The Hip Joint

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This is a tutorial on the hip joint. The hip joint is this joint here between the head of the femur and the acetabulum of the pelvis. This joint is a ball-and-socket synovial joint and it’s a very stable joint unlike the shoulder joint, which is very mobile, but not so stable. This is the opposite.   It’s very stable and not quite as mobile as the glenohumeral joint of the shoulder.

There are several movements which occur at this joint. We’ve got abduction and adduction. We’ve got flexion and extension. We’ve also got medial rotation and lateral rotation. Flexion, extension, abduction and adduction can be combined movements to produce circumduction.   There’s several movements to this joint.

 

We’ll just take a look at the articular surfaces of this joint and then we’ll take a look at some of the ligaments and that sort of thing.

 

I’ll just remove the femur temporarily, so we can just take a look at the acetabulum. You can see the acetabulum here and it’s the circular depression in the pelvis. There are two parts to this. You’ve got an articular part and a non-articular part.

 

You can see that there’s a depression right in the center of the acetabulum and this is called the acetabular fossa. This part is non-articular.

 

Just surrounding it, you can see there’s this crescent shape surface. This is called the lunate surface. I’ll just zoom in a little bit further and I’ll draw that in for you. What I’m drawing on here is the lunate surface. This surrounds the acetabular fossa. This is the articular part of the acetabulum.   The acetabular fossa is this bit in the middle, which I’m just scribbling on.

 

You’ll notice that there’s a little gap between these two ends of the lunate surface. This is called the acetabular notch. The acetabular notch is inferior on the acetabulum.

 

We’ve got the two parts of the acetabulum. We’ve got the articular part, the lunate surface, which is crescent-shaped and surrounds the margins of the acetabulum and you’ve got the acetabular fossa, which is the non-articular bit depression at the center of the acetabulum.

 

The acetabular fossa is the point of attachment for the ligament of the head of the femur, which I’ll show you in a moment.

 

Surrounding the margins of the acetabulum, you’ve got a fibrocartilaginous collar. This is called the acetabular labrum. This deepens the acetabulum, so it stabilizes the joint further. As it crosses this notch here, the acetabular notch, it forms a ligament called the transverse acetabular ligament.

 

In the acetabulum, you’ve got the articular and non-articular parts. You’ve got the acetabular labrum surrounding it, which crosses the acetabular notch inferiorly to form the transverse acetabular ligament.

 

I’ve just switched over to a diagram to show you the ligamentum teres or the ligament to the head of the femur. This ligament attaches at one end to the acetabular fossa and it attaches on the head of the femur on a point called the fovea, which is the non-articular part of the femur.

 

This ligament is quite important to know about because it carries a branch of the obturator artery called the acetabular branch of the obturator artery. This provides a little bit of the blood supply to the head of the femur.

 

Here’s a femur that’s been isolated. You can see this little depression on the head of the femur.   That’s where the ligament of the head of the femur attaches and this is called the fovea and it’s the non-articular part of the head of the femur.

 

I’ll just give you a better view of the acetabular notch. I’ll just rotate the pelvis around and you can see this little notch here. That’s where the transverse acetabular ligament crosses.

 

Now that we’ve looked at the articular surfaces of the hip joint, we can now talk about the joint capsule and ligaments.   Here, we’re looking at the joint capsule of the hip.   We’ll just take a look at the attachments of this joint capsule.

 

You can see it attaches on the margins of the acetabulum. And then it attaches to the transverse ligament, which lies over the acetabular notch and it also blends with the border margin of the obturator foramen, which is this big hole here.

 

And then laterally, it attaches on this line here between the greater and lesser trochanter.   This is the intertrochanteric line. If I rotate the model around, you can see at the back its attachment.   It attaches just a bit proximal to the intertrochanteric crest.

 

That’s the attachments of the joint capsule. It’s really important to know the attachments of the joint capsule because the main blood supply to the head of the femur comes from vessels that travel underneath the capsule along the neck.

 

If you remember I talked about the blood supply that comes directly into the head via the ligamentum teres or the ligament to the head of the femur, but that’s not a big amount of blood supply. The main blood supply is through these vessels which comes underneath the joint capsule up the neck.

 

This is important because if a fracture of the neck of the femur is intracapsular, so within the boundaries of these attachments, then the blood supply to the head of the femur can be compromised and you can get avascular necrosis, which just means death of a tissue because of poor blood supply or disrupted blood supply.

 

If a fracture occurs outside the boundaries of this joint capsule, so extracapsular, then it’s unlikely that the blood supply will be compromised.

 

You’ve got three ligaments which reinforce this joint capsule. You’ve got the iliofemoral ligament, the pubofemoral ligament and the ischiofemoral ligament.

 

The iliofemoral ligament is this ligament here. This attaches just between the anterior inferior iliac spine and the margin of the acetabulum.   You can see the anterior inferior iliac spine here and the attachment of the iliofemoral ligament.

 

It’s got this kind of y-shape. I’ll just isolate it, so you can see this y-shape of the iliofemoral ligament and it attaches on this intertrochanteric line.

 

And then we’ve got the pubofemoral ligament. That’s this ligament here, which I’ve just isolated. This attaches on the iliopubic eminence and attaches onto the femur.

 

And if I rotate the model posteriorly, we can see this final ligament, the ischiofemoral ligament. This attaches at one end to the ischium and at the other, it attaches to the greater trochanter.   It’s this ligament here.

That’s the hip joint.