An Experimental Study of the Effect of Vacuum Mixing on Fatigue Characteristics of Acrylic Bone Cement

Shon, Won Yong; Lee, Seok Hyun; Park, Sang Won; Suh, Jeong Dae

Abstract

Contemporary cementing techniques improved the longevity of the cemented total hip replacement. The mechanical strength of acrylic bone cement can be changed by different handling techniques with reduction of the porosity of acrylic bone cement. The greatest improvement of the mechanical properties with reducing the porosity is that of the fatigue strength. We investigated the mechanical properties of the specimens of high viscosity, Palacos R(Merk, Darmstadt, FRG) bone cement with two mixing methods, hand and vacuum mixing. Vacuum mixing improved the ultimate tensile strength by 22.4% compared to hand mixing in previous study. For the uniaxial tension fatigue test, the specimens were cyclically loaded at a maximum stress of 25 MPa at a frequency of 2.5 Hz and to investigate the porosity, scanning electromicroscopic examination was taken in each hand mixed and vacuum mixed specimens. Scanning electromicrogram showed the vacuum mixed specimens to be the more uniform and free of small voids compared with the hand mixed specimens. The results of the fatigue test were analized using Weibull distribution of survival probability, the average number of cycles to failure was 1459±924 cycles in hand mixed specimens, in vacuum mixed specimens, 21491±14956 cycles. The average fatigue life of the vacuum mixed specimens was 15 times loanger than that of the hand mixed specimens by Weibull mean, this differene exists stastically within 95% confidence interval. We could suggest vacuum mixing technique as a method eliminating porosity in a chilled acrylic bone cement and thereby markedly improving the mechanical properties. In cemented joint replacement surgery, a vacuum mixing technique are recommended as a method of preparation of acrylic bone cement