Crevice corrosion of cemented titanium alloy stems in total hip replacements

Twenty-eight cemented Müller 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 months on average after implantation. The character of pain was dull, permanent, and increased at rest. Some patients reported pain relief while walking. Revisions were performed on average 25.5 months after primary implantation. Data from medical records, radiographs, histology of tissues taken at revision surgery, intraoperative pH measurements, examination of retrieved stems and bone cement fragments were gathered. In the radiographs debonding was visible only in 3 cases; a spindle shaped thickening of the femora occurred 9 months on average after recurrence of pain. After a further 11 months (average), scalloping osteolyses 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 bone interface. The distal surfaces of the stems were corroded at a higher rate, whereas the proximal regions more often were subject to abrasion. Measurements of the pH of the corroded stems revealed values of high acidity. Recurrence of pain and subperiosteal apposition of bone are due to diffusion of acid; subsequent scalloping osteolyses develop due to particle induced foreign body granulomas. The mechanism of crevice corrosion of cemented titanium based alloys does not seem applicable to cobalt and iron based implant alloys. Titanium alloys can no longer be recommended for cementation, but are as safe as ever for anchorage without cement.