Ankle and Foot Anatomy: Bones, Tendons, Biomechanics

The foot and ankle constitute an extraordinary biomechanical complex: 26 bones, 33 joints, and over 100 ligaments and tendons collaborate to fulfill two seemingly opposite functions — to be a stable platform capable of supporting the entire body weight and, at the same time, a flexible lever capable of adapting to irregular surfaces and generating the propulsive force necessary for locomotion.

Understanding the anatomy of the ankle and foot is essential for interpreting common pathologies such as plantar fasciitis, heel spur, Achilles tendon rupture, metatarsalgia, and flat foot, as well as for optimizing prevention and rehabilitation programs.

Table of Contents

• The Ankle Joints
• The 26 Bones of the Foot
• The Plantar Arches
• The Main Tendons
• The Plantar Fascia (Plantar Aponeurosis)
• Biomechanics of Gait
• Innervation of the Foot
• Frequently Asked Questions (FAQ)
• Conclusion
• Frequently Asked Questions
• Resources
• Sources and Scientific References

The Ankle Joints

The ankle joint is a hinge joint formed by the tibia, fibula, and talus bones, located between the lower leg and foot, allowing dorsiflexion and plantarflexion movements. The “ankle” is actually a complex of multiple joints. The two main ones are the tibio-tarsal and subtalar joints, which collaborate to produce the three-dimensional movements of the hindfoot.

Tibio-Tarsal Joint (Talocrural)

The tibio-tarsal joint is a hinge joint (ginglymus) formed by:

• Tibiofibular mortise: the tibia (tibial plafond and medial malleolus) and the fibula (lateral malleolus) form a “clamp” that encloses the talus.
• Trochlea of the talus: the pulley-shaped superior surface of the talus fits into the tibiofibular mortise.

The tibio-tarsal joint primarily allows:

• Dorsiflexion: approximately 20°-30° — bringing the dorsum of the foot closer to the tibia.
• Plantarflexion: approximately 40°-50° — moving the foot away from the tibia (pointing the foot).

Stability is guaranteed by:

• Deltoid ligament (medial): a robust, fan-shaped structure that opposes eversion. Composed of tibionavicular, tibiocalcaneal, anterior tibiotalar, and posterior tibiotalar fibers.
• Lateral ligaments: three distinct ligaments (anterior talofibular, calcaneofibular, posterior talofibular) that oppose inversion. The anterior talofibular ligament is the weakest and most frequently injured in ankle sprains.

Subtalar Joint (Talocalcaneal)

The subtalar joint is located between the inferior surface of the talus and the superior surface of the calcaneus. It allows movements of:

• Inversion: approximately 30° — a combination of supination, adduction, and plantarflexion.
• Eversion: approximately 15°-20° — a combination of pronation, abduction, and dorsiflexion.

The subtalar joint is fundamental for the adaptation of the foot to the ground: on irregular surfaces, the subtalar joint allows the hindfoot to adapt while the rest of the body maintains verticality.

Transverse Tarsal Joint (Chopart’s Joint)

Chopart’s line is formed by two joints that cross the foot transversely:

• Talonavicular (between the talus and navicular)
• Calcaneocuboid (between the calcaneus and cuboid)

These joints amplify the movements of the subtalar joint and are fundamental for the foot’s rigidity/flexibility during walking.

The 26 Bones of the Foot

The foot contains 26 bones (28 if constant sesamoid bones are counted), organized into three regions.

Hindfoot (2 bones)

• Talus: a key bone that connects the foot to the leg, articulating superiorly with the tibia and fibula (tibio-tarsal) and inferiorly with the calcaneus (subtalar). It is the only bone in the foot without direct muscle attachments and has precarious vascularization, making it vulnerable to avascular necrosis in case of fracture.
• Calcaneus: the largest bone of the foot, forming the heel. It receives the insertion of the Achilles tendon posteriorly and supports body weight during the heel strike phase. Its plantar tuberosity is the origin point of the plantar fascia.

Midfoot (5 bones)

• Navicular (tarsal scaphoid): a key medial bone of the medial longitudinal arch. The posterior tibialis tendon inserts on its tuberosity.
• Cuboid: a lateral bone that forms the outer column of the foot. The peroneus longus tendon runs through its groove.
• Three cuneiforms (medial, intermediate, lateral): articulate posteriorly with the navicular and anteriorly with the first three metatarsals.

