Constrained mobile bearing hip assembly and method

An acetabular hip implant, comprising:

• an acetabular shell component configured to be implanted within an acetabulum of a patient, the acetabular shell having a first feature defined in its inner surface,
• a first insert secured to the acetabular shell component such that an outer surface of the first insert contacts the inner surface of the acetabular shell, the first insert having a second feature defined in its outer surface which contacts the first feature defined in the inner surface of the acetabular shell such that the first insert is (i) permitted to rotate relative to the acetabular shell component about a first axis and (ii) prevented from rotating relative to the acetabular shell component about a second axis and a third axis, the first insert having a third feature defined in its inner surface,
• a second insert secured to the first insert such that the outer surface of the second insert contacts the inner surface of the first insert, the second insert having a fourth feature defined in its outer surface that contacts the third feature defined in the inner surface of the first insert such that the second insert is (i) permitted to rotate relative to the first insert about the second axis and (ii) prevented from rotating relative to the first insert about the first axis and the third axis, the second insert having a fifth feature defined in its inner surface, and
• a femoral head extending along the third axis, from a first end configured to be secured to a femoral stem, to a second end, the femoral head being secured to the second insert such that the outer surface of the femoral head contacts the inner surface of the second insert, the femoral head having a sixth feature positioned at the second end, opposite the femoral stem when the femoral head is secured to the femoral stem, the sixth feature being defined in its outer surface which contacts the fifth feature defined in the inner surface of the second insert such that the femoral head is (i) permitted to rotate relative to the second insert about the third axis and (ii) prevented from rotating relative to the second insert about the first axis and the second axis;
• wherein the sixth feature is annular, symmetrical about the third axis, and offset from a diameter of the femoral head, and
• wherein interaction between the first and second features, between the third and fourth features, and between the fifth and sixth features mechanically constrains the acetabular hip implant to prevent dislocation of the femoral head during rotation.