A medical device for implantation in a hip joint of a patient is provided. The medical device comprises a prosthetic caput femur having least partially spherical portion and a releasing member. The releasing member is adapted to, in a first state, restrain the at least partially spherical portion in an acetabulum or a prosthetic acetabulum and, in a second state, to release the at least partially spherical portion from the acetabulum or the prosthetic acetabulum. The releasing member is further adapted to change from the first state to the second state and from the second state to the first state when a strain, exceeding a predetermined threshold, is exerted on the hip joint.
