Friction of ceramic and metal hip hemi-endoprostheses against cadaveric acetabula

Introduction

Studies of hip arthroplasty have dealt mainly with total endoprosthesis, while tribology measurement values of hemi-endoprosthetic implants are rare. The small amount of experimental tribological data concerning materials of hemi-endoprosthetic implants in the form of pendulum trials, animal experiments, in vivo measurements on human hip joints and pin on disc studies report friction coefficients between 0.014 and 0.57; the friction coefficients measured in fresh human cadaver hip joints were determined between 0.001 and 0.08.

Materials and methods

The HEPFlEx-hip simulator was constructed to test the friction coefficients of unipolar femur head hemi-endoprostheses made of metal or ceramic against fresh cadaveric acetabula. Its plane of movement is uniaxial with a flexion-extension movement of +30/−18°. The force is produced pneumatically dynamic with amounts of 2.5 kN. Newborn calf serum serves as a lubricant. We mounted 20 fresh porcine acetabula and 10 fresh human cadaver acetabula in the HEPFlEx-hip simulator and compared the two unipolar femur head hemi-endoprostheses (metal vs. ceramic).

Results

The mean friction coefficients against porcine acetabula were µ=0.017–0.082 for ceramic and µ=0.020–0.101 for metal; against human cadaver acetabula µ=0.017–0.083 for ceramic and µ=0.019–0.118 for metal. The frictional coefficient deltas (metal-ceramic) values of all measurements were Δµ=0.004 for porcine acetabula and Δµ=0.001 for cadaver acetabula. Box-plots graphics document significantly lower frictional coefficients of the ceramics.

Conclusions

The lower frictional coefficients of ceramic compared to metal against fresh cadaveric acetabula may have a clinical impact on the process of the protrusion of the corresponding femoral head through the acetabulum.