Hip joint device and method

A medical device for implantation in a hip joint of a patient, wherein said 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, and wherein said medical device is adapted to receive a caput femur or a prosthetic caput femur having a spherical portion, wherein

• a) said medical device comprises at least one holding member for restraining said caput femur, or said prosthetic caput femur in said medical device,
• b) said at least one holding member is slidable in a direction more transversal to than parallel with a center axis of a collum femur, and wherein
• c) said medical device is adapted to release the caput femur or prosthetic caput femur from said medical device by sliding said at least one holding member away from the center axis of the collum femur when a predetermined strain is placed on said medical device by abnormal movement of the hip joint caused by the patient.