An implant for an articulating two-component joint, said implant comprising a sac and a filler material located within the sac, said sac having an external surface which in use contacts bone or cartilage of the joint and which has a coefficient of friction such that it does not move relative to the bone or cartilage with which it is in contact during articulation and said filler has a coefficient of friction that allows opposite sides of the sac to move relative to one another when a force is applied.
