Abstract
Introduction
Uncemented porous coated acetabular components have gained more research emphasis in recent years compared to their cemented counterparts, largely owing to the natural biological fixation they offer. Nevertheless, sufficient peri-prosthetic bone ingrowth is essential for long-term fixation of such uncemented acetabular components. The phenomenon of bone ingrowth can be predicted based on mechanoregulatory principles of primary bone fracture healing. Literature review reveals that the surface texture of implant plays a major role in implant-bone fixation mechanism. A few insilico models based on 2-D microscale finite elements (FE) were reported in literatures to predict the influence of surface texture designs on peri-prosthetic bone ingrowth. However, most of these studies were based on FE models of dental implants. The primary objective of this study, therefore, is to mechanobiologically predict the influence of surface texture on bone- ingrowth in acetabular components considering a novel 3-D mesh-shaped surface texture on the implant.
Materials/Methods
The 3-D microscale model [Fig.1] of implant-bone interface was developed using CATIA® V5R20 software (DassaultSystèmes, France) and was modelled in ANSYS V15.0 FE software (Ansys Inc., PA, USA) using coupled linear elastic ten-noded tetrahedral finite elements. The model consists of cast-inbeaded mesh textured implant having finely meshed inter-bead spacing. Linear, elastic and isotropic material properties considering Young's modulus of 210 GPa and Poisson's ratio of 0.3 for stainless steel implant were employed in the model. Boundary of bone was assumed to be rich in Mesenchymal Stem Cells(MSC) with periodic boundary conditions at contralateral surfaces. The linear elastic material properties in the model were updated iteratively through a tissue differentiation algorithm that works on the principle of mechanotransduction driven by local mechanical stimuli, e.g. hydrostatic pressure and equivalent deviatoric strain.
Results
Results indicate that bone ingrowth is inhibited upon increasing the inter-bead spacing and upon decreasing the bead aspect ratio. It has been observed that there is a predominant influence of bead spacing diameter on the peri-acetabular bone ingrowth. The increase in bead spacing diameter has led to increased bead height that is found to promote higher bone ingrowth with an increase in average Young's modulus of neo-tissue layer.
Conclusions
The present study focussed on the development of a new texture on the implant surface and to study the influence of surface texture on bone-ingrowth in acetabular components. Since there is a promising increase in average Young's modulus of the newly formed tissue layer, it predicts the increase in stiffness of the newly formed tissue. The increase in tissue stiffness reveals that, there is not much inhibition in bone ingrowth after the employment of the acetabular implant. The numerical study based on mechanoregulatory algorithm considering the appropriate mechanical stimuli responsible for bone ingrowth, reveals that, compared to hemispherical beaded surface texture, mesh shaped surface texture provides an improved fixation of the acetabular component.
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