The Ankle

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The ankle joint

bones of the ankle

This is a joint between:

the lower end (1) and medial malleolus (2) of the tibia and the lateral malleolus (3) of the fibula

and

the trochlear surface of the talus (4)
(In this illustration the talus is displaced.)



Stability

x-ray ankle fromt view coronal section through ankle and talocalcaneal joints The joint resembles a mortice and tenon joint as used in carpentry. The tibia and fibula must be bound together for the mortice to be stable.
Interosseous membrane and tibiofibular ligament

Stability of the mortice is produced by strong ligamentous ties between the tibia and fibula.

These include:

Only a small amount of movement of the lateral malleolus can be felt even when the foot is raised to its maximum.



Movements of the ankle

Dorsiflexion and plantarflexion
The ankle joint is a synovial hinge joint permitting two movements: Dorsiflexion is a more limited movement (normal range: 10-30°) than plantar flexion (normal range 20-50°).
Muscles and ligaments of dorsiflexion

Ligaments of the ankle


As a hinge joint, the ankle is strengthened at the sides by collateral ligaments.On the medial side, this is the triangular deltoid ligament which radiates from the medial malleolus to (a) the sustentaculum tali of the calcaneus (b) the medial border of the plantar calcaneonavicular ("spring") ligament, (c) the tuberosity of the navicular, (d) the neck of the talus.
bones of the foot with medial ligament attachments indicated
Medial ligament of the ankle

Collig.gif - 62.8 K
On the lateral side, the collateral ligament is also triangular, but in three parts anterior and posterior tibiofibular ligaments and a calcaneofibular ligament.
Collig2.gif - 61.2 K
X-ray of ankle with screw in malleolus X-ray of ankle with fractured tibial malleolus The ligaments of the ankle are very strong. In traumatic injury the malleoli may avulse (break off) while the ligaments remain intact. In addition to stabilising the ankle joint the ligaments also help to bind the calcaneus and navicular to the talus.

Articulating surfaces

talus from 3 angles, showing concave and convex nature The trochlear surface of the talus is a complex shape. It is:
  1. convex anterior to posterior
  2. concave side to side most importantly
  3. broader at the front than the back.

facets of the talus

The facets on the side are triangular (for articulation with the the lateral malleolus) and 'comma-shaped' (for articulation with the medial malleolus).



Talus in dorsi and plantar -flexion

In dorsiflexion the trochlear surface of the talus slides backwards into the mortice formed by the malleoli and the joint becomes close-packed, particularily as the part of the talus going into the mortice is increasingly wider.
By contrast, in plantar flexion the talus slides progressively forwards out of the mortice and movement of the foot as a whole becomes freer.


activity

Plantarflex your foot fully and note how much lateral (side to side) movement the ankle allows in this position.

Now dorsiflex your foot, again noting the degree of lateral movement allowed.

You should find that when dorsiflexed your ankle allows much less movement laterally than when plantarflexed.

The decrease in stability of the ankle when the foot is plantarflexed is one reason why high heels are unstable, and also why you are less stable when walking down hill than walking up hill.


Fainted guardsman When standing erect, the centre of gravity passes in front of the ankle joint (through the midpoint of a line joining the navicular bones.

The tendency to fall forward is normally resisted by activity of the calf muscles (plantarflexors).

Hence Guardsmen (standing to attention on parade) fall forward when they faint.


Summary

Stability

Stability of the ankle joint is provided by:

  1. The bony fit, which is good.
  2. Strong ligaments including:
    1. Those which bind the tibia and fibula resulting in a stable mortice.
    2. The collateral ligaments which also help to bind the talus to the calcaneus and navicular.
    3. The many tendons which pass across the joint.
There is no muscle mass to provide stability around the ankle.

Limitations to movement

Dorsiflexion is limited by tension in the achilles tendon and the posterior part of the collateral ligaments but especially by the bony fit of the joint. At full dorsiflexion, the talus is wedged into the mortice and the joint is close-packed.

Plantar flexion is limited by tension in the tendons lying anterior to the ankle joint and by tension in the anterior parts of the collateral ligaments.



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