The ankle joint is a critical piece of our body for supporting functional movement. It’s part of what allows us to respond to walking or running on different types and uneven surfaces. It’s also a necessary component of other types of movement like jumping and kicking. And it also helps us maintain our balance and shift our weight as we’re doing all of those kinds of movements.

So, as you might imagine, the ankle is complicated. In fact, if we include all the structures of the foot and ankle together, we have 28 bones, 34 muscles, and 112 ligaments that come together to create the whole tensegrity of our foot and ankle. Let’s take a look at the structures that make up the ankle joint specifically, and the actions that happen there.

What structures make up the ankle?

It’s important to understand that what we refer to as the ankle joint, is actually two joints. These two main joints work together to create the wide range of movements that we need at our ankles. The combination of movements from these two joints allows us to adapt to all kinds of different terrain under our feet. Additionally, we have a series of muscles and ligaments that surround and connect each of these two joints, and connect the bones within these joints to other bones in the foot. These muscles and ligaments are critical for maintaining the balance between mobility and stability that we need. 

Bones in the ankle

The tibia, fibula, talus, and calcaneus are all important bones to know when thinking about the ankle joint. What we often think of as the ankle is really more than one joint. So it’s important to know where these bones are and how they relate to one another to understand function and dysfunction at the ankle.

The tibia is the larger of our lower leg bones. The fibula is the smaller of our lower leg bones. The talus is a wedge-shaped bone that is wider in the front than in the back. It sits just underneath the tibia and fibula and on top of the calcaneus. The calcaneus is our heel bone. It sits underneath (distal) and extends behind (posterior) the talus.

Joints at the ankle

The two main joints that make up what we think of as the ankle are the tibiotalar joint (also called the talocrural joint) and the subtalar joint. In practice, there are also additional articulations of bones of the foot that contribute to the full range of motion in our ankles and feet that I won’t go into in this article. Our ankles are complicated! 

Tibiotalar joint

The tibiotalar joint is located where the tibia and the fibula meet the talus. The rounded bony prominence on the lateral side of our ankle (called the lateral malleolus) is the bottom of the fibula where it meets the talus. The rounded bony prominence on the medial side of our ankle (called the medial malleolus) is the bottom of the tibia where it meets the talus.

The shape of the bones helps create a snug fit between the tibia, fibula, and talus. The way the malleoli of the ankle hug the tarsal bone creates a sort of biomechanical version of a mortise, like the way a perfectly shaped tab on a piece of wood inserts snugly into a hole to join to sections on a piece of furniture. You can imagine how that would add some stability to what can be a very mobile part of our body. 

The tibiotalar joint is a hinge joint. It is responsible for the hinging movements at our ankle joint. It does dorsiflexion and plantarflexion of the foot at the ankle.

Subtalar joint

We have a second joint that is necessary for the full range of movements we use at the ankle. The subtalar joint is located where the talus meets the calcaneus. It’s a gliding joint. It’s this joint that allows us to tilt our foot medially and laterally in eversion and inversion at the ankle.

Movements at the ankle

The main movements that we do at our ankle joints are:

• Plantarflexion
• Dorsiflexion
• Eversion
• Inversion

Plantarflexion and dorsiflexion happen at the tibiotalar joint. Plantarflexion happens when we point our foot (like stepping on a gas pedal). Dorsiflexion happens when we flex our ankle to bring the foot up toward our body (like when we heel strike while walking). Eversion and inversion happen at the subtalar joint. Eversion happens when our foot rolls in to bring the big-toe side of our foot closer to the ground. Inversion happens when we roll our foot out to bring the pinky-toe side of our foot closer to the ground. 

You might have also heard the terms supination and pronation used in relation to the ankle. Supination and pronation are actually combinations of plantarflexion/dorsiflexion and eversion/inversion that happen during movement. It’s normal for our ankles to move in and out of moments of supination and pronation as we walk. However, if we have an excess of either supination or pronation and our ankle doesn’t return to neutral in a static standing position, then that can indicate an imbalance in the connective tissues, an injury, or some other kind of issue with the ankle.

Muscles at the ankle joint

The ankle joint is one key place in our lower body kinetic chain that makes it possible for us to respond to all the changes that can happen in the ground beneath us. In order to provide that adaptability, there are a lot of structures that help hold the ankle joint together while allowing it to move in many different directions. 

Let’s take a look at the muscles that cross the ankle joint.

Muscles that move (or assist) the ankle into plantarflexion:

• Gastrocnemius
• Soleus
• Plantaris 
• Tibialis posterior
• Flexor digitorum longus
• Flexor hallucis longus 
• Fibularis longus
• Fibularis brevis 

Muscles that move (or assist) the ankle into dorsiflexion:

• Tibialis anterior
• Extensor digitorum longus
• Extensor hallucis longus
• Fibularis tertius

Muscles that move (or assist) the ankle into eversion:

• Fibularis longus
• Fibularis brevis
• Fibularis tertius

Muscles that move (or assist) the ankle into inversion:

• Tibialis anterior
• Tibialis posterior

Ligaments

As much as we need many directions of mobility and adaptability at the ankle joint, we also need stability. Most of our body weight is passing through our ankles as we stand and walk. When we add momentum into the equation, by running or jumping for example, then we need even more stability at our ankle joints.

One of the sources of that stability is a series of ligaments that fan out in many different directions to help hold things together at the ankle. Our ligaments work with our muscles and other soft tissue to help distribute load in a balanced way as we move. This makes our foot and ankle a great example of tensegrity!

Major ligaments of the tibiotalar and subtalar joints

(Many of these ligaments can be separated into more than one distinct band which also have names, but are beyond the scope of this article.)

• Deltoid ligament—this ligament connects the tibia to the navicular, calcaneus, and the talus
• Anterior talofibular ligament—this ligament connects the talus to the fibula
• Posterior talofibular ligament—this ligament connects the talus to the fibula
• Calcaneofibular ligament—this ligament connects the fibula to the calcaneus
• Lateral, medial, and posterior branches of the talocalcaneal ligament—these connect the talus to the calcaneus
• Interosseous talocalcaneal ligament—this ligament connects the talus to the calcaneus
• Anterior (or cervical) talocalcaneal ligament—this ligament connects the talus to the calcaneus

Conclusion

The ankle is a complex area of joints, muscles, and ligaments that allows us to be highly adaptable as we move over many different kinds of surfaces. We need healthy functioning ankle joints for walking, running, jumping and so many activities we do on our feet.

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