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Functions and anatomy of the extensor hallucis longus muscle shown with 3D model animation.
Take a look at the toe movements shown on the screen. Quite boring, isn't it? You might wonder why we're dedicating an entire video to something that is the size of a quarter of a dollar bill and just moves up and down. We'll despite smacking it against every corner and edge of your home, your big toe or hallux is a very important part of your foot. In fact, without it, you probably wouldn't have been able to walk very well to your desk in order to watch this video.
Luckily, such unfortunate events like banging your toe off everything and tripping yourself up are avoided thanks to muscles like your extensor hallucis longus, and you'll learn all about its functions in the next few minutes. As our 3D model on the screen proudly showcases, the extensor hallucis longus is generally located on the anterior or ventral side of the leg. In fancy anatomy terms, we can more specifically describe it as being part of the anterior compartment of the leg which is also known as the dorsiflexor compartment due to many muscles being involved in dorsiflexing your foot. But we'll speak more about that in a few moments.
You can see on the screen that the extensor hallucis longus muscle is buried underneath other larger ones of this region, so it is located quite deep within the anterior compartment. Before learning what's up with this muscle, we'll have a look at who or should I say what excited to contract in order to perform its function. The guilty nerve in question here is the deep fibular or peroneal nerve whose fibers are derived from the fourth and fifth lumbar segments of the spinal cord with most of the muscle's innervation coming from the L5 nerve root.
At Kenhub, we try to make your learning as easy as possible, therefore, I'm going to show you the attachments of the extensor hallucis longus first. Because if you can get your head around this aspect, the functions become intuitive with no memorization required whatsoever.
As you can see on the screen, the extensor hallucis longus originates from two places – the middle portion of the anterior surface of the fibula which you can see here and the interosseus membrane which is this band of fibers connecting the tibia and the fibula. Emerging from between the tibialis anterior and extensor digitorum longus, the extensor hallucis longus travels inferiorly in the anterior compartment of the leg until the distal third of the leg. Here, it appears at the surface and passes underneath the superior extensor retinaculum and through the inferior extensor retinaculum of the foot. It then follows the crest of the dorsum or back of the foot all the way towards the great toe where it inserts onto the dorsal aspect of the base of its distal phalanx.
Now that we've seen where the extensor hallucis longus attaches, understanding what joints it moves will be a piece of cake. The main fulcrums around which the muscles act are the ankle joint together with the metatarsophalangeal and interphalangeal joints of the big toe. The ankle joint, also called the talocrural joint, is the connection point between the distal ends of the tibia and the fibula and the superior part of the talus.
The metatarsophalangeal joint of the great toe which you can see highlighted for you on the screen is easy to keep in mind because you'll find it exactly where its name says it will be. That's right, it is the junction between the first metatarsal and proximal phalanx of the big toe itself. Following the same trail of thought, the interphalangeal joint is found between the proximal and distal phalanges of the hallux.
Now that we've seen its origins, insertions and joints of the extensor hallucis longus separately, let's put all those pieces together and see the entire picture – the movements that the extensor hallucis longus is responsible for.
There are two main ones this muscle is capable of producing – extension of the hallux or great toe which is the most important one and dorsiflexion of the foot. Let's dissect each movement one at a time and ask our model on the screen to show them to us.
Extension of the great toe or hallux happens around both the metatarsophalangeal and interphalangeal joints. It involves the movement of the hallux in an inferior to superior direction reducing the angle between the toe and the dorsum or the top part of the foot. Beginning first with the toe in the flexed position, contraction of the extensor hallucis longus causes extension of the hallux to occur returning it to the neutral position exactly like you see happening right now on your screen. From the neutral position, extension of the hallux continues in the same inferior to superior direction reducing the angle between the great toe and the dorsum of the foot even more. This may also be referred to as hyperextension or dorsiflexion of the hallux.
But what do you need this movement for? Well, first of all, without the extensor hallucis longus to antagonize hallux flexion, you would permanently up like this, which although is nice when curling your toes up in bed, is not the most functional use of your toe if you can't extend it. In addition to this, you actually need to extend your great toe when you walk.
Looking again at our video from the beginning of our tutorial, you can see that extension of the hallux places tension on the plantar fascia of the foot stabilizing it and providing support to the medial longitudinal arch of the foot. This is important in the push off phase of walking.
So there you have it, the first and most important function of the extensor hallucis longus muscle – hallux extension.
The second movement this muscle contributes to is dorsiflexion which happens around the ankle joint. As the name itself suggests, dorsiflexion involves moving the foot from an inferior to superior position towards the dorsum of the foot, simply known as the back or top part of the foot. Let's take advantage of our model over here and see how this looks.
When you dorsiflex the foot, the angle between the toe and the anterior portion of the leg is reduced bringing them closer together. And why do you need to dorsiflex your ankle? The situations when this is necessary are more straightforward to think about than hallux extension.
For example, your ankle passes through phases of dorsiflexion when you walk or run or when you're doing your squats on leg day. During the squat movement, dorsiflexion draws our knee forwards over the back of our feet preventing our center of gravity from moving too far backwards. Without our dorsiflexes, like the extensor hallucis longus, we would constantly find ourselves tipping backwards every time we squat or tripping over everything when walking including ourselves.
It's important to clarify that the extensor hallucis longus is not the most important muscle for dorsiflexion of the ankle. It actually only helps other powerful dorsiflexors from the anterior compartment of the leg such as the tibialis anterior with this movement.
So there you have it, the functions of the extensor hallucis longus muscle.
Before saying our goodbyes, let's recap what we've learned in these past few minutes. We've seen that this muscle acts on three joints – the ankle together with the metatarsophalangeal and interphalangeal joints of the great toe. In terms of movements, the extensor hallucis longus is capable of producing hallux extension by moving the great toe upwards around the metatarsophalangeal and interphalangeal joints. In addition, it also contributes to dorsiflexion by helping other powerful muscles to move the foot towards its dorsum part around the ankle joint. Hallux extension is not as boring as it looks after all, is it?
I hope you enjoyed this tutorial about the functions of the extensor hallucis longus. See you soon and all the best!