Effects of pre-heating procedures on cement polymerization and thermal osteonecrosis in cemented hip replacements
We would like to thank Drs. Talbot and Shaw [1] for their interest in our paper [2] and for raising several important issues related to that work. We thank the authors for introducing us to the work of [3] and [4]. We are aware of the other work referenced in their letter.
We agree fully that most necrosis in cemented implant procedures is not due to thermal heating alone, and we never intended to state otherwise. Realizing this, our paper emphasized thermal necrosis as one of several possible mechanisms. Drs. Talbot and Shaw suggested that we concluded that preheating the prosthesis does not result in osteonecrosis at all, but we do not have such a conclusion in the paper, and we agree that there are multiple sources of osteonecrosis. We did conclude that pre-heating the implant does not result in significant thermal osteonecrosis, which we feel is a valid conclusion. In regard to other sources of necrosis, we claim no conclusions about the effects of pre-heating on them. It is, however, worthwhile to note that the residual monomer level may be decreased by the pre-heating procedure [5]. This may help to reduce chemical osteonecrosis as well, although more study is required to support this statement. We also conclude that pre-heating the prosthesis prior to the implantation may decrease the likelihood of cement-prosthesis loosening and increase the life of hip arthroplasty. This conclusion is based on the fact that the propensity for void formation is moved away from the cement-implant interface, not on the fact that thermal osteonecrosis is reduced.
We concur that we simplified the conditions in the finite element analyses. For example, the cancellous bone porous structure, the interfacial thermal resistance at the cement-bone interface, reaction incompletion and the presence of physiological blood flow are not taken into account in the model. We expressly stated this in the discussion section of our paper, so we are not sure why Drs. Talbot and Shaw suggested this as an oversight. However, we do not agree that irregularity of the surface of the cancellous bone at the bone-cement interface will increase the dispersion of