An acetabular hip implant, comprising: an acetabular shell component configured to be implanted within an acetabulum of a patient, a first insert secured to the acetabular shell component 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 first flat 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 second flat defined in its outer surface which contacts the first flat 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 third flat defined in its inner surface, and a femoral head configured to be secured to a femoral stem, 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 fourth flat defined in its outer surface which contacts the third flat 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 and characterised in that the acetabular component comprises a protrusion received into a recess in the first insert to allow rotation about the first axis and prevent rotation about the second or third axis. an acetabular shell component configured to be implanted within an acetabulum of a patient, a first insert secured to the acetabular shell component 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 first flat defined in its inner surface, (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 first flat 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 second flat defined in its outer surface which contacts the first flat 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 third flat defined in its inner surface, and a femoral head configured to be secured to a femoral stem, 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 fourth flat defined in its outer surface which contacts the third flat 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 and characterised in that the acetabular component comprises a protrusion received into a recess in the first insert to allow rotation about the first axis and prevent rotation about the second or third axis.