The hip joint is one of the most important joints in the human body. It plays a critical role in daily activities such as weight lifting, walking, running, jumping and retaining balance. The hip joint is one of most flexible joints with a great range of motion in the human body. It bears the force of the strong muscles of the hip and leg. Anatomically, the hip joint is made up of two bones: the pelvis and the femur (the thighbone). It is the largest ball-and-socket synovial joint in the human body. The ball is the femoral head, and the socket is a concave depression in the lower side of the pelvis called the acetabulum. The femoral head fits into the acetabulum to form the hip joint with flexibility for motion.
The round head of the femur rotates and glides within the acetabulum. The depth of the acetabulum is further increased by a fibro-cartilaginous labrum attached to the acetabulum. The neck of the femur connects the femoral head with the shaft of the femur. The capsular ligament of the hip joint attaches to the posterior part of the femoral neck. At the top of the femur, next to the femoral neck, there is another bump on the outside of the hip called the greater trochanter, to which muscles attach. The greater trochanter serves as the site of attachment for the abductor muscles. The stability of the hip is increased by the strong ligaments that encircle the hip. The muscles of the thigh and lower back work together keep the hip stable, aligned and moving. A slippery tissue called articular cartilage covers the surface of the ball and socket. Cartilage helps prevent friction between the femoral head and the acetabulum, and hip pain can occur if cartilage begins to wear down or is damaged.