Forefoot (19 bones)

• 5 metatarsals: long bones that form the body of the forefoot. The first metatarsal is the shortest and most robust, bearing about one-third of the forefoot’s load. The second metatarsal is the longest and least mobile, acting as the axis of the foot.
• 14 phalanges: 2 for the hallux (proximal and distal) and 3 for the other toes (proximal, intermediate, distal).
• Sesamoid bones: two small, constant bones under the head of the first metatarsal, integrated into the flexor hallucis brevis tendon. They protect the flexor hallucis longus tendon and increase its lever arm.

The Plantar Arches

The arches of the foot are fundamental structures that distribute load, absorb impacts, and generate leverage for propulsion. The foot has three main arches.

Medial Longitudinal Arch

This is the highest and most functionally important arch. It extends from the calcaneus to the talus, navicular, medial cuneiform, and first metatarsal.

• Keystone: the navicular bone (or head of the talus).
• Supported by: posterior tibialis tendon (main dynamic stabilizer), plantar calcaneonavicular ligament (“spring ligament”), plantar fascia, long plantar ligament.
• Its reduction defines flat foot; its increase defines pes cavus.

Lateral Longitudinal Arch

Lower than the medial arch, it extends from the calcaneus to the cuboid and fifth metatarsal. It normally rests on the ground during standing.

• Keystone: the cuboid.
• Supported by: peroneus longus tendon, long plantar ligament, plantar calcaneocuboid ligament.
• It functions as a lateral support pillar.

Transverse Arch

It extends transversely at the level of the metatarsal bases, with the second metatarsal as the highest point.

• Supported by: intermetatarsal ligaments, peroneus longus tendon (which crosses the sole of the foot obliquely from lateral to medial), intrinsic foot muscles.
• Its collapse contributes to metatarsalgia and the formation of “flat forefoot.”

The Windlass Mechanism

One of the most elegant mechanisms of foot biomechanics is the windlass mechanism, described by Hicks in 1954:

• The plantar fascia acts like a cable connecting the calcaneus to the proximal phalanges.
• During the push-off phase of gait, dorsiflexion of the toes (especially the hallux) tenses the plantar fascia like a windlass.
• The tension in the fascia “pulls” the calcaneus towards the metatarsal heads, raising the medial longitudinal arch and rigidifying the foot, transforming it from a flexible platform into a rigid lever for propulsion.

This mechanism is compromised in plantar fasciitis and flat foot.

The Main Tendons

Achilles Tendon (Calcaneal Tendon)

The Achilles tendon is the strongest and longest tendon in the body (approximately 15 cm long, 12-15 mm wide). It represents the common tendon of the triceps surae muscle (medial gastrocnemius, lateral gastrocnemius, and soleus) and inserts on the posterior tuberosity of the calcaneus.

• It generates the force for plantarflexion of the ankle, essential for push-off during walking, running, and jumping.
• It can withstand forces up to 12 times body weight during running.
• Approximately 2-6 cm from its calcaneal insertion, it has a hypovascular zone (“watershed zone”) where most tendon ruptures and tendinopathies occur.

Posterior Tibialis

The posterior tibialis is the deepest muscle of the posterior compartment of the leg. Its tendon passes behind the medial malleolus and inserts mainly on the navicular tuberosity, with expansions towards the cuneiforms and the bases of the central metatarsals.

• It is the main dynamic stabilizer of the medial longitudinal arch.
• It controls pronation of the foot during the stance phase.
• Its dysfunction (tendinopathy or rupture) is the most common cause of adult acquired flatfoot.
• Its tendon inverts and plantarflexes the foot.

Peroneal Muscles

The peroneals (peroneus longus and peroneus brevis) occupy the lateral compartment of the leg:

Peroneus longus

• Its tendon passes behind the lateral malleolus, under the foot (in the cuboid groove), and inserts on the base of the first metatarsal and the medial cuneiform.
• Function: eversion, plantarflexion, and stabilization of the first ray. Its course under the sole of the foot contributes to maintaining the transverse arch.

