Effects of early and late stage cement intrusion into cancellous bone.

Minimizing aseptic loosening of cemented femoral stems in total hip arthroplasty remains a goal. Recent investigation suggests that improved cement intrusion may result from elevated pressures shown to occur during stem placement into higher viscosity late stage polymethylmethacrylate cement when compared with low viscosity early stage cement. The hypothesis tested is that placement of a femoral stem in late stage cement can increase cement-bone contact as compared with placement in early stage cement. The variable tested in this experiment was cement viscosity. Radiographic analysis was done on nine paired femurs from cadavers that had placement of a cemented femoral stem with either early or late stage polymethylmethacrylate. Radiographs were assessed quantitatively by measuring the extent of radiolucency observed at the cement-bone interface. Specimens that had late stage cement had significantly less radiolucency in the middle zone region, corresponding to combined Gruen Zones 2 and 6. Similar trends were observed in the proximal and distal zone regions of the stem. Elevated stem insertion pressure associated with late stage cement can minimize void space between the cement and trabecular bone. These findings suggest that the surgeon should consider femoral stem placement later in the cement cure cycle, generating higher intramedullary pressure, and leading to improved cement intrusion into the surrounding bone.