CORROSION OF CEMENTED TITANIUM FEMORAL STEMS

Abstract

12 patients requiring revision of a cemented Furlong total hip replacement had advanced corrosion of their titanium femoral stems. Thigh pain unlike that of loosening was a characteristic feature of presentation an average 38 months after implantation (range 20–58 months). Radiographs demonstrated fusiform periosteal thickening of the middle and distal thirds of the femur around the prosthetic stem with variable amounts of osteolysis around the tip. None of the femoral stems showed evidence of loosening and in 9 cases revision was solely for recurrent atypical pain.

The titanium stems were retrieved at an average 80 months (range 60–113). All were well-fixed but showed signs of advanced corrosion distally with blackened stems, loss of surface metal and thick white deposits. Two stems were examined with scanning electron microscopy and energy dispersive X-ray analysis. Micromotion abrasions were identified proximally with loss of all alloy constituents. Distally, there was selective loss of titanium in a pattern suggestive of crevice corrosion. This may be accelerated by a galvanic effect if a cobalt chromium head is mixed with a titanium stem.

After revision to an all stainless steel femoral stem and head, early follow-up demonstrates resolution of both symptoms and radiological abnormalities at an average 13 months (range 3–33) from revision.

Conclusion: Once stem debonding has set up crevice conditions around a femoralimplant, the cement layer prevents repassivation (oxidation) of the metal surface upon which titanium depends for its stability. We therefore caution against the use of a titanium alloy stem with cementation, the conclusion of at least one other similar series. We also believe that the combination of cobalt chromium and titanium alloys is unsafe as, contrary to some of the published work on the subject, depassivated titanium is prone to galvanic attack in this situation.