Hip joint device and method

A medical device for implantation in a hip joint of a patient, said medical device comprising:

• a. a first piece, wherein
• i. said first piece is adapted to be fixated to the pelvic bone, and
• ii. said first piece comprises a convex contacting surface adapted to be partially placed inside a concave contacting surface,
• b. a second piece, wherein
• i. said second piece is adapted to be fixated to the femoral bone, and
• ii. said second piece comprises a concave contacting surface adapted to partially surround said convex contacting surface of said first piece, when implanted, and
• c. a releasing member adapted to, in a first state hold said first piece attached to said second piece, and in a second state release said first piece from said second piece, and wherein said releasing member is adapted to change from said first state to said second state when a pre-determined strain is placed on said releasing member.