Video: Hyoid bone
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Bones, bones, bones, bones. You know how the song goes. The hip bone is connected to the back bone. The back bone is connected to the neck bone – or something like that. Every bone in the human ske... Read more
Bones, bones, bones, bones. You know how the song goes. The hip bone is connected to the back bone. The back bone is connected to the neck bone – or something like that. Every bone in the human skeleton is connected to another bone, right? Well, actually, in the human skeleton, there's one bone that does not articulate with any other bones. Do you know what that is? That's right – it's the hyoid bone.
Before we get started, here's a quick overview of what we'll look at today. First, we'll look at the hyoid bone as a whole and where it sits in the body. Next, we'll look at its bony features, the main parts of the bone that are significant. We'll follow up by looking at other structures in the area beginning with adjacent cartilages and then moving on to just a few membranes and ligaments that are relevant to the hyoid bone itself. Lastly, we'll identify muscles that insert or originate on the hyoid. Are you ready? Let's get to it.
First up, the hyoid bone itself. In this image, we're looking at a lateral right view of the hyoid bone in its in-situ position. The hyoid is an isolated U-shaped bone in the anterior neck at the level of C3, which is around about here, and sits between the mandible over here and the thyroid cartilage which is this little bump covered by muscle here. In this pop-out, we're looking at the isolated hyoid bone from an anterior view.
Fun fact: The word hyoid comes from the Greek word hyoeides which means “shaped like the letter upsilon”. Upsilon is the twentieth letter of the Greek alphabet and is equivalent to our letter U, and looking at the hyoid bone in isolation, I think we can make the connection. I bet you didn't know you would be learning how to spell Greek in your hyoid tutorial, did you?
Let's go back to our lateral image of the bone. We can see in this image that the lateral parts of the hyoid bone travel deeper into the neck. The hyoid provides an attachment point for several groups of muscles including the strap muscles of the neck and the anterior part of the oropharynx and acts as an inferior anchoring point for muscles of the tongue.
Now we're looking at the hyoid bone from an anterior view in position in the neck. This bone also helps to keep the airway open.
We can now start looking at the different parts of the hyoid bone itself. The hyoid bone is made up of a body, two greater horns, and two lesser horns. The main part of the bone is called the body of the hyoid. The body is the middle, slightly thicker main portion of the bone we can see highlighted in this image. It's somewhat irregular in shape, but has a roughly posterosuperior concave form, meaning that it curves backwards and upwards. It acts as an attachment site for many muscles and membranes.
The main lateral extensions from the body are known as the greater horns or greater cornua of the hyoid bone. The horns project posterosuperiorly from the lateral sides of the body giving the hyoid its U-shape. In this image on the right, we can see the right greater horn projecting posteriorly into the neck.
In younger folk, the greater horns are often not completely fused to the body of the hyoid bone, but rather attached by a fibrocartilage. In people who are a little older in their years, this fibrocartilage ossifies uniting the greater horn with the body of the hyoid bone. The tips, or the apices of the greater horns, often remain cartilaginous until at least 30 years of age.
The final components of the hyoid bone are the two lesser horns, now highlighted in green. We can see these from an anterior view projecting posterosuperiorly from the body at its junction with the greater horns. The lesser horns of the hyoid bone are cartilaginous until at least puberty; however, in some adults, the lesser horns may not ever become ossified and remain partly or totally cartilaginous.
And that's it for the main structures of the hyoid bone. Pretty straightforward, hey? Let's have a look at some other adjacent structures in the area starting with the structures made of cartilage.
Inferior to the hyoid bone is the thyroid cartilage, which we can now see highlighted in green. It's the largest of the cartilages in this region. This cartilage is a major component of the larynx forming the laryngeal prominence. Also, part of the larynx is the cricoid cartilage. This cartilage is inferior to the thyroid cartilage as we can see in this nicely popped-out image. The cricoid cartilage is the only laryngeal cartilage that is a complete ring. Though you can't see it in this image, the cricoid is shaped like a signet ring with the flat signet part facing posteriorly, like this image. In fact, you could slip the cricoid cartilage on as jewelry as it fits the average finger.
Moving inferior still, we next come across the superior part of the trachea, which is, of course, the tube through which we breathe air and we can see its cartilage highlighted in green now. This will continue inferiorly and bifurcate into the two main bronchi. If we swap directions and look superior to the hyoid, we can see part of another cartilage projecting superiorly. This is the tip of the epiglottis, which is the cartilaginous structure that covers the glottis when swallowing.
And that wraps up the cartilaginous structures. We’ll now look at a membrane and a couple of ligaments in the area.
Attached to the inferior border of the hyoid bone is the structure we can now see highlighted in green. This membrane attaches the hyoid bone to the thyroid cartilage, so is appropriately named the thyrohyoid membrane. Now on the inferior aspect of the thyroid cartilage is a ligament that runs inferiorly to the cricoid cartilage. As it's in the midline, it's called the median cricothyroid ligament.
Let's go back now to our lateral image of some of the structures of the neck. In this image, we'll find a ligament that helps to suspend the hyoid bone within the neck. This is the stylohyoid ligament, drawn in a green highlight along the anterior aspect of the stylohyoid muscle, again, nicely named for its attachment points. It runs from the styloid process of the temporal bone to the lesser horn of the hyoid bone. As you can see, the stylohyoid ligament runs along the stylohyoid muscle and has the same attachments.
