Video: Hip bone

Shakira once said that our hips don't lie. You know, she may have been alluding to a fundamental anatomical truth. In your awkward adolescence, as you become more 'hip', there's also a trio of bones that comes together to form your actual hip bone. That means as you grow and your hip bones fuse, you elevate one's 'hip' quotient to a whole new level. And let's be real. Only a total hipster would appreciate the gravity of that wordplay.

In today's tutorial, we're going to look at the hip bone.

Before we begin, it's important that we first define the bony pelvis. Now the bony pelvis, which we can see here from an anterior perspective and highlighted in green, is formed posteriorly by the sacrum and the coccyx and laterally and anteriorly by a pair of hip bones, or pelvic bones.

So, as you can see here, you have a left hip bone and a right hip bone and each hip is a trio – three parts fused that fuse together towards the end of puberty. These parts include the ilium, which is the largest and most superior of the three bones; the ischium, which is located inferiorly; and the pubis, or the pubic bone, which forms the most anterior portion of the hip bone.

We're going to discuss these three components of the hip bone in more detail. But before we do that, let's first talk about a structure where they all meet which is known as the acetabulum.

In order to view the acetabulum more clearly, we've changed our perspective slightly. What we're looking at now is the left hip bone from a lateral perspective – so here's the ilium superiorly, the ischium posteriorly, and the pubis anteriorly. The acetabulum, as I mentioned, is a cavity formed by the synostosis, or fusion, of these three bones.

The hip joint is a ball-and-socket joint. This means that it is a joint with a rounded bone, referred to as a ball, moving within a depression of another bone, called the socket. Well, the acetabulum forms the socket component of the hip joint while the ball component is formed by the head of the femur.

Now moving on, I want to talk about a few structures associated with the acetabulum, and the first one is this moon-shaped structure that is conveniently known as the lunate surface. This curved articular surface surrounds the acetabulum and articulates with the head of the femur. Since it is an articular surface, it is covered by articular cartilage.

The next structure we're going to look at is the margin of the acetabulum. As you can see, this is bordering the acetabulum and is interrupted here by this notch, which is known as the acetabular notch.

The last structure of the acetabulum we'll look at today is the acetabular labrum, or the acetabular lip. This structure can be confused with the margin of the acetabulum, however, they're not the same thing. The acetabular labrum is a fibrocartilaginous collar on the rim of the acetabulum, as you can see here, that is surrounding the margin of the acetabulum.

So we've been talking about these three bones that fuse during puberty to make us more 'hip'. Let's take a look at these in more detail starting with the ilium.

The ilium itself is divided into two main parts – the wing, or ala, and the body. The wing is this flattened portion you see here and the body is the central part of the ilium that you see here, contributing to the formation of the acetabulum.

Now we'll discuss some bony landmarks associated with the ilium. The first one we'll talk about is the arcuate line. We've changed perspective again so let's orientate ourselves. We're now looking at the left hip bone from a medial perspective. We can see here that it is a smooth rounded border on the internal surface of the ilium and that it marks the transition between the body and the wing of the ilium. It also forms a part of the border of the pelvic inlet.

Another structure we can see from the medial perspective is the iliac tuberosity. The iliac tuberosity is a roughened, elevated area found posterior to the iliac fossa and serves as an attachment point for the sacroiliac ligaments. Inferior to the iliac tuberosity, we can see the auricular surface. As the name indicates, this is an ear-shaped surface and it articulates with the sacrum. This surface is covered by fibrocartilage.

Contributing to most of the internal surface of the wing of the ilium is the iliac fossa. As you can see, it is a large, smooth, concave surface found on the medial aspect of the hip bone. The iliac fossa is bordered superiorly by the iliac crest and inferiorly by the arcuate line.

If we flip our hip bone over to view its lateral surface, we can see some more bony structures. The first one we'll look at is the gluteal fossa or the gluteal surface. This fossa contributes towards most of the external surface of the wing of the ilium and provides various points of attachment for the gluteal muscles.

There are three curved ridges on this surface known as the anterior, posterior, and inferior gluteal lines. The anterior gluteal line, as we can see, travels obliquely along the gluteal surface from the tubercle of the iliac crest towards the greater sciatic notch. The posterior gluteal line descends from the external lip of the crest and ends anterior to the posterior inferior iliac spine. Lastly, the inferior gluteal line, as we can see, runs superior to the acetabular margin.

Next, we're going to talk about the iliac crest which, as I previously mentioned, forms the superior border of the iliac fossa and the wing of the ilium. The iliac crest extends from the anterior superior iliac spine here to the posterior superior iliac spine here. This crest serves as an attachment point for a large muscle of the body known as the latissimus dorsi.