Peroneus brevis

• Its tendon inserts on the base of the fifth metatarsal.
• Function: eversion and lateral ankle stabilization.

Peroneal tendinitis is a common pathology in athletes.

Anterior Tibialis

The anterior tibialis is the main dorsiflexor of the foot. Its tendon crosses the dorsum of the ankle and inserts on the medial cuneiform and the base of the first metatarsal. It controls the descent of the foot after heel contact (eccentric braking) and lifts the foot during the swing phase, preventing tripping.

The Plantar Fascia (Plantar Aponeurosis)

The plantar fascia is a robust band of fibrous connective tissue that extends from the medial tuberosity of the calcaneus to the proximal phalanges of the five toes, with a central, medial, and lateral portion.

Functions:

• Support of the longitudinal arch: like a tie-rod, it maintains tension between the hindfoot and forefoot.
• Windlass mechanism: as described above, it rigidifies the foot during propulsion.
• Shock absorption: its viscoelastic structure dissipates impact forces.
• Protection: it protects the muscles, tendons, and nerves of the sole of the foot.

Plantar fasciitis — the inflammation/degeneration of the fascia at its calcaneal origin — is one of the most common causes of heel pain. A heel spur is a calcification that frequently forms at the origin of the fascia.

Biomechanics of Gait

The gait cycle is the sequence of events that occur from the heel strike of one foot to the subsequent heel strike of the same foot. It is divided into stance phase (60% of the cycle) and swing phase (40%).

Stance Phase

1. Heel Strike

• The calcaneus touches the ground with the foot in slight dorsiflexion and supination.
• The anterior tibialis eccentrically controls the descent of the foot (prevents “foot slap”).
• The heel fat pad absorbs the initial impact (force of approximately 1.2 times body weight).

2. Loading Response

• The foot goes into pronation (subtalar eversion) to absorb impact and adapt to the ground.
• Pronation “unlocks” the transverse tarsal joint, making the foot flexible and adaptable.
• The posterior tibialis eccentrically controls pronation, preventing excessive eversion.

3. Midstance

• Body weight transfers over the supporting foot.
• The foot begins to resupinate (transition from a flexible platform to a rigid structure).
• The triceps surae begins eccentric contraction to control the advancement of the tibia over the talus.

4. Heel Off and Push Off

• The heel lifts, the toes dorsiflex.
• The windlass mechanism activates: dorsiflexion of the toes tenses the plantar fascia, raises the arch, and rigidifies the foot.
• The subtalar joint moves into inversion (supination), “locking” the transverse tarsal joint.
• The triceps surae generates propulsive force through powerful plantarflexion (ground reaction force reaches 115% of body weight).
• The peroneals stabilize the ankle laterally during push-off.

5. Toe Off

• The hallux is the last point of contact with the ground.
• The toe flexors contribute to stability and grip on the ground.

Swing Phase

• The anterior tibialis and toe extensors dorsiflex the foot to prevent tripping (foot clearance).
• The foot repositions in slight supination and dorsiflexion for the next heel strike.

Pronation and Supination: Key Concepts

Excessive pronation (hyperpronation) or prolonged pronation keeps the foot in a condition of excessive flexibility, compromising the propulsive lever and overloading the posterior tibialis, plantar fascia, and medial arch. A pronated foot is a common condition associated with many lower limb pathologies.

Innervation of the Foot

The main nerves of the foot are:

• Posterior tibial nerve: passes behind the medial malleolus in the tarsal tunnel and divides into medial and lateral plantar nerves, innervating the sole of the foot. Its compression in the tarsal tunnel causes tarsal tunnel syndrome.
• Deep fibular nerve: innervates the anterior tibialis and toe extensors; provides sensation to the first interdigital space.
• Superficial fibular nerve: innervates the peroneals and provides sensation to the dorsum of the foot.

Frequently Asked Questions (FAQ)

How many bones does the foot have?
The foot is composed of 26 bones: 2 in the hindfoot (talus and calcaneus), 5 in the midfoot (navicular, cuboid, 3 cuneiforms), and 19 in the forefoot (5 metatarsals and 14 phalanges). If constant sesamoid bones are counted, the total rises to 28.

