Hello everyone! This is Joao from Kenhub. Welcome to another tutorial. This time, I’m going to be covering the hypothenar muscles.
Now, keep in mind that, on this tutorial specifically, I’m going to be covering the origins, the insertions, and also the innervation of this group of muscles. Later on, I’m going to be focusing on the functions on a separate tutorial, but for now, this tutorial will be important for this training unit specifically.
Now, without further ado, let’s start with the tutorial talking about the muscles, and you see here on your left, an image of your hand on the palmar view if you were to strip your skin and also fat and be left with bones, ligaments, and of course, the muscles of the hands. Now, where to find the hypothenar muscles, this group right here. So this is where you’re supposed to find the hypothenar muscles, and this is on the ulnar side of your hand, more specifically, on your little finger side. So keep in mind, and also, as you can see here, this is a group of four short muscles. So let me highlight this that there are four hypothenar muscles that we’re going to be covering on this tutorial.
Before we do so, I also want to show you here an image of a hand where you can specifically find this group of muscles. If you were to do this position as well, you can clearly see here a prominence. So these muscles contracted, you can see here that this is forming what is called a hypothenar eminence. And this hypothenar eminence is where you can exactly find this group of muscles.
Now, let’s list them. And they have really interesting names, so keep... or bear with me as I list them because they’re quite funny, I would say. The first name is abductor digiti minimi, the second one is the flexor digiti minimi, and the third one, the opponens digiti minimi, and the last one that we’re going to be covering is the palmaris brevis.
So let’s start with the very first muscle. This is the abductor digiti minimi. And as you can see here, it is located at the border of the palm of your hand, and it clearly defines the medial or also known as the ulnar border of the palm of the hand. Now, in terms of origins, there is one origin that you need to know where this bone is starting, let’s say, and you can clearly see here on this image is the pisiform bone. And it goes all the way to insert here in two places that you need to remember, the proximal phalanx of the fifth finger and also the dorsal aponeurosis of the fifth finger.
Now, let’s move on to the second muscle of the list. This is the flexor digiti minimi muscle. And it is a very small muscle, and sometimes even completely missing. So as you can see here, it’s indeed a very small muscle. Now, in terms of the origins, you have to remember two, very important, two origin surfaces. And the first one is the flexor retinaculum, and the second one is the hook of the hamate bone. Now, in terms of its insertions, you need to know one. So distally, as you can see here, distally, it’s going to insert on the base of the proximal phalanx of the fifth finger, of the little finger.
Now, moving on to the third muscle of our list, this is the opponens digiti minimi muscle. And the opponens digiti minimi is the strongest and also the deepest of all hypothenar muscles. And in terms of its origins, there are two that you also have to remember, the same ones that you will see or that you saw on the flexor digiti minimi—so the flexor retinaculum and also the hook of the hamate bone. Now, in terms of insertions, you need to remember one. It inserts more proximally than the flexor digiti minimi muscle at the ulnar surface of the fifth metacarpal bone.
Now, let’s move on to the last muscle of our list, the palmaris brevis. Now, one thing that I want to add here, very important thing, is that even though this muscle is lying quite superficially, as you can see here—it’s above the groove that we’re talking about, the hypothenar muscles—it cannot be distinguished through palpation due to the fact that, as you can also see here, it is quite, quite thin muscle.
Now, the palmaris brevis also differs from the other three muscles in many ways, which is why it is often not considered as one of the hypothenar muscles. But I wanted to include here on this list since it is found on the same location, and some… some schools included it in the same list. But if you feel that this is not the list to go, feel free to exclude the palmaris brevis, but either way, we’re going to briefly talk about it.
Now, very first thing I want to talk about the palmaris brevis is its origin. Now, there are two origin points that we need to highlight. The first one is the flexor retinaculum and the second one, the palmer aponeurosis. In terms of the insertion for this muscle, the palmaris brevis, it’s going to go towards the skin to insert on a structure known as the palmer aponeurosis. And you can see it here on this image clearly. This is the palmer aponeurosis which is serving as insertion point for the palmaris brevis. You can also see that this is a characteristic of this muscle that it has a rectangular shape.
Now, let’s move on to the very last topic of this tutorial, the innervation of the hypothenar muscles. Now, I decided to leave this topic for last because all you have to know is that the hypothenar muscles are going to be innervated by one nerve, or they’re going to be supplied by one nerve, and this is the ulnar nerve from C8 to TH1, which courses along the flexor carpi ulnaris from the forearm to the wrist. And you can see here, highlighted in green, on this image to your right.
Now, one important thing to mention about the ulnar nerve is that it will divide into two branches once it passes the carpal bones: the superficial branch that you can see here highlighted in green—so this branch that is mixed here with all these vessels, and here, the hypothenar muscles that we’re looking at—and the deep branch of the ulnar nerve, which you can also see here branching off the ulnar nerve and this is the deep branch of the ulnar nerve. Now, important to also highlight here is that while the deep branch courses towards the metacarpus along with the ulnar artery and supplies the muscles of the hand, including the hypothenar muscles, the superficial branch travels distally underneath the palmaris brevis.