What do these gentlemen, this guy, and whoever is planning to use this have in common? Take another look. Yes, that's right. They're all doing or going to do something which involves squatting. When we think about what movements are involved in squatting, most of us immediately think about bending or flexing our knees. But how many of you notice what happens at the ankle joint? This specific position of the ankle joints which is helping these gentlemen stay balanced is known as dorsiflexion and, today, we're going to learn lots more about this as we learn about the functions of the tibialis anterior muscle in 3D.
If you've been following our series of 3D muscle function videos, you will know by now that before getting into the nitty-gritty detail regarding the functions of a muscle, we always take a few moments first to refresh our memories about its anatomy.
The tibialis anterior is one of the three primary muscles of the anterior compartment of the leg, also known as the dorsiflexors of the foot. We got a hint of what dorsiflexion refers to at the beginning of our tutorial but if you can stay with me for a few moments, I'll explain exactly what is meant by the term dorsiflexion as well as what it means to be a dorsiflexor of the foot.
The tibialis anterior is the most medial and superficial of the anterior muscles of the leg lying immediately lateral to the anterior border of the tibia. This makes it particularly easy to find or palpate when learning about the surface anatomy of your leg. Like every other muscle in the body, the tibialis anterior is innervated by a particular nerve which carry sensory information and delivers motor instructions to and from the central nervous system. The nerve in question here is the deep fibular nerve, which is a branch of the common fibular nerve. As its name would suggest, the deep fibular nerve lies deep to the tibialis anterior. It's useful to note the root values of the nerve associated with the muscle we're learning – in this case, the root values of the deep fibular nerve, specifically the muscular branches to the tibialis anterior, are L4 and L5.
The tibialis anterior arises from the lateral condyle of the tibia as well as from the proximal half of the tibial shaft. It also attaches to several soft tissues and fascias in the anterior leg such as the interosseus membrane located here between the tibia and the fibula.
From its origin, the long slender muscular belly of the tibialis anterior descends through the leg tapering off into a tendon in the distal third of the leg. From here, it diverts somewhat medially towards the distal end of the tibia before continuing onto the foot crossing the talus and navicular tarsal bones before inserting into the medial aspects of the medial cuneiform as well as the base of the first metatarsal bone.
Now that we've looked at the attachment sites of the tibialis anterior, it's important for us to identify the joints over which this muscle acts upon. The first joint of interest is, of course, the ankle joint, also known as the talocrural joint, which is formed by the articulation of the medial and lateral malleoli of the tibia and fibula with the superior articular surface or trochlea of the talus bone.
Just below that, we have another important joint which is known as the subtalar joint, also sometimes referred to as the talocalcaneal joint which correctly implies an articulation between the talus and the calcaneus bones of the foot. As the tendon of this muscle crosses over the navicular, medial cuneiform, and first metatarsal bones, the tibialis anterior affects the intertarsal joints. It also affects the first tarsometatarsal joint.
Let's now take all of this information which we've looked at and use it to explore the tibialis anterior muscle from a more functional point of view. As I mentioned at the beginning of this tutorial, the tibialis anterior is part of a group known as the dorsiflexors of the leg, so it's only fitting that our first movement for discussion today is dorsiflexion of the foot at the ankle joint.
When the tibialis anterior contracts, we can see it causes the toes to be drawn upwards towards the anterior leg, which causes the heel to point downwards. Looking at this movement again but from a medial perspective, we can see that dorsiflexion of the foot can be better defined as a motion which causes a decrease in the ankle between the dorsal aspect, or the back of the foot, with the anterior aspect of the leg. You'll remember at the beginning of our tutorial, we mentioned that dorsiflexion of the foot is important when we're assuming a squat position. In this case, however, the foot is stationary, meaning it doesn’t move and the leg is instead pulled forwards over the back of the foot in order to help maintain balance and not fall backwards.
Dorsiflexion is also particularly important in the gait cycle which to you and me is the process of walking. During what's known as the mid-stance phase, contraction of the tibialis anterior causes the body to pivot forward by means of dorsiflexion at the ankle joint. The foot is dorsiflexed again at the end of the swing phase to allow clearance of the foot from the ground helping us to not trip over ourselves.
Moving onto the second function of the tibialis anterior muscle, our next movement of interest is inversion of the foot which is also sometimes referred to as supination of the foot. This movement effectively involves the rolling or tilting of the plantar surface towards the midline. The tibialis anterior works together or synergistically with the tibialis posterior in causing this movement. Taking another look at the foot inversion but this time from a medial view, we can see that it primarily occurs at the subtalar joint, however, movement also occurs at some of the small intertarsal joints of the foot such as the cuneonavicular joint as well as the tarsometatarsal joint of the great toe.
Foot inversion is an important function as it helps to position the foot correctly on the ground preventing overpronation of the foot, which can leave the ankle joint prone to injury especially when running or walking.
Finally, the last function of the tibialis anterior which I'd like to briefly mention is its role in supporting the medial longitudinal arch of the foot, particularly during weightbearing activities such as running and walking.
And with that, we've now explored the main functions of the tibialis anterior, but just in case you miss any of them, let me recap quickly before we finish.
So, in review, we mentioned three main functions of this tibialis anterior muscle. The first function was dorsiflexion of the foot which occurs at the ankle joint also known as the talocrural joint. Next up, we had a look at another function known as inversion of the foot, this time occurring at the subtalar joint. We mentioned here that this movement is also known as supination of the foot. And finally, I briefly spoke about the role of the tibialis anterior in supporting the medial longitudinal arch of the foot especially during weightbearing activities.
And that completes our short tutorial today on the functions of the tibialis anterior muscle. I hope you enjoyed watching. Please be sure to check out our other 3D muscle function videos and lots more at kenhub.com. See you next time!