Hello, everyone! This is Joao from Kenhub, and welcome to another anatomy tutorial where, this time, I’m going to be talking about the lateral muscles of the sole of your foot.
Now, what I’m going to be doing is covering the different origins, insertions, innervation, and also functions associated to this group of muscles that you see on the right side, on this image on the right side, that are known as the lateral muscles of the sole of your foot.
Now, on your foot, you have what is called a lateral compartment, which is formed by the plantar fascia, which contains these three muscles. Now, their muscle bellies form the surface of the lateral sole of the foot, what is known to be as the ball of the little toe, so they’re in the same direction of your little toe.
So this is the lateral side of your foot, and this is the medial side, which is on the same side of your big toe.
Now, before I start talking about these muscles specifically, I would like to list them, and the muscles that are going to be covered here as the lateral muscles of the sole of the foot are the abductor digiti minimi, the flexor digiti minimi brevis, and the opponens digiti minimi. And keep in mind that this last muscle is not found in all humans.
And before describing all these three muscles, I would like to start off with the innervation of the lateral muscles of the sole of the foot.
Now, the brilliant part here is that you only need to remember that there is this nerve here, seen highlighted in green, that is responsible for innervating the lateral muscles of the sole of the foot, and this is the lateral plantar nerve.
We are going to start off with the first muscle now on our list, known as the abductor digiti minimi, and in terms of origin points, you need to remember that this muscle is going to originate from the calcaneal tuberosity, and you can clearly see here from this image.
So this is the calcaneal tuberosity serving as origin point for the abductor digiti minimi.
And another structure—this time, not a bony structure—but that will serve as also an origin point for this muscle specifically is the plantar aponeurosis.
In terms of the insertion point for the abductor digiti minimi, this muscle will insert at the base of the fifth proximal phalanx and also the fifth metatarsal bone. So you can clearly see here the fifth metatarsal bone and also the base of the fifth proximal phalanx serving as two insertion points for this muscle.
We are ready now to move on to the different functions associated to the abductor digiti minimi, and what you need to know and write down is that this muscle is going to be able to flex the little toe.
And as the name indicates, “abductor digiti minimi” (digiti minimi means “little toe”) it’s going to, then, abduct the little toe, as seen indicated here by this arrow.
So when you spread your little toe to the side, this is what we call abduction of the little toe. And this muscle is clearly involved in this movement.
Furthermore, it actively supports the longitudinal arch of the sole of your foot.
We’re going, now, to move on to the next muscle on the list, and this one is known as the flexor digiti minimi brevis.
And this muscle, in terms of origin points, is going to run from the base of the fifth metatarsal bone, as you can clearly see here, or you can see a little bit of the fifth metatarsal that is hidden behind the muscle. And the base of the fifth metatarsal bone is serving as origin and also the long plantar ligament, as you notice here, is serving as, also, an origin point for the flexor digiti minimi brevis.
Wow, what a long name. But we have to always mention it.
And hey, in anatomy, we always have to remember these long, long names, but we’re here to support you as much as we can.
We’re going to move on now and talk about the insertion point for the flexor digiti minimi brevis, and this muscle is going to, then, insert at the base of the fifth proximal phalanx, as you can also see here on this image. This is the fifth proximal phalanx, and the base found proximally is now serving as insertion point for the flexor digiti minimi brevis.
The next point to be made about this muscle is the functions that you associate to the flexor digiti minimi, and this image clearly shows one of the functions here. And it is the flexion of the little toe, and you can clearly see.
And based on the origin and insertion points, when this muscle contracts, it’s going to be able to cause flexion of your little toe.
Another function important here… or that we should highlight here is that it supports… it also supports the longitudinal arch of the sole of your foot.
Now, before I conclude this tutorial, I would like to use this image here of the sole of your foot, showing the different muscles that we find on this area of your body.
Now, one important thing to show here is that there are some muscles here, some groups that we have already covered, or all groups are covered here at Kenhub: the central group, the medial group, and this one that we’re covering on this tutorial, specifically, the lateral group.
Now, the point that I would like to make using this image—and before I do so, I’m going to remove here this muscle, the flexor digitorum brevis—the point to be made here is that when we compare the medial group to the lateral group, we can see that the medial group is clearly more developed than the lateral group.
And another point to make here before we finish this tutorial is that the lateral group is going to have little importance when it comes to the movements of the foot.