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Functions and anatomy of the dorsal muscles of the foot shown with 3D model animation.
Toes! Wiggly toes. Too much toe action for you? Sorry, I was just trying to get you excited about the muscles of today’s tutorial. You see, today, we’re going to be looking at two small muscles in your foot, which help you lift your toes off the ground. Yes, I know. It’s not exactly the most mind-blowing movement, but every muscle has a story to tell. Stay with me now and find out more as we explore the functions of the dorsal muscles of the foot.
So, today, we’re going to be looking at the functions of two muscles. Firstly, the extensor hallucis brevis muscle which as its name suggests has something to do with the hallux or the big toe and the extensor digitorum brevis muscle which acts on the second to fourth digits of the foot.
Just one thing that I’d like you to note. Sometimes, these muscles are considered a single muscle, due to the fact that they often blend into one another. But for the sake of completeness, we’re going to consider them separately. So, let’s begin our study today by first reminding ourselves about the anatomy of each of these two muscles, beginning first with the extensor hallucis brevis muscle.
So as you can see in our spiffy 3D model here, the extensor hallucis brevis muscle has its origin or proximal attachment on the superolateral surface of the calcaneus bone close to the calcaneocuboid joint. And from here, the long slender body of the extensor hallucis brevis courses distomedially along the dorsum or the back of the foot, where it inserts into the base of the proximal phalanx of the great toe. Nice and straightforward.
Let’s turn our attention now to the extensor digitorum brevis muscle, whose anatomy is not unlike that which we saw with the extensor hallucis brevis. It, too, has its origin on the superolateral surface of the calcaneus bone of the foot, and from here the extensor digitorum brevis generally gives off three slips which course distally along the back of the foot to insert into the bases of the middle phalanges of the second through fourth digits or alternatively by attaching to the tendons of its brother, the extensor digitorum longus muscle, which you can see here.
I should add that this muscle is somewhat variable in its anatomy in that sometimes one or more of the muscular heads are absent, or alternatively, an additional head is present and this attaches to the fifth digit.
Now, when we consider the anatomy of any muscle, it’s important for us to identify the joints which they act upon since that’s where any movement will occur. In the case of the extensor hallucis brevis, we’re going to be focusing on just one joint – the metatarsophalangeal joint of the big toe – and this is where the first metatarsal bone articulates with the proximal phalanx of the big toe.
The extensor digitorum brevis – the metatarsophalangeal joints are also in question here – this time, those of the second through fourth digits. In addition, this muscle also acts upon the proximal interphalangeal joints of the same toes. This is the articulation between the proximal phalanx with the middle phalanx of each digit.
But, of course, no muscle is an island, and for a muscle to perform its functions, it needs to know what action you want to perform, how to do it, and when. This type of information is carried by nerves, and muscles are innervated by many of them. And in the case of both the extensor hallucis brevis and extensor digitorum brevis muscles, our nerve of interest here is the deep fibular nerve. And just a note, it’s useful to know the root values of the nerve associated with the muscle that we’re learning. So, in this case, the root values of the deep fibular nerve specifically its muscular branches to the dorsal muscles of the foot are L5 and S1.
So, now that we’ve learned the ins and outs of the extensor hallucis brevis and the extensor digitorum brevis muscles, it’s time for us now to turn our attention to their functions. And once again, we’re going to consider each muscle separately.
So, just as its name suggests, the primary function of the extensor hallucis brevis muscle is to assist in extension of the hallux at the metatarsophalangeal joint. And I say assist for the reason that this movement is primarily achieved by the big brother of this muscle, the extensor hallucis longus. So, the extensor hallucis brevis muscle serves to help with the support of this movement.
Looking at the movement again, we can see that extension of the big toe can occur from a flexed position returning the big toe back to their neutral position or further extension of the big toe which is sometimes referred to as hyperextension.
And turning our attention now to the extensor digitorum brevis muscle, its functions are quite similar to what we saw with the extensor hallucis brevis. So, you can probably guess that the primary function of this muscle is to assist extension of the second to fourth digits at the metatarsophalangeal joints of the same toes with some movements also occurring at the proximal interphalangeal joints also.
And just like the extensor hallucis brevis, the extensor digitorum brevis works to help or support the larger extensor digitorum longus muscle in achieving this movement.
Man, I don’t know how many times I’ve used the word extensor in this video, but there you have it. We’ve actually discussed all the functions of the extensor hallucis brevis and the extensor digitorum brevis muscles. Too easy!
Before I leave you, let me very quickly recap the functions of the two muscles that we met today.
So, we first looked at the extensor hallucis brevis which we learned is involved in extension of the hallux or the big toe at the metatarsophalangeal joint of the same digit. And then we looked at the extensor digitorum brevis, which works to assist in extension of the second to fourth toes occurring at the metatarsophalangeal and proximal interphalangeal joints of the same digits.
So that’s it! Done and tested! I hope you enjoyed watching this short video tutorial on the functions of the dorsal muscles of the foot as much as we did making it. Until next time, happy studying!