What is the Achilles tendon and why does it rupture?
The Achilles tendon is the strongest tendon in the body, connecting the triceps surae muscle to the calcaneus. It typically ruptures in the “hypovascular zone” located 2-6 cm above the insertion, where vascularization is reduced. Rupture often occurs during sudden sports activities in individuals with pre-existing tendinopathy.

What are the plantar arches?
The foot has three arches: the medial longitudinal arch (the highest and most important), the lateral longitudinal arch (lower), and the transverse arch. They distribute load, absorb impacts, and generate leverage for propulsion.

What is the windlass mechanism?
It is the mechanism by which dorsiflexion of the toes during the push-off phase of gait tenses the plantar fascia, raising the medial arch and rigidifying the foot. This transforms the foot from a flexible platform into a rigid lever for propulsion.

What is pronation and when does it become a problem?
Pronation (eversion + dorsiflexion + abduction of the foot) is a physiological movement that allows for shock absorption and adaptation to the ground. It becomes problematic when it is excessive or prolonged (hyperpronation), causing overload of the plantar fascia, posterior tibialis, and medial arch.

Why is the posterior tibialis so important?
The posterior tibialis is the main dynamic stabilizer of the medial longitudinal arch. It controls pronation during stance, and its dysfunction is the most common cause of adult acquired flatfoot.

Conclusion

The anatomy of the ankle and foot reveals a structure of astonishing complexity, in which 26 bones, three arches, dozens of ligaments, and a sophisticated system of tendons and muscles collaborate to support body weight, absorb impacts, adapt to the ground, and generate propulsive force for locomotion. From the stability of the tibio-tarsal joint to the adaptability of the subtalar joint, from the support of the plantar arches to the windlass mechanism, each component plays a precise and irreplaceable role.

In case of ankle or foot pain, swelling, instability, gait alterations, or difficulty with footwear, it is advisable to consult your doctor or physical therapist.

Frequently Asked Questions

What is the primary function of the foot and ankle complex?

The foot and ankle complex serves as both a stable platform for supporting body weight and a flexible lever for adapting to irregular surfaces. This intricate design, involving 26 bones, 33 joints, and over 100 ligaments and tendons, enables efficient locomotion and balance.

Why is the subtalar joint considered fundamental for foot function?

The subtalar joint is crucial for the foot’s ability to adapt to varying ground surfaces, which is essential for maintaining body balance during movement. It facilitates pronation and supination, allowing the foot to absorb shock and propel the body forward.

What role do ligaments play in ankle stability, and which one is commonly injured?

Ligaments provide essential stability to the ankle joints by connecting bones and limiting excessive movement. The anterior talofibular ligament is frequently involved in ankle sprains due to its anatomical position and susceptibility to inversion forces.

How does understanding foot and ankle anatomy contribute to injury prevention and rehabilitation?

A comprehensive understanding of foot and ankle anatomy is vital for interpreting common pathologies and developing effective prevention strategies. This knowledge allows physical therapists and healthcare professionals to optimize rehabilitation programs, promoting recovery and reducing recurrence.

Sources and Scientific References

1. He W et al. (2025). Effect of electrical stimulation in the treatment on patients with foot drop after stroke: a systematic review and network meta-analysis. J Stroke Cerebrovasc Dis. 34:108279. DOI | PubMed
2. Noriega DC et al. (2022). Plantar Fasciitis in Soccer Players-A Systemic Review. Int J Environ Res Public Health. 19. DOI | PubMed
3. Mansur NSB et al. (2021). Shockwave Therapy Plus Eccentric Exercises Versus Isolated Eccentric Exercises for Achilles Insertional Tendinopathy: A Double-Blinded Randomized Clinical Trial. J Bone Joint Surg Am. 103:1295-1302. DOI | PubMed
4. Hess GW (2010). Achilles tendon rupture: a review of etiology, population, anatomy, risk factors, and injury prevention. Foot Ankle Spec. 3:29-32. DOI | PubMed
5. Kazemi K et al. (2025). The Effect of Additional Neuromuscular Training on Peri-Ankle Muscle Morphology and Function in Chronic Ankle Instability Subjects: A Randomized Controlled Trial. Sports Health. 17:572-584. DOI | PubMed