The hip joint is a joint formed by the articulation of the femur, the long bone in the leg, with the pelvis. This joint serves a number of functions in the human body and it is one of the strongest and most durable joints. The hip is designed to bear considerable stress and pressure. The hip is also one of the areas of the human body which exhibits sexual dimorphism, with the hips of men and women being designed slightly differently as a result of the need to accommodate pregnancy and childbirth for women.
This joint is also known as the coxa or the acetabulofemoral joint. It is a ball and socket joint, with the head of the femur being inserted into a socket formed by the bones of the pelvis. In adults, the bones of the pelvis have completely fused, adding stability to the joint, while in children, the fusing of the pelvis is not yet complete. In another example of differences between men and women, in women, the cartilage which connects the bones in the pelvis is designed to soften during pregnancy to allow the bones to pull apart slightly, which destabilizes the hip joint and accounts for the distinctive gait women acquire during pregnancy.
The bones in the hip joint are covered in a layer of hyaline cartilage, also known as articular cartilage. This cartilage is smooth and very durable, designed to move without friction and to hold up under compression, stress, and pressure. The bones of the joint are further stabilized with ligaments and muscles which hold the bones in place and allow the hip a full range of movement.
One of the primary functions of the hip joint is to stabilize the body. The human body has needed to develop considerable adaptations in order to walk upright, and the hip joint is one of the most critical of these adaptations, stabilizing the body and distributing the weight of the upper body to the legs evenly. The joint provides stability when someone is stationary or walking, which is one reason why it needs a network of ligaments for support.
The hip joint also, of course, provides a range of motion for the leg. The ball and socket design allows the femur to move in a variety of directions, with some people such as dancers and yoga practitioners developing even more range of motion. This range of movement allows people to walk, run, and engage in a variety of other activities with the legs.