The thighbone, femur and pelvis join to form the hip joint. The hip joint is a “ball and socket” joint. The “ball” is the head of the femur or thighbone, and the “socket” is the cup-shaped acetabulum of the pelvic bone. The joint surface is covered by a smooth articular surface that allows pain-free movement in the joint. The cartilage cushions the joint and allows the bones to move on each other smoothly.
The pelvis is a large, flattened, irregularly shaped bone, constricted in the center, and expanded above and below. It consists of three parts: the ilium, ischium and pubis. The acetabulum is situated on the outer surface of the bone and articulates with the head of the femur to form the hip joint.
The femur is the longest bone in the skeleton. It joins the pelvis (acetabulum) to form the hip joint.