A medical device for implantation in a hip joint of a patient is provided. The medical device comprising a first piece being adapted to be fixated to the femoral bone and a second piece adapted to be fixated to the pelvic bone. The medical device further comprises a releasing which in a first state is adapted to hold said first piece attached to said second piece, and in a second state release said first piece from said second piece. The releasing member is adapted to change from said first state to said second state when a predetermined strain is placed on said releasing member by the connection with the first or second piece. The medical device further comprises a calibration member for calibrating the pre-determined strain required for said releasing member to change from said first state to said second state.