RESEARCH ON A NEW TYPE OF SANDWICH CUP FOR TOTAL HIP REPLACEMENT

Abstract

INTRODUCTION At present, abrassion of the polyethylene material seems to be the most important factor participating in endoprosthesis loosening. Created is so called polyethylene granulum having a toxic effect and which is a major cause of osteolysis, gradual bone degeneration and subsequent prosthetic loosening. For this reason, the ceramic, A120 3, was .introduced to the design of the total hip replacement. As the best solution the application of the ceramics is to both parts of the prosthesis, i.e. to the head and the cup. The advantages of the fractional couple of ceramic-ceramic, concomitantly with the damping effect of the plastics, are combined in a new cup type, the so-named sandwich cup, presently now being developed in the Czech Republic. RESULTS The new sandwich cup is designed as a polyethylene cup with a ceramic Iining. The development of a new type of cup covered both the theoretical and experimental research. The contact pressure and contact surface were calculated by means of finite element methods (FEM) and compared with the value of contact pressure and surface of the polyethylene cup. The experimental research incorporated the measurement of the frictional resistance, fatigue and impact tests. Research on the influence of different lubricants was also carried out. The frictional resistance in the hip joint total prosthesis was measured by means of a testing device which was developed at the Czech Technical University. CONCLUSION The possibility of using the diameter differences of ceramic cup -ceramic heads ranging from 0.022 mm to 0.137 mm (instead of the value 0.01 mm reported in literature) showed to be effective on the basis of measurement of the frictional resistance. The new type of sandwich cup was developed, and, with very good results used at the Orthopaedic Clinic of Charles University in Prague. REFERENCES Ravaglioli A., Krajewski A., Biomechanics, Chapman & Hall, London 1992