Fracture characteristics of acrylic bone cement-bone composites.

In this study, the fracture properties of Perspex, acrylic bone cement prepared using a commercially available reduced pressure mixing system and a bone cement-bone composite were compared under different test conditions. The method used was the double-torsion (DT) test. The observations made from this investigation are as follows. The fracture toughness and critical crack length for Perspex significantly increased (ANOVA, p = 0.001) when tested in water compared to air. An increase in test temperature from 19 to 37 degrees C resulted in a decrease in the fracture properties in water, this reduction being also statistically significant (ANOVA, p = 0.02). The mean fracture toughness and standard deviation of CMW3 bone cement when mixed under reduced pressure was 2.19 +/- 0.11 MN m(-3/2) compared to 3.89 +/- 0.10 MN m(-3/2) for the cement-bone composite (ANOVA, p = 0.004). The crack length determined for CMW3 bone cement and the cement bone composite were 0.323 +/- 0.031 and 1.1434 +/- 0.61 mm respectively. The plateau loads of the composite material were higher than measured for the monolithic acrylic bone cement, 249.66 +/- 67.75 N compared with 140.83 +/- 6.82 N. The high level of variation recorded for the plateau loads of the bone cement bone composite is due to the orientation and volume fraction of the cancellous bone. It can be concluded from this investigation that acrylic bone cement interdigitation into the cancellous bone results in a superior material with respect to crack resistance in comparison with the bone cement as a lone entity. Therefore it is an advantage if there is sufficient cancellous bone stock available within the intermedullary canal to allow bone cement penetration to occur, for the transfer of loads during daily activity. Additionally, it is paramount that the clinician ensures that adequate pressure is applied and maintained for an appropriate time during cement injection and prosthesis insertion in order to ensure optimum cement penetration into the pore openings of the cancellous bone, thus improving the resistance of the cement mantle to fracture and ultimately improving the longevity of the joint replacement.

Cement penetration in the proximal femur does not depend on broach surface finish.

In a cadaver study, we prepared 29 paired human cadaver femora using 3 different broaches of identical geometry but different surface characteristics. In one group of 20 pairs, preparation with chipped-toothed broaches was compared to diamond-shaped broaches; in the other group of 9 pairs, polished tamps for compaction of cancellous bone were compared with chipped-tooth broaches. Cancellous bone was irrigated with 1 liter pulsed lavage. The specimens were embedded in specially-designed pots. Palacos R and Simplex bone cements were used. After vacuum mixing, the cement was applied in a retrograde manner and subjected to a standard pressure protocol with a constant force of 3,000 N. Radiographs were taken and horizontal sections were obtained at predefined levels using a diamond saw. Microradiographs were taken, digitized and analyzed to assess cement penetration into cancellous bone. In 6 of 9 femora prepared using smooth tamps, femoral fractures occurred despite careful preparation technique. The microradiographic evaluation showed no significant morphometric differences between diamond and chipped-tooth or between polished and chipped-tooth broaches with regard to cement penetration into cancellous bone. Therefore, in the presence of pulsed lavage, one finds no significant effect of broach surface characteristics on cement penetration into cancellous bone of the proximal end of the femur.