The thrust plate prosthesis (TPP) is a hip prosthesis with metaphyseal fixation to the femur. Because the bone quality is reduced in patients with rheumatoid arthritis, this kind of fixation may have a higher failure rate than conventional stemmed endoprostheses in these patients. The aim of this investigation was to analyze the long-term results obtained with the TPP in patients with rheumatoid arthritis.
The survival of 51 implants in 46 patients with rheumatoid arthritis was analyzed. Clinical (Harris hip score) and radiological examinations were carried out on 47 of the 51 TPPs, with a post implantation follow-up period of at least 10 years. The Kaplan-Meier method was used to estimate the survival rates of the TPPs, with surgical revision due to the femoral implant as the endpoint of the investigation.
The Harris hip score increased from 42.4 ± 6.5 points preoperatively to 86.6 ± 10.1 points at follow-up. The failure rate was 23% (6 aseptic and 5 septic loosening). The total rate of revision amounted to 36.2% (17/47 TPPs): six aseptic loosening of TPPs, five septic loosening of TPPs, four aseptic loosening of the acetabular component, one removal of the fishplate of a TPP, and one femoral fracture. Additionally one TPP showed radiolucent lines indicating prosthetic loosening. Revision surgeries to stemmed endoprostheses of the hip were without severe problems in any patients.
The failure rate of the TPP was distinctly higher than that for conventional stemmed endoprostheses regarding aseptic and septic revisions. In cases with loosening of the TPP the preservation of the diaphyseal bone of the femur is poor and the TPP mostly needs a revision to a cemented stem. Thus, the estimated advantage of the TPP versus cementless stemmed prostheses for patients with rheumatoid arthritis is not evident. In conclusion, there is no evidence form this study to support the use of the TPP in this group of patients.