Can any metal ball head be used for the metal-metal counterface pairing?
Absolutely not. Only SM® 21 ball heads are manufactured from a suitable cobalt-chromium alloy and have the necessary surface quality and close dimensional tolerances. Unlike hard-soft pairings, in which the soft partner can adapt to the hard material, with hard-hard counterface pairings the manufacturing tolerances are much closer and the degree of precision correspondingly higher. For this reason a metal cup insert must only be paired with the SM® 21 ball head; otherwise metallosis and subsequent necrosis of the surrounding tissue would occur. If, following surgery, it is found that an incorrect metal pairing has been used then prompt revision is required to change the ball head and cup insert. No compromises are permitted in such cases.
