Anatomy of the hip joint

If you have ever wanted to know about the new ‘hip joint’ in town, look no further than the hip joint!

The hip joint is a large, strong joint connecting the pelvis to the lower limb. Let's take a closer look!

The hip joint is a synovial ball and socket joint, where the head of the femur forms approximately two thirds of a sphere, and it articulates with the cup-like acetabulum of the hip bone.

The femoral head is not entirely round, as it has depression on top of it which is called the fovea for the ligament of the head of the femur.

Except for the fovea, the femoral head is also covered entirely in articular cartilage which facilitates smooth movement and prevents bone erosion as it slides within the acetabulum.

The acetabulum, on the other hand, is a bowl like structure on the lateral aspect of the hip bone, and you might remember it is formed by the fusion of the ilium, ischium, and pubis.

The acetabulum is surrounded on the outside by a margin that’s incomplete inferiorly, where the acetabular notch is situated; this makes it look like a bowl with a broken rim.

On the outside of the acetabulum margin, there’s the acetabular labrum, where labrum is a fancy word for lip, which continues over the acetabular notch with the transverse acetabular ligament.

The labrum increases the surface area of the acetabulum to allow more than half of the femoral head to fit within the acetabulum for stability.

There’s also a rough depression in the floor of the acetabulum - the acetabular fossa, right above the notch.

These two structures, the acetabular notch and fossa, are surrounded by the thick and smooth lunate surface, the articular surface on which the head of the femur slides.

Just like most joints, the hip joint is enclosed within a strong joint capsule formed by an external fibrous layer, called the fibrous capsule, and an internal layer, called the synovial membrane.

The fibrous layer attaches proximally to the acetabulum peripheral to the acetabular margin, as well as to the transverse acetabular ligament.