A method for fixating an artificial convex caput femur surface to the pelvic bone of a patient, the method comprising the steps of: exposing the acetabulum surface, creating a hole or recess in the pelvic bone from the acetabulum side of the pelvic bone, providing the artificial convex caput femur, comprising an elongated member to the hip joint, inserting said elongated member in said hole, and performing an action on the acetabulum side of the pelvic bone such that the elongated member is structurally changed on the abdominal side of the pelvic bone or inside the pelvic bone.