The hip joint (or coxo-femoral) is a typical enarthrosis (mobile joint – diarthrosis -, the articular surfaces of which consist of a spherical or hemispherical shape and a concavity which is in turn spherical) which joins the femur to the hip bone. The hip bone concurs with an almost hemispherical articular cavity, the acetabulum , Human Body Joints. and the femur with the femoral head which represents about 2/3 of a full sphere of 4 or 5 cm in diameter.