The Ankle Joint
The ankle is the joint in the body where the foot meets the leg. Just like many joints in the body, we do not seem to care much about it until something goes wrong. This blog post I am going to talk about the ankle joint and in my next post, I will discuss some of the ankle pathologies or injuries that can occur in this area.
The ankle joint is made up of three bones. The bones are the tibia, fibula and the talus. The tibia and fibula are the bones in the leg and the talus is the bone on the top of the foot. The tibia and fibula make up ‘the mortise’ and talus sits in ‘the mortise’.
The two ankle bones, that we think of, on the inside and outside of the ankle are the tibia and fibula, respectively. ‘The mortise’ is an arch formed by the tibia and fibula. The intersection of these bones connect is called the inferior tibiofibular joint, at the ankle. Around the knee, they meet again at the superior tibiofibular joint.
The inferior tibiofibular joint is held together by ligaments only, no muscles. There is the anterior tibiofibular ligament, in the front. The posterior tibiofibular ligament, in the back. And in between those, is the interosseus membrane. This is the strongest ligament to hold the joint together.
The inferior tibiofibular joint is called a syndesmosis joint. That means that there is no joint fluid to lubricate the joint. But the joint is held together by connective tissue instead.
The talus is an interesting little bone in the foot. Just like the inferior tibiofibular joint, there are no muscles that attach onto the talus.
The talus has a funny shape. It is convex, from front to back, looks like half a circle. While it is concave side-to-side, looks like an indent in the side of the bone. It is what is called a modified sellar joint. A modified sellar joint can only move in one plane of movement. For your ankle, that is top of your foot to the shin = dorsiflexion. And pointing your toes away from the shin = plantar flexion. Basically, this joint can only move the foot up and down. The talus is about 6 mm wide in the front than the back of the bone.
Why is the talus wider in the front than the back. When we bring the top of our foot towards our shin, the talus wedges itself between the inferior tib-fib joint. By the way, the talus and the inferior tib-fib joint = the talocrural joint. Anyways, back to the wedging. When the talus wedges itself between those two leg bones it makes the joint much more stable. So stable in fact that it does not need any muscles to act on the stability of that joint.
When you move your foot up and down, with your leg straight as you sit on the sofa, you do not need a bunch of stability. However, if you are walking, lifting, carrying any weight, you would not want your talus to accidentally slip out of place. That would be bad… actually very bad. Same thing with squatting, as you squat down, the shin will travel forward, essentially bringing the top of your foot towards the shin. If you are squatting and putting something down, again, you want that joint to be very stable.
If there are no muscles holding the talus in its place, why does it not dislocate? There are a lot of ligaments that hold it in place. Ligaments are like pieces of rope. Unlike muscles, ligaments cannot contract to hold the talus in place. Ligaments are little bands of collagen that are very tough. There are multiple ligaments on the inside and outside of the ankle.
On the inside of the ankle are three ligaments that blend together to make one large ligament, called the deltoid ligament. The ligaments have big, scary names but their are mostly named from where they start and end. For example, tibiotalar ligament, starts on the tibia and ends on the talus. The ligaments that form the deltoid ligament are the anterior tibiotalar ligament, tibiocalcaneal ligament and the posterior tibiotalar ligament. They all interact with one another and overlap. Therefore it looks like one big ligament. The deltoid ligament is not nearly as frequently injured as the counterparts on the outside of the ankle.
There are also three ligaments on the outside of the ankle. They are not blended together like the deltoid ligament. From front to back, the ligaments are the anterior talofibular ligament, calcaneofibular ligament and the posterior talofibular ligament. The most commonly injured ligament in the ankle is the anterior talofibular ligament (ATFL), followed by the calcaneofibular ligament (CFL).
These ligaments and muscles from the tibia (shin bone) that go into the foot keep this joint moving properly. Something else that keeps this joint moving is the joint fluid. The talocrural joint is a synovial joint. That means it has a joint capsule that has synovial fluid inside the capsule that helps to lubricate and give nutrition to the cartilage.
I hope you enjoyed learning about the ankle joint. If you have any questions or comments about the ankle joint, please leave a comment below.
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