[Results after replacement of femoral neck prostheses - thrust plate prosthesis (TPP) versus ESKA cut prosthesis]

The aim of this study was to analyse and evaluate comparatively loosening mechanisms, failure frequency, surgical changing strategies and results after replacement of thrust plate prostheses (TPP) and ESKA Cut prostheses.

Between 1993 und 2007, 465 TPP and in the years 2000 and 2001 82 ESKA Cut prostheses were performed and evaluated prospectively. Until 2007 46 change interventions of the TPP and 35 of the CUT prosthesis became necessary. All patients who received a stem revision procedure in our hospital were included within this study. Besides the evaluation of clinical results according to the criteria of the Harris Hip Score on the average at 15.6 months (+/- 14.4) postoperatively, radiological loosening processes and surgical difficulties were registered. Furthermore, an analysis of perioperative data was performed according to some criteria of the German Federal Office of Quality Assurance (BQS), such as duration of the surgery, intraoperative blood loss and complications. Statistical investigations for comparative analysis as well as survival analysis of both groups were calculated using SPSS for Windows 13.0.

The mean age of the 46 patients who had to undergo revision surgery after TPP was 60.1 years, that of 35 patients in whom revision surgery was necessary after receiving an ESKA Cut femoral neck stem was 56.6 years. The survival rate analysis according to Kaplan-Meier at 13 years was 89.4 % (TPP) and 53.6 % at 66 months (ESKA Cut). In all cases the partial osteointegration of the tripod surface of the loosened Cut prosthesis complicated the explantation. It led on the one hand to a significant difference of the surgery duration and on the other hand to an increased frequency of fractures of the trochanteric region. The conversion of the TPP on standard type stems was usually free of problems. The HHS increased significantly to the averages of 86.6 (TPP) or, respectively, 91.69 (ESKA Cut) after revision.

In comparison with the usually problem-free changing procedure of the TPP to a standard type stem, the revision surgery of the Cut prosthesis becomes substantially more complex and leads frequently to complications. In view of unacceptable survival rates, the Cut prosthesis does not represent an alternative implant in young patients. Except for the implantation technique, which does not allow a less invasive surgical procedure, the TPP fulfils the requirements of femoral neck prosthesis due to acceptable survival rates and good convertibility.