal head to the proximal phalanx on each side provide some valgus/varus (side to side) stability. The collateral ligament is composed of two main parts, the proper or true collateral ligament that attaches the metatarsal head to the base of the proximal phalanx, and the accessory collateral which inserts on the plantar plate.
Lateral collateral ligament
The plantar plate and plantar fascia resist upward (dorsal) displacement of the toe. The plantar plate is a fibrocartilaginous thickening of the plantar capsule of the MTP joint. This is continuous with the periosteum (surface layer on bone) of the base of the proximal phalanx. It is attached to the metatarsal head by the collateral ligament.
The plantar plate
Ligaments are fibrous structures that provide stability to joints. They join one bone to another.
The foot as viewed from above, the structures in blue represent ligaments and joint capsules which hold bones together
Foot & ankle ligaments viewed from the outer (lateral) aspect
Foot & ankle ligaments viewed from the inside (medial)
Technically the syndesmosis is a joint, however it also has 4 key ligamentous constituent parts. It provides stability to the ankle joint by holding together the distal tibia and fibula and resists rotational, translational and axial forces.
The above complex of ligaments can be injured in a high ankle sprain.
Three ligaments: ATFL, CFL and PTFL form the lateral ankle ligaments. They provide stability to the ankle joint and prevent the ankle rolling inwards (inversion).
The ATFL is one of the most commonly injured ligaments around the ankle and a frequent cause of lateral ligament instability. The ATFL is prone to injury when the foot is pointing down (plantar flexed) and turned in (inversion).
The second most commonly injured ligament is the CFL. Injury to this ligament can exacerbate instability of the ankle and cause subtalar instability as well.
These are the largest ligaments in the foot & ankle and are the most important stabilisers of the ankle joint. They include the Deltoid and Spring ligament complexes.
The deep deltoid ligament prevents lateral displacement of the talus (talar shift) and prevents external rotation of the talus. The superficial deltoid ligament primarily resists eversion of the hindfoot. Injury to this ligament cause pain on the inside of the ankle with instability.
The Spring ligament is a very important structure which helps to maintain the arch (medial longitudinal arch) of the foot as well as supporting the head of the talus during weight bearing. Injury to this ligament, can result in progressive flat foot deformity of the foot and pain.
The Lisfranc ligament is an important ligament that connects the medial cuneiform to the base of the 2nd metatarsal. This connection maintains proper alignment between the metatarsal and the midfoot bones. The ligament can be injured either by a sprain or a fracture, and is often missed, resulting in chronic problems.
The plantar plate ligament is a fibrocartilaginous thickening of the plantar capsule of the MTP joint. It is continuous with the periosteum (surface layer on bone) of the base of the proximal phalanx. It is attached to the metatarsal head by the collateral ligaments (true collateral and accessory collateral). The plantar plate and plantar fascia provide stability by resisting upward (dorsal) displacement of the toe.
In the 1st MTP joint the medial and lateral sesamoid are firmly embedded within the plantar plate.
Injury to this ligament is believed to play a role in the development of MTP joint instability and crossover toe deformity.
Muscles are bundle of fibrous tissue that have the ability to contract and as a result producing movement, power and maintaining the posture of the body. Tendons are structures that attach a muscle to a bone. In the foot and ankle tendons are named after the muscles that power them with the exception of the Tendon Achilles.
The muscles acting on the foot can be classified into extrinsic muscles, those originating on the anterior or posterior aspect of the lower leg, and intrinsic muscles, originating on the dorsal (top) or plantar (base) aspects of the foot.
The gastrocnemius is an exception in that it originates from the back of the thigh bone (distal femur) just above the knee and inserts into the heel bone (calcaneum).
This powerful calf muscle has two heads, medial and lateral which originate at the back of the distal thigh bone (femur) and inserts into the heel bone (calcaneum) distally.
The gastrocnemius is mainly involved in running, jumping and other powerful fast movements of the leg.