Lastly, we're going to look at the spines of the ilium. The ilium has four different spines, and the first one we're going to talk about is one I already mentioned – the anterior superior iliac spine. As I said earlier, the anterior superior iliac spine is a bony projection that marks the anterior limit of the iliac crest and it is the origin of the sartorius muscle and inguinal ligaments.

Now we have the anterior inferior iliac spine which is a bony process found at the anterior margin of the ilium, inferior to the anterior superior iliac spine. This spine serves as the origin of the rectus femoris muscle.

The next spine is known as the posterior superior iliac spine which, as we already know, marks the posterior limit of the iliac crest. It's shorter than its anterior counterpart and serves as the attachment points for the oblique portion of the posterior sacroiliac ligaments and multifidus.

Let's move on to the last spine of the ilium known as the posterior inferior iliac spine. It is found on the superior edge of this really important structure here known as the greater sciatic notch.

So that's us finished with the ilium. Let's move on now to talk about another bone that contributes to the hip bone, the pubis.

The pubis is divided into three main parts – the body, the superior ramus, and the inferior ramus. The body is the wide, medial, and flat area we can see here which unites with its counterpart at the pubic symphysis. The superior ramus is this portion right here that is located just above the obturator foramen. The inferior ramus lies here between the pubic symphysis and the ramus of the ischium.

Again, the pubis possesses several bony landmarks and we're going to talk about the ones we can see from a medial perspective, starting with the iliopubic eminence. The iliopubic eminence is a flat prominence located at the proximal portion of the pubis. It marks the point of union between the ilium and the pubis.

Another structure found on the medial surface of the pubis is the symphyseal surface. This surface unites with its counterpart through a midline cartilaginous joint called the pubic symphysis, which you can now see highlighted from an anterior perspective.

Next, we'll have a look at the structure we can now see highlighted in green, which is the pubic tubercle. We can see that it is located on the anterior aspect of the body of the pubis, just lateral to the symphyseal surface. The pubic tubercle serves as an attachment point for the inguinal ligament.

Let's keep looking at the pubis from an anterior perspective while we talk about the next two structures.

The first one we'll talk about is the obturator crest. The obturator crest extends from the pubic tubercle here to the acetabulum here. It provides a point of origin for the pubofemoral ligament. Inferior to the obturator crest, we find the obturator foramen, which is the large opening you can see here between the pubis and ischium. The obturator nerve, artery, and vein pass through this foramen to enter the medial compartment of the thigh.

Now that we've covered the bony elements of the pubis, it's time for us to move on to the third and final bone of the hip bone, which is the ischium.

The ischium is divided into two main parts – the body and the ramus. The body is this portion right here located just behind the obturator foramen, and the ramus of the ischium is found here, just below the obturator foramen.

Let's look at the ramus of the ischium in a bit more detail. Here, we're looking at it from a medial perspective. We can see that the ramus of the ischium fuses with the inferior ramus of the pubis. So this is a meeting point between the ischium and the pubis.

If we change our view to a posterior perspective, we can see another key structure of the ischium which is the ischial spine. The ischial spine is a bony prominence found between the greater sciatic notch and the lesser sciatic notch. It serves as an attachment point for some important muscles, such as the coccygeus muscle.

Let's move on to talk about the greater sciatic notch in more detail.

This notch lies between the posterior inferior iliac spine here and the ischial spine here that we just talked about. When we add this ligament here, the sacrospinous ligament, this notch becomes what is known as the greater sciatic foramen.

So here we have the greater sciatic foramen. We can see the sacrospinous ligament here, hiding behind the sacrotuberous ligament. Several important structures pass through this foramen including the piriformis muscle and the sciatic nerve.

We mentioned another notch earlier, the lesser sciatic notch. This notch lies between the ischial spine here and the ischial tuberosity. When we add this ligament here, the sacrotuberous ligament, this notch becomes what is known as the lesser sciatic foramen. The lesser sciatic foramen has many important structures passing through it including the obturator internus muscle, the nerve that supplies this muscle, the internal pudendal vessels, and the pudendal nerve.

The last structure of the ischium we'll talk about today is the ischial tuberosity. Its function is to bear the weight of the body in a seated position, therefore, we can also call it the sitting bone.

Before we bring our tutorial to a close, let's quickly summarize what we learned today.

First, we looked at the hip bone and its bony landmarks. We saw that each hip bone comprises of three parts that fuse together towards the end of puberty. These include the ilium, the ischium, and the pubis. As these elements merge, they create a robust structure, laying the groundwork for fluid movement and stability. And in the immortal words of Shakira, "Hips don't lie," echoing the undeniable truth found in the concordance and harmony of these three bones.