Klinische und Radiologische Ergebnisse nach Implantation der Druckscheibenendoprothese (DSP) bei Patienten mit Femurkopfnekrose

AIM: In this study, we investigated the results after implantation of the thrust plate prosthesis (TPP) in patients with femoral head necrosis. We intended to answer the question if the femoral neck prosthesis, inaugurated by Huggler and Jacob in Switzerland, which needs a good bone stock for a successful implantation, is a recommendable alternative to other cementless intramedullary fixed prostheses. METHOD: In a prospective study, 62 patients who had received 70 TPP because of femoral head necrosis as a result of various aetiologies between 1993 and 2004 were examined clinically and radiologically. The follow-up examinations were carried out 3 and 6 months postoperatively and subsequently once a year. The mean follow-up interval was 6.0 +/- 1.9 years (1.0-10.2 years). Clinical examination was carried out using the Harris hip score; the radiological examination was performed according to predefined criteria in an exact a.-p.-view. Four sectors can be distinguished: A corresponds to the femoral neck stump, B to the bony stock cranial (= 1) and caudal (= 2) to the mandrel of the prosthesis, C is the region above and under the bolt and D is the cortical area around the lateral plate. Furthermore, we performed a Kaplan-Meier survival rate analysis. RESULTS: We found excellent clinical results. The preoperative Harris score increased from 48.3 to 91.6 +/- 6.6 at 24 months after the operation. Radiolucencies of various relevancies were detected depending on the localisation. We often saw bony atrophy under the thrust plate (sector A: A 1 21.4%, A 2 9.9%) and small radiolucencies along the bolt (sector C 30 % in general). As a pathological finding we interpreted progressive radiolucencies of sector B, which was considered to be a sign of loosening, when they showed a thickness of > or = 2 mm. Therefore, we had to change one TPP. In two additional cases we saw an extended atrophy under the lateral plate, which was also interpreted to be a sign of loosening. The Kaplan-Meier survivorship analysis for 5 and 10 years was 95.1% (95% - 0.95 +/- 0.05). Our study suggests that, in spite of a slightly higher aseptic loosening rate in comparison with cementless stem prosthesis, the thrust plate prosthesis proved worthwhile. On account of our previous experience we consider the TPP to be a good alternative implant, especially for young patients. CONCLUSION: Due to excellent clinical results and nearly identical findings in the survivorship analysis in comparison to cementless stem prostheses, the TPP is also a good alternative implant for total hip arthroplasty in patients with femoral head necrosis. For a successful implantation of the TPP a good bone quality of the proximal femur is necessary. Therefore we cannot recommend the use of a thrust plate prosthesis in patients with femoral head necrosis and simultaneous osteopeny.