Background and purpose: Conversion total hip replacement (THR) is a common procedure after failed hemiarthroplasty, but there have been few reports describing the long-term outcome of this procedure.
Patients and methods: Between 1987 and 2004, 595 THRs were reported to the Norwegian Arthroplasty Register as conversion THR for failed hemiarthroplasty after a femoral neck fracture in patients aged 60 years and older. 122 operations left the femoral stem intact, whereas 473 were converted with exchange of the femoral stem.
Results: We found a lower risk of failure (revision surgery for any reason) for the conversion procedures with stem exchange (RR=0.4; 95% CI: 0.25-0.81) than for the conversion procedures that retained the femoral stem. For the 473 conversion arthroplasties with exchange of the stem, we found no difference in risk of failure compared to all revision stems in the register, either for the complete prosthesis (RR=0.8; CI: 0.50- 1.20) or for the stem (RR=0.9; CI: 0.53-1.59). However, for the 122 conversion procedures in which the femoral stem was retained, we found a significantly increased risk of failure for both the complete prosthesis (RR=4.6; CI: 2.8-7.6) and for the acetabular cup (RR=4.8; CI: 2.3-10) compared to primary hip arthroplasties.
Interpretation: Our findings indicate that the seemingly easy operation of implanting an acetabular cup to convert a hemiarthroplasty to a total hip arthroplasty is an uncertain procedure and that the threshold for replacing the stem should be low.