The original cup design (Fig. 3) was unchanged up until 1988, though metal backing was introduced, largely on theoretical grounds57, in 1984. The eccentric design of the original cup was subsequently shown to be unsound58 and changed to a more conventional concentric design (though with retention of the lateral skirt but  substitution of the original ‘wrap around’ skirt (Fig.3) by one that was tangential to the femoral head) in 1988 when the Exeter Universal stems were introduced. Further theoretical analysis59 suggested that the biomechanical basis for metal-backing was unsound and it also became apparent that the metal back was responsible for increased particulate debris formation and loosening, so that the metal back was abandoned in 1990. Others later reported similar experiences60,61.