Along with the soleus muscle it forms the calf muscle also known as Triceps Surae. The function of the gastrocnemius is to bend the the foot and ankle downwards so that the toes are pointing (plantar flexion).
Forced dorsiflexion of the foot can result in injury to this muscle.
This muscle originates on the leg bone (tibia) below the knee and lies under the gastrocnemius muscle. It blends into the gastrocnemius muscle distally to become the Achilles tendon. Similar to the gastrocnemius muscle its primary motor function is to plantar flex the foot.
The soleus is mainly involved in walking, dancing and maintaining the standing posture. It also has an important role in pumping blood from the leg back to the heart.
This is a small muscle that originates along the lateral head of gastrocnemius. It has the longest tendon in the body. It is a weak plantar flexor of the foot. It can be injured in sports.
The Achilles tendon is formed at the mid calf by the gastrocnemius and soleus muscles and inserts into the calcaneum. It is the strongest and largest tendon in the body.
The Achilles tendon is subjected to the highest loads in the body. The tension across the tendon can be up to eight times body weight during running and jumping and four times during walking.
Through the Achilles tendon, the gastrocnemius and soleus muscles plantarflex the foot at the ankle joint. This movement will make the foot point down.
The tendon has 3 parts:
The blood supply to the Achilles tendon is poorer than other parts of the body. It receives blood (tibial artery) proximally by the muscles attached to the tendon and distally where it inserts into the heel bone. In the middle the blood supply (peroneal artery) is weakest and not surprisingly an area prone to injury and damage. The Achilles tendon has a soft tissue envelope called the paratenon. The middle of the Achilles tendon receives its blood supply through this tissue although it is sparse. The paratenon allows the Achilles tendon to glide up to 1.5cm.
In front of the Achilles tendon lies Kager’s fat pad which has an important role in the function and protection of the Achilles.
The anatomy of the Achilles tendon on MRI
The tibialis posterior muscle originates on the posterior borders of the tibia and fibula (beneath the calf muscles in the posterior compartment of the leg). As it descends into the foot it winds behind the media malleolus of the ankle.
Its main insertion is into the navicular tuberosity and medial cuneiform. Further slips of the tendon insert into the base of the 2nd, 3rd and 4th metatarsals, intermediate and lateral cuneiforms and cuboid bone.
Tibialis posterior muscle and tendon have an important role in maintaining and supporting the medial arch of the foot.
Contraction of tibialis posterior inverts (turns in) and plantar flexes (points down) the foot at the ankle.
Dysfunction of the tibialis posterior, including rupture of the tibialis posterior tendon, can lead to the development of flat feet in adults.
Tibialis anterior muscle originates in the upper two thirds of the outside (lateral) surface of the shin bone (tibia). The tendon inserts into the medial cuneiform and first metatarsal bones of the foot.
It acts to bring the foot up (dorsiflex) and turn in (invert) the foot.
Injury to the common peroneal nerve supplying tibialis anterior or the tendon itself will result in a drop foot.
Peroneus brevis muscle arises from the lower two thirds of the outside (lateral) surface of the fibula.The tendon runs behind the outer aspect of the ankle (lateral malleolus). It then runs forward on the lateral side of the calcaneus, above the tendon of the peroneus longus, and is inserted into the tuberosity at the base of the fifth metatarsal bone.
Peroneus brevis turns the foot out (everts) and provides dynamic stability to the lateral aspect of the foot and ankle. A severe sprain and inversion injury can damage the tendon.
A – Peroneus brevis tendon B – Peroneus longus tendon
Peroneus longus originates more proximal to peroneus brevis on the fibula. It also runs posteriorly around the lateral malleolus of the ankle, then continues under the foot to attach to the medial cuneiform and first metatarsal.
The primary role of peroneus longus is to plantar flex the 1st ray. It also plantar flexes and everts the foot. It also helps maintain the transverse arch of the foot and provides lateral dynamic stability to the ankle..
