Meet Valerie – our favorite running track enthusiast. She loves exercising and is getting ready for her morning jog right now. You can see she's busy doing some ankle warm-up exercises which involve rolling her feet outwards like this. Today, we're going to explore a small muscle of the leg which is helping her to do this. But let's just say, if this particular muscle got its way all the time, we'd end up standing like this, which wouldn't be very useful for running, would it? In fact, I imagined it would probably cause quite a bit of pain.
What muscle am I talking about? Let's excuse Valerie for her jog and I'll tell you.
That's right, it's time to discuss the functions of the fibularis brevis muscle.
Before we begin our tutorial, let's first take a moment to discuss the name, fibularis brevis, as some of you may know by its other name – the peroneus brevis. Yes, confusing as it sounds, there are two names for this muscle. Fibularis comes from the Latin word "fibula" while peroneus originates from the Greek word "peronē". Both terms have the same meaning though and refer to pin or prong. Quite appropriate for the long slender bone that's the fibula.
While both fibularis brevis and peroneus brevis are perfectly acceptable, we used the former as it is the more commonly used of the two. I'm sure you know by now that when studying anatomy, form and function go hand in hand. You can't discuss one properly without exploring the other also. So, with that in mind, we're going to begin our study by looking at the form or anatomy of the fibularis brevis muscle.
The fibularis brevis is located in the lateral compartment of the leg where it resides with just one other muscle – its bigger brother, the fibularis longus. And true to its name, the fibularis brevis happens to be the shorter member of this lateral partnership. These two muscles are also known as the evertors of the foot and we'll explore exactly what that means in just a few moments.
Let's begin by talking about its proximal attachment or origin. The origin of the fibularis brevis is located along the distal half of the fibula deep to the fibularis longus. From here, it presents a fusiform or spindle-shaped muscle belly which terminates just before the lateral malleolus of the fibula. Here, it tapers off into a somewhat flat broad tendon which wraps around the lateral malleolus anterior to the tendon of the fibularis longus. It then continues over the lateral aspect of the calcaneus and cuboid tarsal bones running superior to the tendon of the fibularis longus. It finally reaches its distal attachment or insertion near the tuberosity of the base of the fifth metatarsal bone.
Now that we're aware of the anatomy of the fibularis brevis, we can now figure out what joints this muscle acts upon. Identifying these is a key step in understanding the function of any muscle. Our first joint of interest is, of course, the ankle joint which is known as the talocrural joint. We know that this joint is formed by the articulation of the distal ends of the tibia and fibula with the superior surface of the talus bone.
Just inferior to that is our second joint of interest – the subtalar joint. This is also known as the talocalcaneal joint which true to its name involves the articulation between the talus and calcaneus bones.
Also important to know of every muscle is where it gets its mojo from and by mojo, I, of course, mean innervation. The nerve in question here is the superficial fibular nerve which is a branch of the common fibular nerve. And if you really want to melt your anatomy tutor's heart, don't forget to wow them with your knowledge of the root values of the superficial fibular nerve which are L5 to S2.
I think it's fair to say that we're now well and truly informed on the form of the fibularis brevis muscle. That means it's time to turn our attention to the functions of this muscle. And we have just two primary functions to discuss today. These being eversion of the foot at the subtalar joint and plantarflexion of the foot at the ankle joint. Let's continue and find out more about what each of these functions involve.
As I mentioned earlier, the fibularis brevis as well as its larger brother, the fibularis longus, are known as the evertors of the foot. So with that in mind, it's no surprise that our first function of interest here is going to be eversion of the foot occurring at the subtalar joint.
From the neutral position, eversion at the subtalar joint is a relatively limited movement which essentially involves the tilting of the foot outwards or away from the midline. This movement is somewhat limited in its range of motion due to the bony obstruction of the lateral malleolus of the fibula. Eversion of the foot is actually more useful in helping to correct excessive inversion. This means the fibularis brevis helps to move the foot from an inverted position back to the neutral position where it is optimally placed for weightbearing and much less prone to injury. This is extremely important in making sure our feet hit the ground in the correct position during activities such as running and jumping even if not as daring as our friend here.
Moving on now to the second function of the fibularis brevis which is plantarflexion of the foot at the ankle joint. This movement involves the pulling of the plantar aspect or sole of the foot downwards and backwards increasing the angle between the anterior aspect of the leg and the dorsum of the foot. This is possible due to the pulley-like relationship between the tendons of the fibularis brevis and the lateral malleolus of the fibula. Of course, the fibularis brevis is not the primary instigator of this movement but rather a helper to the larger plantarflexors of the posterior compartment.
Plantarflexion is necessary for a whole host of movements such as that necessary to push your foot off the ground when walking or when walking, running or dancing on your tiptoes like this polished ballerina.
And with that, we've explored the functions of the fibularis brevis muscle.
Before I leave you, let me quickly recap to make sure you don't forget any details about the functions of this muscle. We defined two primary functions for the fibularis brevis muscle today. Firstly, we talked about eversion of the foot at the subtalar joint. We saw this involved the tilting of the foot away from the midline elevating the lateral border of the foot.
The second function we discussed was the role of the fibularis brevis in plantarflexion of the foot at the ankle joint. When this occurs, we see the posterior aspect or heel of the foot move towards the posterior of the leg while the toes are moved down in the plantar direction.
Easy peasy, eh? We're down and dusted here now. I hope you've enjoyed this short tutorial on the functions of the fibularis brevis. Please be sure to check out more videos like this one on our website and lots more. See you next time.