Abstract
Introduction
Hip resurfacing arthroplasty has gained popularity as an alternative for total hip arthroplasty. Usually, cemented fixation is used for the femoral component. However, each type of resurfacing design has its own recommended cementing technique.
In a recent investigation the effect of various cementing techniques on cement mantle properties was studied. This study showed distinct differences in cement mantle volume, filling index and morphology.
In this study, we investigated the effect of these cement mantle variations on the heat generation during polymerization, and its consequences in terms of thermal bone necrosis.
Materials and methods
Two FEA models of resurfacing reconstructions were created based on CT-data of in vitroimplantations (Fig 1). The two models had distinct differences with respect to the amount of cement that was used for fixation. The first model was based on an implantation with low-viscosity cement, with anchoring holes drilled in the bone, and suction applied to maximize cement penetration. The second model was based on an implantation with medium viscosity cement smeared onto the bone, with no holes and no suction, leading to a thin cement layer.
Thermal analyses were performed of the polymerization process, simulating three different types of bone cement: Simplex P (Stryker), CMW3 (DePuy J&J) and Osteobond (Zimmer), with distinct differences in polymerization characteristics. The polymerization kinematics were based on data reported previously.
During the polymerization simulations the cement and bone temperature were monitored. Based on the local temperature and time of exposure, the occurrence of thermal bone necrosis was predicted. The total volume of necrotic bone was calculated for each case.
Results and discussion
The simulations showed distinct differences between the temperature distributions in the various models. The highest temperature was found in the CMW3 model with a large cement volume (Fig. 2, Table 1), while the Osteobond model with a thin cement mantle produced the lowest temperature rise in the bone.
The necrotic bone volume was highest in the CMW3 model with a large cement mantle, while the lowest volume was found in the model with a thin cement layer (Table 1).
Assuming that the bone that is being penetrated by cement also is affected by thermal and toxic necrosis, more than 70% of the bone inside the resurfacing implant may become necrotic. In contrast, when using a less invasive cementing technique, thermal necrosis can be reduced to approximately 20% of the volume inside the resurfacing implant. A large zone of necrotic bone at the cement-bone interface may have serious implications for the strength and stability of resurfacing arthroplasty.
Conclusion
We conclude that the cementing technique and type of cement used for fixation of a resurfacing implant can dramatically affect the viability of the femoral bone, and therefore the survival of the reconstruction. Thermal necrosis may be reduced by minimizing cement penetration, although this may also have consequences for the mechanical stability.
