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Structure
Intermediate
8 min read

The ankle

The talus is wedged between two malleoli like a tenon in a mortise. The ligaments holding it are not symmetrical, and that asymmetry explains a great deal.
3D scene
The ankle, bones and ligaments
The scene shows the tibia and fibula coming down onto the talus, with the tarsal bones below and the ligaments highlighted on either side. Without the 3D, the picture fits in one sentence: a part wedged between two uprights, held by a thick fan on one side and three thin cords on the other.
Open in the explorer

A tenon in a mortise

The ankle joint — the talocrural — links the tibia and fibula to the talus, the first bone of the foot. The two leg bones come down on either side and form two palpable prominences: the malleoli, medial for the tibia, lateral for the fibula.
Between them the talus is wedged. The comparison with joinery is classic and accurate: a rectangular tenon caught in a mortise, able to move in one direction only.
Ankle mortise
The clamp-shaped space formed by the lower end of the tibia and the two malleoli, into which the talus engages. Its width varies by a few millimetres during movement.
malleolar clamp
That fit explains most of the ankle's behaviour. It is very stable in the plane of flexion — lifting and pointing the foot — and much less so in the others.

Two sides that do not match

The ligaments holding the mortise are not symmetrical, and that is the most useful point on this page.
  • On the medial side, a broad, thick ligament fanning out from the tibial malleolus to the talus, the heel bone and the navicular. It is often called the deltoid ligament because of its shape.
  • On the lateral side, three separate and markedly thinner bands link the fibular malleolus to the talus, in front and behind, and to the heel bone.
That asymmetry is not a design flaw: the lateral malleolus descends lower than the medial one and mechanically blocks outward movement. Restraint against inward movement therefore rests more on the ligaments — the thinner ones.
Certainty level · Established
The medial ligament complex of the ankle is thicker and more continuous than the lateral complex, which is made of three separate bands.
Descriptive anatomy and kinesiology describe the same arrangement and the same asymmetry. What varies between studies is the relative contribution of each lateral band across foot positions.
Standring S (2020) · Neumann DA (2016)

What ankle range changes elsewhere

Dorsiflexion — bringing the top of the foot closer to the shin — is not only an ankle matter. In the squat it is what lets the knee travel over the foot; when it is lacking, the descent is limited or the trunk leans further to compensate.
That is why one squat instruction produces different positions in different people: the range available at the ankle, like the orientation of the socket at the hip, is not the same for everyone.

Seeing the ankle

The ankle, bones and ligaments

The scene shows the tibia and fibula coming down onto the talus, with the tarsal bones below and the ligaments highlighted on either side. Without the 3D, the picture fits in one sentence: a part wedged between two uprights, held by a thick fan on one side and three thin cords on the other.
Current step
The ankle
The talus is wedged between the two malleoli like a tenon in a mortise. On the inner side, a thick fan-shaped ligament; on the outer side, three markedly thinner bands. That asymmetry is no detail: it explains which way the ankle most often gives.
Scene description
A three-dimensional model of four joints from the left side of the body, presented one after another on a paper background. The shoulder shows the shoulder blade, collarbone and upper humerus in bone tones, with the joint capsule, the glenoid labrum and the glenohumeral ligaments in olive grey. The hip shows the hip bone and femur, the capsule wrapping the neck, the acetabular labrum and the three ligaments wound around it. The knee shows the femur, tibia, fibula and kneecap, with the two menisci resting on the tibial plateau, the cruciate ligaments at the centre and the collaterals on either side. The lumbar spine, seen from the side, shows the five vertebrae and the sacrum separated by five discs, with the longitudinal ligaments running in front of and behind the vertebral bodies. The joint tissues are highlighted at each step, the bones staying in the background.
Visible structures
  • Glenoid labrum
    A fibrocartilaginous rim fixed around the edge of the glenoid cavity. It deepens the socket and increases the contact area with the head of the humerus, whose diameter far exceeds that of the cavity.
  • Ligaments of the hip
    Three bands wound around the capsule — iliofemoral, pubofemoral, ischiofemoral. They tighten as the hip extends, which allows standing without continuous muscular effort.
  • Cruciate ligaments
    Two ligaments stretched across the centre of the knee, crossing one in front of the other. They limit the tibia sliding under the femur — forwards for the anterior, backwards for the posterior.
  • Intervertebral discs
    Five discs separate the lumbar vertebrae and the sacrum. Each pairs a tough fibrous ring with a more deformable core, which spreads load and allows slight movement between two neighbouring vertebrae.
  • Ligaments of the elbow
    Two collateral ligaments hold the elbow from the sides, and a ring encircles the head of the radius so it can pivot without leaving its place. The elbow thus combines a hinge and a pivot.
  • Lateral ligaments of the ankle
    Three slender bands link the fibula to the talus and the heel bone. They are markedly thinner than their medial counterparts, which is why the ankle is more easily forced inwards.
Guided steps
  • 1/6
    The head of the humerus is far wider than the socket that receives it. The glenoid labrum deepens the rim, the capsule wraps the whole, and three glenohumeral ligaments reinforce it in front. That is the price of mobility: little bone to hold, a great deal of soft tissue.
  • 2/6
    Unlike the shoulder, the femoral head sits deep in the socket, which the acetabular labrum extends further. The three ligaments wind around the neck and tighten in extension: standing, they carry part of the work the muscles no longer have to supply.
  • 3/6
    Two poorly matched surfaces — the rounded condyles of the femur on an almost flat tibial plateau. The menisci fill the gap, the cruciates hold the tibia front to back, the collaterals hold it side to side. Remove any one of these parts and the load shifts onto the others.
  • 4/6
    Five vertebrae, five discs, and a set of ligaments running the whole height. Each level moves only a few degrees; it is their sum that gives the trunk its range. The longitudinal ligaments limit flexion and extension, the ligamenta flava close the back of the canal.
  • 5/6
    The elbow does two things inside one capsule. The humerus and ulna form a hinge that flexes and extends in a single plane; the head of the radius pivots in place inside a ligamentous ring, which turns the palm over. The two collateral ligaments hold it all from the sides.
  • 6/6
    The talus is wedged between the two malleoli like a tenon in a mortise. On the inner side, a thick fan-shaped ligament; on the outer side, three markedly thinner bands. That asymmetry is no detail: it explains which way the ankle most often gives.
Model licence · Z-Anatomy et BodyParts3D — CC-BY-SA 4.0

