A medical device for implantation in a hip joint of a patient. The medical device comprises an inner and an outer surface, wherein a contacting portion of said inner surface is spherical and adapted to face a center of the hip joint when said medical device is implanted. The medical device is adapted to receive a caput femur or a prosthetic caput femur having a spherical portion. Said medical device comprises at least one extending portion adapted to clasp the caput femur, or prosthetic caput femur, for restraining said caput femur, or said prosthetic caput femur in said medical device. The extending portion comprises an elastic portion, and the medical device is adapted to release the caput femur or prosthetic caput femur from said medical device by deflecting said at least extending portion when a predetermined strain is placed on said medical device by abnormal movement of the hip joint caused by the patient.