A medical device system for implantation in a hip joint of a human patient. The medical device system comprises an artificial caput femur (45, 607) adapted to replace at least the surface of at least one of the caput femur and the acetabulum. The artificial caput femur comprises a positioning through hole (910), and a positioning shaft (900) adapted to be stabilized by and placed in at least one of the femoral bone and the pelvic bone. The positioning through hole of the artificial caput femur is adapted to surround the positioning shaft, for positioning the artificial caput femur in a desired position in the hip joint. The positioning shaft is adapted to be placed in the positioning through hole of the artificial caput femur and in a positioning hole of an artificial acetabulum, for positioning the artificial caput femur and artificial acetabulum in relation to the at least one of the femoral bone and the pelvic bone and for aligning the artificial caput femur in relation to the artificial acetabulum.