What the model simplifies

Limit
What the image is missing
The cartilage is not represented, nor the sheaths that curve around the malleoli and in which the tendons of the calves and tibialis anterior slide. The syndesmosis joining tibia and fibula just above the joint does not appear either.
Above all, the subtalar joint — beneath the talus — produces a large share of inversion and eversion, and is not depicted separately. What feels like an "ankle" movement is in fact spread across several levels.

A subject that calls for care

Caution
What this page does not say
Ankle sprains are among the most common injuries, and the arrangement described above explains why they most often affect the outer side. That allows no conclusion about any particular case.
Body Lab proposes here no test, no exercise and no return-to-activity timeline. An ankle that will no longer take weight, that swells quickly, or that stays painful for several days belongs to a health professional.
The ankle is pointed down by the calves and lifted by tibialis anterior. It works in the squat, the lunge and in every walking step.

Sources

Main sources

  • Standring S (2020). Gray's Anatomy: The Anatomical Basis of Clinical Practice, 42nd edition. Elsevier.
  • Neumann DA (2016). Kinesiology of the Musculoskeletal System: Foundations for Rehabilitation, 3rd edition. Elsevier.
Put it into practice in Shapier

See the calf raise exercise

Open the calf raise entry in Shapier, the exercise that works the calves by pointing the foot down.
See the calf raise exercise
Body Lab explains; Shapier lets you act and track.

Check my understanding

Why is the asymmetry of the ankle ligaments not a design flaw?
When ankle dorsiflexion is lacking in the squat, what happens?
Where does a large share of the foot's inversion and eversion movements come from?
Choose an answer

Read next

  • The knee
    Two poorly matched surfaces, an almost flat plateau under rounded condyles. Menisci, cruciate and collateral ligaments make up for that lack of fit.
    With a 3D scene
  • Tibialis anterior
    Tibialis anterior runs down the front of the shin and lifts the foot. Quiet under load, it works on every step to keep the toes from dragging on the ground.
    With a 3D scene
  • The elbow
    Two mechanisms inside one capsule: a hinge that bends the arm, and a pivot that turns the palm over. The radius rotates in place, held by a ring.
    With a 3D scene

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Trust and method

Author
equipe-editoriale-shapier
Editorial review
Thanh Chau
Scientific review
Pending
Published on
August 2, 2026
Reviewed on August 2, 2026
Next review due August 2, 2027
Limits of this page
  • The model shows neither the cartilage, nor the sheaths in which the tendons curve around the malleoli, nor the syndesmosis joining tibia and fibula just above the joint.
  • The subtalar joint, beneath the talus, produces a large share of inversion and eversion: it is not depicted separately.
  • Ankle sprains are common and take many forms. This page describes an anatomy: it cannot assess a sprain or decide when to resume activity.
  • An ankle that will no longer take weight, that swells quickly, or that stays painful for several days belongs to a health professional.
Sources
  • Standring S (2020). Gray's Anatomy: The Anatomical Basis of Clinical Practice, 42nd edition. Elsevier.
  • Neumann DA (2016). Kinesiology of the Musculoskeletal System: Foundations for Rehabilitation, 3rd edition. Elsevier.
Educational content. Body Lab does not diagnose and does not replace professional advice.
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