Muscles of the anterior and lateral leg

Hello, everyone! This is Joao from Kenhub, and welcome to another tutorial where we’re going to be talking about the anterior and lateral muscles of the leg.

Now, on this tutorial, I'm going to be looking at the different muscles that you can find anteriorly and also laterally on your lower leg. And we’re going to be looking at the different attachment points. So we’re looking at origin points and insertions, and then innervation of the muscles, followed by the functions, the different functions that these muscles will have on the lower leg and also the foot.

Now, before I move on and talk about the different muscles individually, I would like to list them. And before we do so, I want to tell you that the anterior and lateral muscles of the leg can be further divided into two groups. The first group is the anterior extensor group which consists of the tibialis anterior, the extensor digitorum longus muscle, the extensor hallucis longus, and the peroneus tertius.

The other group is known as the lateral fibularis or peroneus group. And keep in mind that fibularis and peroneus mean basically the same thing. So they can be used interchangeably, And you can find some schools using peroneal or peroneus, and other schools using fibularis or fibular in their names when they’re naming structures, especially muscles or… or blood vessels which have these names on their terms.

Now, for this group, we only need to remember two muscles, and these are the fibularis longus and the fibularis brevis.

Starting with the very first one here on our list, we‘re going to talk about, first, the anterior extensor group. And we’re going to talk about, then, the first muscle seen here, highlighted in green. And yes, this is the tibialis anterior. The tibialis anterior has origins, of course—two that you need to remember. The first one is known as the lateral surface of the tibia, as you can clearly see here on this image, which is serving as the origin point for the tibialis anterior. And the other one is found a little bit more posteriorly and known as the interosseous membrane, which is found between the tibia and the fibula and will also serve as an origin point for the tibialis anterior.

And now, we move on to the insertion point of the tibialis anterior. And you can also see here, now, a new image being introduced in this slide, highlighting a bone that will serve as an insertion point for the tibialis anterior. And this will be the plantar side of the medial cuneiform bone which will serve as insertion point for the tibialis anterior. And you can clearly notice here on this image, that is originating here on the tibia and goes all the way, then, to insert on this bone now that is highlighted here on this image, the medial cuneiform bone, specifically on the plantar side of this bone.

Another insertion point for the tibialis anterior will be the first metatarsal bone which is this bone that you can see here on this image right here and will serve as insertion point for this muscle.

When it comes to the innervation of the tibialis anterior, it’s going to happen, thanks to this structure now highlighted here on the left side, as you can see here, highlighted in green. And this is the deep fibular nerve which is a branch of the common fibular nerve, coming from the sciatic nerve and will be innervating the tibialis anterior.

Now, we’re going to move on and talk about the different functions associated to the tibialis anterior. You have probably guessed because now on the right side of the screen, you see the muscle in action and raising in doing something to the foot, and this is what we’re going to talk about next.

Well, in terms of functions, you’re going to see dorsiflexion which is when you lift the back of your foot towards your tibia, and you can see represented by the arrow here on the image. The other function that we’re going to be seeing the tibialis perform is going to be… or known as supination or inversion.

And remember, the insertion at the plantar side of the medial cuneiform bone, when I talked about the insertion points for the tibialis anterior? Well, basically, a supination of the ankle joint is when you lift the medial side and stand on the lateral edge of your foot, as you can also see represented not only by the image but also this arrow here that I just shown you. And this is achieved because the tendon of the muscle goes below the foot and pulls up at the medial cuneiform bone.

And since we’re talking about the different functions associated to the tibialis anterior, it’s important to mention that this muscle is also going to serve as the leading muscle for the supplying structures of the ankle which include the deep fibular nerve, anterior tibial artery, and the anterior tibial vein.

Now, let’s move on to the next muscle on our list. And if you remember correctly, yes, this is the extensor digitorum longus. In terms of origin points, you need to remember three. The first one is going to be the lateral tibial condyle which you can clearly see here on this image. This is the lateral tibial condyle which will serve as an origin point.

The other one is the anterior border of this bone that is hiding a little bit here behind this muscle. This is the fibula. And the anterior border of the fibula will be also an origin point.

The other one is the interosseous membrane that you can see a little bit here. Notice this membrane that you find between the tibia and the fibula and will serve as an origin point for the extensor digitorum longus.

You can sometimes add the head of the fibula as an additional origin point. If you want to write on your exam and do a good job, then don’t forget to also add the head of the fibula as an origin point for this muscle.

We’re going to move on to the insertion points for the extensor digitorum longus. And this muscle goes below the inferior extensor retinaculum. And it divides into four tendons inserting at the dorsal aponeurosis and also at the distal phalanges of the second through fifth toes. And you can clearly see here on this image the different tendons that will be, then, inserting at the distal phalanges and the dorsal aponeurosis.

Now, we’re going to move on to the innervation of this muscle. What you need to know is that, just like the tibialis anterior, the extensor digitorum longus muscle is innervated by the deep fibular nerve.

And it is time for us to move on to the different functions, now seen here also represented by this image on the right side. And in terms of functions, like the other extensors of the lower leg, the extensor digitorum longus is going to be performing dorsiflexion. And if you remember correctly from the tibialis anterior, dorsiflexion is when you lift the back of your foot towards your tibia seen here represented by this arrow.

