In vivo behavior of acrylic bone cement in total hip arthroplasty.

Polymethylmethacrylate (PMMA) bone cement serves as the primary fixation material between bone and the prosthetic component in cemented total hip arthroplasty. In vivo degradation of bone cement may lead to a decrease in mechanical properties of PMMA and result in aseptic loosening. However, other factors such as porosity and location of the cement relative to the bone implant interface may also contribute to mechanical behavior in vivo. This study investigated the mechanical properties of Simplex cement retrieved from 43 patients undergoing revision total hip arthroplasty. The time in vivo was between 1 month and 27 years. The variables studied included fracture toughness (KIC), porosity, molecular weight, time in vivo of the cement, and relative in vivo location of the cement with respect to the implant and bone. KIC did not correlate with time in vivo of the samples or with molecular weight. This suggests that time in vivo may not be the limiting factor in the mechanical integrity of the bone cement, A significant and inverse relationship was found between porosity and KIC. This implies that porosity is the most important factor in the mechanical behavior of bone cement during in vivo use.