And now onto the last section of the structures. Let's now discover several muscles that originate or insert onto the hyoid bone.
The group superior to the hyoid bone are called the suprahyoid muscles.
The first muscle that we’ll identify is the one now highlighted in green. This is the mylohyoid. Let's zoom in a little so we can see the muscle a bit better. This muscle forms the floor of the oral cavity running from the mylohyoid line of the mandible to the body of the hyoid. The mylohyoid elevates the floor of the mouth, and by doing so, can elevate the hyoid bone itself.
If we remove the mylohyoid, deep to it we’ll find the geniohyoid. This muscle is more narrow, but has a similar trajectory to the mylohyoid originating from the genial tubercles on the internal surface of the mandible, which is where we get the stem genio- from and inserting onto the body of the hyoid. The geniohyoid elevates the hyoid and pulls it anteriorly.
The best way to see this next muscle is from a lateral view, so let's go back to one of our original views of this area, and here we can see the muscle originating from the greater horn of the hyoid. If we remove the mylohyoid, we'd be able to see this attachment continue on to the anterior part of the body of the hyoid as well. As its name suggests, the hyoglossus muscle fibers insert into the side of the tongue. The action of this muscle then is to depress the tongue.
The final suprahyoid muscles we'll look at today is called the stylohyoid. Do you have any idea where this one originates? Yep. Like the stylohyoid ligament, it arises from the styloid process of the temporal bone. It's also nicely visible from a lateral view as it travels anteriorly and inferiorly to insert on the body of the hyoid at its junction with the greater horn. This muscle elevates and pulls the hyoid posteriorly.
The final group of muscles we'll look at are those that are inferior to the hyoid bone. Appropriately, they are called the infrahyoid muscles, or also the strap muscles of the neck. The muscle highlighted now in green is called the thyrohyoid, named after its attachment points. The thyrohyoid originates at the oblique line of the lamina of thyroid cartilage, travelling vertically to insert at the body of the hyoid and its greater horn. This muscle depresses the hyoid bone.
Superficial to the thyrohyoid is a longer muscle called the sternohyoid. As its name suggests, it is attached to the sternum and the hyoid. More specifically, it originates at the manubrium of the sternum and the medial end of the clavicle, and inserts at the inferior border of the body of the hyoid bone. Similar to the thyrohyoid, the sternohyoid depresses the hyoid bone after swallowing.
Last, but not least, is this pair of oblique running muscles. This muscle is divided into two parts, a superior and inferior belly. The superior belly originates at the intermediate tendon and inserts onto the body of the hyoid, while the inferior belly originates at the superior border of the scapular near the suprascapular notch, and inserts onto the intermediate tendon. This muscle acts to depress the hyoid as well as fixing it.
Hooray! We're now done with the hyoid bone and its associated structures. So, what kind of issues may arise with this floating bone? Anything you can think of?
Well, funnily enough, although it doesn't articulate with any other bones, the hyoid is still prone to fracture. I know pretty weird, right? Imagine this bone isolated in the neck with so many muscles attaching to it, do you think you know what would happen? The hyoid bone would probably drop inferiorly onto the thyroid cartilage. The muscles that usually act to elevate the hyoid would have a hard time doing so. Ultimately, this would really hinder swallowing and could block the airway. But I know what you're wondering. You're wondering how on earth hyoids get fractured in the first place? Well, it's pretty morbid, but fractured hyoids are often caused by manual strangulation. I guess it's safe we’re leaving combat techniques to the professionals after all.
And now you're an expert on the hyoid bone. Before I let you go though, let's have a quick review of what we looked at today.
We started by looking at the hyoid bone as a whole and isolated bone in the anterior neck. We then identified its bony components – the body in the middle of the bone, the two greater horns laterally, and the two lesser horns projecting from the superior aspect of the body. Next, we looked at the cartilaginous structures nearby. First up, just inferior to the hyoid is the thyroid cartilage – a large component of the larynx. Inferior to the thyroid cartilage is the cricoid cartilage – the only cartilage in this area that is a complete ring. Moving inferior again, we saw the superior tracheal rings of the airway, and finally, we saw the epiglottis, showing at the superior aspect of the hyoid.
We then moved on to a membrane and two ligaments. Firstly, the thyrohyoid membrane which runs between the hyoid bone and the thyroid cartilage. More inferiorly and right in the midline is the median cricothyroid ligament. Suspending the hyoid bone is the stylohyoid ligament, better seen from a lateral view, and the final structure we identified in this specific image was the cricothyroid muscle which acts to tilt the thyroid cartilage anteriorly.
The suprahyoid muscles are muscles superior to the hyoid that insert onto it. The first one we identified was the mylohyoid. This muscle makes up the floor of the oral cavity. Deep to the mylohyoid, we found the geniohyoid, another elevator of the hyoid bone. More laterally is the hyoglossus, inserting into and depressing the tongue. Lastly, for this group, was the stylohyoid coming from the styloid process.
The last group of muscles were the infrahyoid muscles – muscles inferior to the hyoid bone. These are also called the strap muscles. First up was the thyrohyoid inserting inferiorly on the thyroid cartilage, superficial to that is the sternohyoid which depresses the hyoid bone, and finally, we identified the omohyoid – the pair of muscles that travel from the hyoid bone to the superior border of the scapula and depress the hyoid.
The last thing that we looked at is a hyoid bone fracture and how it can make swallowing really difficult.
And that brings us to the end of our tutorial. I hope you enjoyed it. Happy studying!