Additionally, the extensor digitorum longus is going to be performing dorsal extension of the toes from the second to the fifth toe as you can see also here on this image. And it’s not going to be affecting the first toe here, as you can see, because it’s only inserting here on these four toes. So the insertion points are always important when it comes to the movements that these muscles or the actions that these muscles are going to be performing. And you can clearly see here this example—so dorsal extension of the toes when you’re pulling your toes back towards the tibia.

And in opposition to the tibialis anterior that makes supination or causes supination, the extensor digitorum longus muscle forces or produces pronation and seen here represented by this arrow. Pronation or eversion is what we call… this is basically the opposite of supination as we’ve seen on the tibialis anterior. So pronation on the ankle joint is when you lift the lateral side of your foot and stand on the medial edge of the foot as you can clearly see here on this image, so this is the lateral side, the medial side of your foot, and you’re standing on the medial side and lifting the lateral side. And this is what we call pronation or eversion.

We move on, now, to the next muscle on our list, seen also highlighted in green. This is known as the extensor hallucis longus. “Hallucis” is a term for big toe, and “longus,” of course, for long. So you can clearly see this is the long extensor of the big toe.

And in terms of origin points, you need to remember that the extensor of the big toe has its origin at the medial side of the fibula, which you can clearly see here also on this image. This is the fibula hiding here. And the extensor hallucis longus is inserting on or originating on the medial side of this bone.

And also like we’ve seen on the previous muscles, the interosseous membrane, also hidden here a bit, but you can notice a little portion also a little bit below here. This membrane is going to be serving as an origin point for this muscle as well.

Now the muscle is going to go all the way from these two origin points to, then, insert at one point which is the distal phalanx of the big toe. And you can clearly see here: distal phalanx of the big toe which will serve as insertion point for the tendon of the extensor hallucis longus.

Next stop is going to be the innervation of this muscle. And in terms of innervations, just like the other extensors of the lower leg, the extensor hallucis longus muscle is also innervated by the deep fibular nerve.

And we’re going to move on to the different functions of the extensor hallucis longus. And like the other extensors of the leg, it also is going to be performing a dorsiflexion, as you can see here—lifting back your foot towards the tibia—and also dorsal extension of the big toe, as you can see here. So you’re going to be able to lift up your big toe towards the tibia. And it can also be involved in supination and pronation, as you can see here, of the ankle joint depending on the initial position.

Now that we covered the anterior extensor group, it’s time for us to move on to the second group, the fibularis group, that is now seen here represented by the two muscles that we’ve seen on that previous list, the fibularis longus and the fibularis brevis. So these are the fibularis muscles. And these muscles are a group of two muscles at the lower leg, as we’ve seen, and they lie between the peroneal compartment located at the lateral fibular region. And when lowering your foot, they can be easily seen forming the surface of the lateral lower leg.

Now, before we go on into the different details about these muscles, we’re going to just talk about briefly about their innervations, as you can see here on the right image, highlighted in green. This is the nerve that is going to be supplying both of the fibularis muscles. And this is the superficial fibular nerve.

Now, we’re going to start off with the very first one on the list, the fibularis longus. And you can see here that in terms of origin points, it has a long list. And it starts off with the lateral aspect of the fibula which will serve as an origin point, also, the intermuscular septum and the head of the fibular—so these three main origin points that you need to remember.

In terms of insertion points, you need to remember that it will insert at two bones. One is the medial cuneiform bone and the other one is the first metatarsal bone which will serve as an insertion point for the fibularis longus. And you can notice that… it might be a bit confusing here, but if you notice that the muscle is originating here on the fibula and going all the way to then insert, it crosses the foot and goes all the way to insert on the first metatarsal bone as well and the medial cuneiform bone.

Now, let’s take a look at the fibularis brevis. And we need to look at the origin point for this muscle. And what you need to remember here is that it is going to be originating or rising from the fibula. And you can clearly see here on this image, the muscle originating from this bone here: the fibula. And another important note here, especially a topographical note, is that the previous muscle that we talked about, the fibularis longus, is going to be covering this one, the shorter one, the fibularis brevis. So this is important to also add here.

Now, obviously, we’re going to move on and talk about the insertion point for the fibularis brevis. And what you need to know is that this muscle is going to be inserting on the tuberosity of the fifth metatarsal bone.

An important note that I would like to add here about these two muscles that we just discussed is that the tendons of both muscles run caudally towards the foot behind the lateral malleolus and then ventrally along the lateral foot edge. And you can see here on both of these images. There they are lead by two canal-like peroneal retinacula. And the inferior fibular retinaculum stretches between the lateral malleolus and also the calcaneus. The inferior fibular retinaculum stretches between the inferior extensor retinaculum of the anterior muscles of the lower leg and calcaneus.

Now, it is time for us to, now, look at the different functions associated to the fibularis longus and brevis. Now, the fibularis longus and brevis move both the upper and lower ankle joints. And in the upper ankle joint, they will perform depression of the foot, so planter flexion, as their tendons run behind the flexion extension axes. While on the lower ankle joint, their contraction leads to an eversion or pronation, which means that the medial foot edge is lowered whereas the lateral foot edge will be rising.

And still on the functions here, I would like to add a note that, additionally, the tendon of the fibularis longus muscle supports the transverse arch of the foot. So this is an important function here of the fibularis longus.