The HIP, or coxo-femoral joint, is one of the main joints in the human body. It is formed by two spherical bone extremities, one concave (the acetabulum), the other convex (the femur head), which move in all planes. The femur head is thus free to turn inside the acetabulum.
The two surfaces of the femur head and acetabulum are perfectly congruent and covered by cartilage, a structure that protects the bone and facilitates the sliding motion of the two articular elements. The femur head is not fully within the cavity of the acetabulum however. The extreme stability of the joint is also ensured by the acetabular labrum, which extends the contact surface of the femur head by enveloping its entire circumference.
The intracapsular ligament, at the top of the femur head, anchors the femur head to the bottom of the acetabulum, thus acting as a further guarantee of joint stability.
The whole of the femur head is enveloped by the articular capsule, a structure attaching to the acetabular lip and delimiting the articular space.
Around the articular capsule there are numerous ligaments providing stability, while a number of muscles enable movement of the joint.