Ankle Joint

Author: Dr Peter de Souza
Last modified: 17 December 2020

This tutorial is on the ankle joint. The ankle joint is this joint here between the talus, the tibia and the fibula.

It’s a synovial hinge joint and the main movements that you get at this joint are dorsiflexion and plantar flexion.  One way of remembering which way is plantar flexion and dorsiflexion is if you just think of a plant on the floor and you want to squash that plant, you will press down in this direction.  Plantar flexion is squashing a plant movement and dorsiflexion is bringing the toes up to its head.

The distal ends of the fibula and the tibia essentially forms these sockets, which the talus slots into.  On either side of the talus, you’ve got the malleoli.  You’ve got the lateral malleolus of the fibula laterally forming the lateral wall of the socket. Medially, you’ve got the medial malleolus of the tibia forming the medial wall of the socket. And superiorly, the roof to the socket is formed by the inferior surface of the tibia.

I’ve just isolated these two bones, the tibia and the fibula. You can see the riff the socket formed by the inferior surface of the tibia bone and then you’ve got the medial malleolus and the lateral malleolus forming the walls of this socket.  The talus just slots into this socket formed by these two bones.

We’ll just take a quick look at some of the features of the distal tibia and fibula and the talus before going on to talk about the ligaments of this joint.  I pointed out the lateral malleolus of the fibula and the medial malleolus of the tibia. There are some ligaments which bind these two bones together at the distal end.  This is the anterior tibiofibular ligament and this one posteriorly is the posterior tibiofibular ligament.

The bones also are held together by the interosseus membrane as well.  This interosseus membrane is supported distally by these two ligaments.

If I just rotate around to the back, you can see there’s a groove on the back of the tibia on the medial surface. This is a groove for the tendon of the tibialis posterior muscle. You can see this muscle over here running behind that groove.

And then laterally, you’ve got the malleolar fossa on the medial surface of the lateral malleolus and you’ve also got a groove for the fibularis longus muscle, so you can see this muscle running behind that groove or in that groove rather.

We’ll just take a quick look at the talus bone as well. The talus bone obviously articulates above with the tibia and the fibula. Below, it articulates with the calcaneus and anteriorly, it articulates with the navicular.

I’ve just isolated this bone and we’re looking at medially here.  It’s got a head anteriorly, a neck and a body. I’ve rotated it around. This is anterior now up here. You can see the body is slightly wider anteriorly. This means that when the foot is dorsiflexed, the wider, anterior part gets wedged between the two malleoli.

The ankle joint is actually stabler in dorsiflexion. So we’ll take a look at the inferior surface. There are various facets on the inferior surface, which articulate with the calcaneus, but we don’t need to worry about that in this tutorial. The superior surface, you can see it’s kind of dome-shaped. It’s kind of cylindrical. This slots into that socket I showed you before.

The upper surface articulates with the inferior surface of the tibia and this is called the trochlear surface. And then you’ve got the lateral surface which articulates with the lateral malleolus and you’ve got the medial surface, which articulates with the medial malleolus.

The joint capsule of the ankle joint consists of a fibrous and synovial membrane.  The synovial membrane attaches to the margins of these articular surfaces and it contains the articular cavity and the fibrous membrane covers over the synovial membrane.

As with any hinge joint, you’ve got ligaments which line other sides of the joints, so collateral ligaments. The joint is fairly weak at the front and the back, but it’s got strong ligaments on either side.

Medially, you’ve got the medial (deltoid) ligament and laterally, you’ve got three separate lateral ligaments. So the lateral ligaments, you’ve got two ligaments connecting the fibula to the talus.  We’ve got one at the front and one posteriorly. These are called the talofibular ligaments.  Anteriorly, you’ve got the anterior talofibular ligament and posteriorly, you’ve got the posterior talofibular ligament.

And then you’ve got this ligament which connects the medial malleolus inferiorly to the calcaneus.  This ligament is called the calcaneofibular ligament. Those are the three lateral ligaments.

I’ll just rotate the model medially, so we can take a look at the medial complex of ligaments.  The medial ligaments are called the deltoid ligaments because they’re a complex of ligaments which are triangular in shape. This complex of ligaments consists of four separate ligaments.

So the triangular shape isn’t really shown that well here, but if you imagine that these four ligaments that we’re looking at here are blended together and at the apex, they attach to the medial malleolus, they sort of form this triangular shape, which attaches to the navicular, calcaneus and parts of the talus. It’s this triangular shape of ligaments that are blended together.

So you’ve got four parts to this ligament. You’ve got two ligaments which attach from the tibia to the talus. We’ve got an anterior and posterior tibiotalar part. And then you’ve got ligaments which attach to the navicular anteriorly and to the calcaneus inferiorly.  You’ve got a tibionavicular part and a tibiocalcaneal part.

I’ve just switched over to a diagram which shows more quickly the actual triangular shape of this ligaments when they’re blended together. So the medial deltoid ligament consists of four parts. And the word ‘deltoid’, you might remember it from the shoulder muscle, the deltoid muscle, it basically comes from the Greek delta, which is a triangular symbol. So that’s why it’s called the deltoid ligament.

That’s the ankle joint.