Now lets look at the bones. We’ll start by taking a further look at the two long bones of the leg, the tibia and the fibula. The tibia is much the larger of the two bones.
The shafts of the two bones are covered by muscles, except for the anteromedial aspect of the tibia, which lies directly beneath the skin all the way from the knee to the ankle.. The proximal end of the fibula doesn’t form part of the knee joint, but its distal end forms an important part of the ankle joint, as we’ll see.
The tibia and fibula are held together throughout their length by the strong interosseous membrane. Above and below the’re attached at the two tibio-fibular joints. The proximal tibio-fibular joint is a synovial joint, the distal one is a fibrous joint. There’s very little movement at either of these joints. Distally the two bones are strongly held together by the anterior tibio-fibular ligament, and the posterior tibio-fibular ligament.
The projecting ends of the tibia and fibula, which stick out on either side of the ankle, are called the medial malleolus, and the lateral malleolus.
The articular surface for the ankle joint is a broad notch, formed by the curved undersurface of the tibia, and the inner surfaces of the medial malleolus, and the lateral malleolus.
Now let’s look at the bone that articulates with the tibia and fibula to form the ankle joint - the talus. This is the talus. The bone below and behind it is the calcaneus, or heel bone. The bone in front of the talus is the navicular bone. We’ll meet the other tarsal bones shortly. Now we'll go round to the lateral view to see the talus by itself.
This is the head of the talus, this is the neck. The talus has three articular surfaces, one on the head, and one on the underside for the two joints of inversion and eversion, and one on top for the ankle joint.
Here’s the ankle joint. Let’s see how it looks in the living body. Here the loose parts of the joint capsule have been removed, leaving these thickened parts, which are the ligaments of the joint. Here’s the front of the joint in plantar flexion, here’s the back of the joint in dorsiflexion.
On the lateral side, the joint is held together by the posterior talo-fibular
and anterior talo-fibular ligaments. On the medial side it’s held together by this massive ligament, the deltoid ligament, which attaches not only to a broad area on the talus but also to the adjoining bones below and in front, as we’ll see shortly. The ligaments of the ankle joint ensure that the talus can’t rock from side to side like this, or move backward or forward like this, relative to the tibia and fibula.
Here’s the ankle joint with its joint capsule intact, and with the rest of the bones in place. The capsule of the ankle joint is loose on the front, and it’s also loose on the back. This looseness allows for a full range of dorsiflexion and plantar flexion.