A new approach to quantify trabecular resorption adjacent to cemented knee arthroplasty

A new micro-computed tomography (mu CT) image processing approach to estimate the loss of cement-bone interlock was developed using the concept that PMMA cement flows and cures around trabeculae during the total knee arthroplasty procedure. The initial mold shape of PMMA cement was used to estimate the amount of interdigitated bone at the time of implantation and following in vivo service using enbloc human postmortem retrievals. Laboratory prepared specimens, where there would be no biological bone resorption, were used as controls to validate the approach and estimate errors. The image processing technique consisted of identifying bone and cement from the mu CT scan set, dilation of the cement to identify the cement cavity space, and Boolean operations to identify the different components of the interdigitated cement-bone regions. For laboratory prepared specimens, there were small errors in the estimated resorbed bone volume fraction (reBVfr=0.11 +/- 0.09) and loss in contact area fraction (CAfr=0.06 +/- 0.15). These values would be zero if there were no error in the method. For the postmortem specimens, the resorbed volume fraction (reBVfr=0.85 +/- 0.16) was large, meaning that only 15% of the cement mold shape was still filled with bone. The loss of contact area fraction (CAfr=0.84 +/- 0.17) was similarly large. This new approach provides a convenient method to visualize and quantify trabecular bone loss from interdigitated regions from postmortem retrievals. The technique also illustrates for the first time that there are dramatic changes in how bone is fixed to cement following in vivo service. (C) 2011 Elsevier Ltd. All rights reserved.