CREVICE CORROSION OF CEMENTED TITANIUM-ALLOY STEMS IN TOTAL HIP REPLACEMENTS

Twenty-eight cemented Muller straight femoral stems of titanium forged alloys were mainly revised for causing pain in the patient, The pain pattern differed from aseptic loosening and pain recurred only 14.5 mo nths on average after implantation. The character of pain was dull, pe rmanent, and increased at rest, Some patients reported pain relief whi le walking, Revisions were performed on average 25.5 months after prim ary implantation, Data from medical records, radiographs, histology of tissues taken at revision surgery, intraoperative pH measurements, ex amination of retrieved stems and bone cement fragments were gathered. In the radiographs debonding was visible only in 3 cases; a spindle sh aped thickening of the femora occurred 9 months on average after recur rence of pain, After a further 11 months (average), scalloping osteoly ses appeared, Abraded particles like metallic titanium alloy, titanium corrosion products, polymethylmethacrylate, xray contrast medium, and polyethylene were detected, Metallic particles dominated in the joint capsule whereas more corrosion products impregnated the cement to bon e interface, The distal surfaces of the stems were corroded at a highe r rate, whereas the proximal regions more often were subject to abrasi on, Measurements of the pH of the corroded stems revealed values of hi gh acidity, Recurrence of pain and subperiosteal apposition of bone ar e due to diffusion of acid; subsequent scalloping osteolyses develop d ue to particle induced foreign body granulomas. The mechanism of crevi ce corrosion of cemented titanium based alloys does not seem applicabl e to cobalt and iron based implant alloys. Titanium alloys can no long er be recommended for cementation, but are as safe as ever for anchora ge without cement.