A medical device system for implantation in a hip joint, for providing at least one artificial hip joint surface for a patient. The medical system comprises an artificial caput femur surface (45) and an artificial acetabulum surface (65). The artificial acetabulum surface comprises a largest cross-sectional distance that is variable such that the partly bowl-shaped artificial acetabulum surface can be inserted through a hole in the pelvic bone, from the abdominal side of the pelvic bone, the hole having a diameter smaller than said largest cross-sectional distance； and a functional opening adapted to be directed towards the artificial caput femur surface, when implanted in the patient, the functional opening having a size adapted to be variable such that it is smaller than the largest diameter of the artificial caput femur surface, when implanted, such that the artificial acetabulum clasps the surface of the artificial caput femur surface.