The flexor hallucis longus muscle originates in the back of the leg (posterior compartment) and inserts into the undersurface (plantar aspect) of the big toe (distal phalanx).
Its function is to bend (plantar flex) and invert the foot. It also bends (plantar flexes) the big toe.
The extensor hallucis longus is a muscle, situated between the tibialis anterior and the extensor digitorum longus in the anterior compartment of the leg and inserts into the base of the distal hallux of the big toe. The extensor hallucis longus extends (straightens and lifts up) the big toe, dorsiflexes the foot, and assists with foot eversion and inversion.
This muscle is one of 3 muscles that originate in the back of the leg (posterior compartment), the other two being flexor hallucis longus and tibialis posterior. It inserts into the undersurface (plantar aspect) of the lesser toes (distal phalanx).
The flexor digitorum longus flexes (bends) the lesser toes.
This extensor digitorum longus originates form a broad surface including the anterior aspect of the tibia, fibula and interosseous membrane. In the foot it divides into 4 tendon which insert in the 4 lesser toes. As each tendon crosses the lesser MTP joint it divides into 3 slips, the central slip inserts into the base of the middle phalanx and the two lateral slips unite and insert onto the distal phalanx of the toe.
The main action of the extensor digitorum longus is to extend the toe. However it can be recruited to help dorsiflex the foot at the ankle if need be.
The flexor digitorum brevis originates on the inside (medial) process of the calcaneus and central part of the plantar fasica. It inserts into the all 4 of the lesser toes. At the level of MTP joint each tendon divides into two limbs which pass around the flexor digitorum longus tendon, and finally join to insert into the middle phalanges of 2nd to 5th toes.
The flexor digitorum brevis bends (plantar flexes) the middle phalanges at the PIP joint. As it continues to contract the proximal phalange flexes at the MTP joint.
The lumbricals are 4 small muscles that arise from the 4 flexor digitorum tendons in the foot. Each of the lumbrical tendons inserts into the expansions of the tendons of the extensor digitorum longus on the dorsal surfaces of the proximal phalanges. All four lumbricals insert therefore into the extensor hoods of the phalanges. As a result contraction of the lumbricals causes extension at the inter-phalangeal (PIP and DIP) joints. However as the tendons also pass inferior to the metatarsal phalangeal (MTP) joint axis, it also creates flexion at this joint.
There are dorsal and plantar interossei muscles of the foot.
The 4 dorsal interossei muscles originate from the proximal half of the sides of adjacent metatarsal bones. The tendons are inserted on the bases of the 2nd, 3rd and 4th proximal phalanges and into the aponeurosis of the tendons of the extensor digitorum longus without attaching to the extensor hoods of the toes.
The dorsal interossei help spread the lesser toes (abduct) and along with the plantar interossei help bend (flex) the toe at the MTP joint.
The 3 plantar interossei muscles originate from metatarsals 3-5. They bring the toes together (adduction).
Together the dorsal and plantar interossei stabilise the lesser toes. They also help maintain the anterior metatarsal arch of the foot and also to a lesser degree the medial and lateral longitudinal arches of the foot.
Nerves provide the foot and ankle with sensation. They also tell the muscles when to contract and when to relax.
Sensory innervation of the foot
This nerve runs through the lateral compartment of the leg and supplies the muscles within it, the peroneus longus and brevis. It also innervates the majority of the skin on the dorsum of foot, excluding the webspace between the big toe (hallux) and second toe are supplied by the deep peroneal nerve.
This nerve runs through extensor digitorum longus and down the interosseous membrane. It then crosses the tibia and enters the top (dorsum) of the foot. It innervates the muscles in the anterior compartment of the leg and the dorsum of the foot. It also supplies a small region of skin between the big and second toes.
