Coexistence of dissimilar metals after conversion of intertrochanteric osteotomy to total hip arthroplasty. 18 patients followed for 5-20 years after conversion.

Extraction of an internal fixation device during the conversion of a failed intertrochanteric osteotomy to a total hip arthroplasty (THR) may lead to excessive trauma of the femoral shaft. In an attempt to bypass this risk, we performed THR leaving the old osteosynthetic material (straight plates and screws) in 10 of 48 patients operated on during the last 20 years. In another 8 patients, most of the osteosynthetic material was removed, but screw fragments were left in the canal. Insertion of the cement and the stem was unexpectedly easy in all 18 cases. After a mean follow-up of 10 (5-20) years there were no clinical problems. Radiographically, there were no signs of loosening, with only an occasional slight osteoporosis of the greater trochanter. Although theoretically the coexistence of different metals in the shaft should be avoided, in practice it does not appear to create a problem for patients. This may be attributed to insulation of the dissimilar materials by the cement. In conclusion, in cases where removal of the osteosynthetic device is expected to lead to severe trauma of the femur, our findings indicate that it is no disadvantage to perform the THR leaving the internal fixation material in place.