The effect of centrifugation on the fatigue life of bone cement in the presence of surface irregularities.

Reduction of the porosity of bone cement by centrifugation significantly improves the fatigue life of the cement when smooth, waisted specimens are tested. However, bone cement in vivo has surface irregularities at the interdigitation of the cement with the trabecular bone. The effect of centrifugation on the fatigue life of Simplex P in specimens containing surface irregularities was investigated by examining both composite specimens of trabecular bone and bone cement and specimens containing a sharp, circumferential notch. For the specimens with the sharp notch, the bone cement that had been centrifuged lasted significantly longer in fatigue (47,039 +/- 40,277 cycles) than the uncentrifuged specimens (3103 +/- 1950 cycles). Eleven of 15 uncentrifuged specimens broke at the location of a void, rather than the notch. In contrast, when the porosity was reduced by centrifugation, 13 of the 15 specimens broke at the notch. For the specimens that were a composite of bone cement and trabecular bone, the centrifuged specimens had a significant increase in fatigue life compared to the uncentrifuged specimens when tested at both 7 MPA (641,056 +/- 444,131 cycles vs. 237,969 +/- 124,153 cycles) and 15 MPA (8800 +/- 4673 cycles vs. 1534 +/- 719 cycles). Reduction of porosity in bone cement by centrifugation significantly extends its fatigue life even in the presence of trabecular bone or sharp surface notches as used in total joint replacements. These data support the concept that reduction of porosity of bone cement by centrifugation may extend the duration of fixation of the components in cemented total joint arthroplasties.