This nerve is a branch of the sciatic nerve. It runs down the leg, between the two heads of the calf muscle (gastrocnemius). It curves behind the inside of the ankle (medial malleolus) and continues into the foot. It supplies all the muscles in the posterior compartment of the leg. It also supplies all the sensation to the sole (plantar) of the foot.
This nerve is a branch of the femoral nerve and runs down the inside of the leg to the inside (medial) part of the foot and innervates the skin on the medial side of the ankle and foot.
This nerve also runs between the heads of the gastrocnemius, but it runs under the lateral malleolus (outside of the ankle). It innervates the skin on the outer aspect (lateral) of the leg and foot.
These nerves branch off the medial and lateral planter nerves. They innervate the skin and nail beds of the toes.
The plantar fascia is a thin layer of fibrous tissue supporting the arch of the foot. It originates from the undersurface of the calcaneum and spreads distally into each of the 5 toes. As it does so it divides into a superficial and deep layer. The superficial layer is intimately related to the tissues under the skin and the fat pad. The deep layer is attached to the plantar plate.
The Achilles tendon has a continuous fascial connection with the plantar fascia of the foot. Tension in the Achilles tendon will therefore cause tension in the plantar fascia.
The plantar fascia has multiple functions. It supports the arch of the foot. It also bears roughly 15% of the load in the foot. During walking and standing the plantar fascia stretches and behaves like a spring. The plantar fascia also contributes to the “windlass mechanism“.
The term ‘windlass’ comes from sailing, describing the winch mechanism where the rope is wound around a drum. The plantar fascia simulates a cable attached to the calcaneus and the metatarsophalangeal joints. Dorsiflexion of the toes during the propulsion phase of gait winds the plantar fascia around the head of the metatarsal. This winding of the plantar fascia shortens the distance between the calcaneus and metatarsals to elevate the medial longitudinal arch and allows the foot to act as an efficient lever.
As body weight is applied to the foot, the plantar fascia is placed under tension. Stretch tension from the plantar fascia prevents the splaying of the calcaneus and the metatarsals and maintains the medial longitudinal arch.
The plantar fascia (yellow line) prevents collapse of the foot arch by virtue of its anatomical orientation and tensile strength (yellow arrows), body weight (red arrow) ground reaction force (blue arrow)
The plantar fascia (white arrow) Achilles tendon (red arrow) and continuous fibres (yellow arrow)
An arch is defined as a “curved symmetrical structure spanning an opening and typically supporting the weight of a bridge, roof, or wall above it”.
In the foot there are several arches which share a curved shape and biomechanically allow the foot to support the weight of the body at rest, standing and running. The arches of the foot are formed by the tarsal and metatarsal bones and, strengthened by ligaments, tendons and the plantar fascia.
The medial longitudinal arch of the foot
The arches of the foot can be described as:
As well as supporting the weight of the body, the medial arch in particular also acts as a spring thus spreading the load across the foot and minimising wear and tear of the structures. They can also store the energy of the forces involved with walking, returning it at the next step and as a result reduce the energy expenditure of walking and running.
The transverse arch of the foot
The shape of a persons foot and in particular their arches can give an indication to the types of conditions and injuries that person may be susceptible to. A person with a low longitudinal arch will have a flat foot (pes planus), and likely stand and walk with their foot rolled inwards (pronated position). Potential problems include heel pain, plantar fasciitis and medial arch pain and cramps. Flat footed people may also have more difficulty performing exercises that require supporting their weight on their toes. Over pronation of the foot is also associated with knee pain and thigh pain.
People who have always had flat feet all their lives, are unlikely on the whole to develop problems. People who acquire flat feet or only have one flat foot (asymmetrical changes) tend to have an underlying foot condition that warrants investigation and possible treatment.
People who have high longitudinal arch or a cavus foot, tend to walk and stand with their foot in a rolled out (supinated position). High arches can also cause plantar fasciitis as it places increased strain on the plantar fascia. People with cavus foot are also at risk of ankle instability and 5th metatarsal stress lesions and fractures.
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