Hip joint

Hey everyone! This is Nicole from Kenhub, and in this tutorial, we're going to be looking at the hip joint, its articulations, movements, blood supply and innervation.

So, the hip joint is a ball and socket synovial joint forming the connection between the lower limb and the pelvic girdle and, as we can see in this image, we have the pelvis here and the right femur just here. And the hip joint is also multi-axial meaning that it rotates on more than one axis which allows for a wider range of movement. And, of course, the hip joint is designed for stability and weightbearing.

So as we can see in this image, the head of the femur articulates with the lunate surface of the acetabulum of the pelvis. The lunate surface is concave which is like the shape of a crescent moon as the name lunate suggests. And the hip joint can therefore also be referred to as the acetabulofemoral joint. Now, both the lunate surface of the acetabulum and the head of the femur are covered by hyaline cartilage with the exception of the fovea capitis femoris which we'll talk a little bit about later. And, of course, hyaline cartilage is a simple cartilage found on many articulating surfaces.

So, the acetabulum is the part of the pelvis where the ilium, ischium and pubis bones merge and as we've mentioned before, it's concave and almost entirely encompasses the head of the femur which of course contributes to the stability of the joint, and we've already mentioned the lunate surface of the acetabulum which is covered by hyaline cartilage. So as we can see in this image at the center of the acetabulum is a non-articulating surface which is known as the acetabular fossa just here, and this part of the acetabulum contains loose connective tissue, a mobile fat pad and is not covered by hyaline cartilage.

The acetabular labrum is the fibrocartilaginous collar or lip that surrounds the bony rim of the acetabulum and as we can see, it bridges across the acetabular notch just here as the transverse acetabular ligament. And the labrum of the acetabulum increases the stability of the hip joint by deepening the acetabulum and increasing the area of articulation with the head of the femur.

So as we can see in this image, the ball of the ball and socket hip joint is the rounded head of the femur which sits within the concavity of the acetabulum which is our socket of the joint. And the head of the femur is entirely covered by hyaline cartilage except for an area called the fovea capitis femoris which we have talked about briefly before. This is where the ligament of the head of the femur connects the femur at the fovea to the acetabular fossa, the transverse acetabular ligament, and the margins of the acetabular notch.

And now let's just point out some of these structures in this image. So, we have the fovea capitis sticking out here. This is, as we've mentioned, the ligament of the head of the femur. And then we have the acetabular fossa here, the transverse acetabular ligament running across here, and the acetabular notch margins which are just here.

So now we're going to move on to talk about the joint capsule which we can see in this image covering the head of the femur and the acetabulum. So, the joint capsule of the hip joint attaches to the acetabular labrum and the transverse acetabular ligament proximally which we can't see in this image but is underneath the fibrous capsule just here while attaching to the intertrochanteric line of the femur which is shown in green distally. And as it has to be, it is a strong fibrous capsule that can accommodate a wide range of movements and the capsule is strengthened and reinforced by the help of three ligaments.

Anteriorly and superiorly by the iliofemoral ligament which connects the anterior inferior iliac spine and the acetabular rim to the femoral intertrochanteric line, and the iliofemoral ligament is the strongest of the hip joint ligaments. Inferiorly and anteriorly, the pubofemoral ligament arises from the obturator crest and the superior ramus of the pubis and blends with the capsule and the medial part of the iliofemoral ligament. And posteriorly, the ischiofemoral ligament seen here from a posterior view connects the ischial part of the acetabular rim to the neck of the femur. And as we can see, the fibers from these three ligaments are arranged in a spiral fashion around the hip joint which helps stabilize the joint by pulling the head of the femur medially into the acetabulum. This reduces the amount of muscle energy required to maintain a standing position and it prevents the hyperextension of the hip as well as excessive abduction.

So now let's talk about the range of movements in the hip joint. So the range of hip movements in the hip joint include flexion – movement of the leg forward; extension – movement of the leg backward; abduction – movement of the leg laterally away from the midline of the body; adduction – movement of the leg medially towards the midline of the body; medial rotation – internal rotation of the thigh towards the midline of the body; lateral rotation – outward rotation of the thigh from the midline of the body; and circumduction – conical precise 360° movement of the leg.

And blood is supplied to the hip joint primarily by the medial and lateral circumflex femoral arteries – the medial shown on the left and the lateral shown on the right – and both of these arise from the deep femoral artery. And also by the artery to the head of the femur which runs within the ligament of the head of the femur which is shown in green and the artery to the head of the femur is a branch of the obturator artery.

And innervation of the hip joint comes anteriorly from the femoral nerve, inferiorly from an articular branch of the anterior division of the obturator nerve, posterosuperiorly from the superior gluteal nerve, and laterally from the articular branch of the sciatic nerve.

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