Abstract
Introduction
Long-term success of the cementless acetabular component has been depends on amount of bone ingrowth around porous coated surface of the implant, which is mainly depends on primary stability, i.e. amount of micromotion at the implant-bone interface. The accurate positioning of the uncemented acetabular component and amount of interference fit (press-fit) at the rim of the acetabulum are necessary to reduce the implant-bone micromotion and that can be enhancing the bone ingrowth around the uncemented acetabular component. However, the effect of implant orientations and amount of press-fit on implant-bone micromotion around uncemented acetabular component has been relatively under investigated. The aim of the study is to identify the effect of acetabular component orientation on implant-bone relative micromotion around cementless metallic acetabular component.
Materials and Method
Three-dimensional finite element (FE) model of the intact and implanted pelvises were developed using CT-scan data [1]. Five implanted pelvises model, having fixed antiversion angle (25°) and different acetabular inclination angle (30°, 35°, 40°, 45° and 50°), were generated in order to understand the effect of implant orientation on implant-bone micromotion around uncemented metallic acetabular component. The CoCrMo alloy was chosen for the implant material, having 54 mm outer diameter and 48 mm bearing diameter [1]. Heterogeneous cancellous bone material properties were assigned using CT-scan data and power law relationship [1], whereas, the cortical bone was assumed homogeneous and isotropic [1]. In the implanted pelvises models, 1 mm diametric press-fit was simulated between the rim of the implant and surrounding bone. Six nodded surface-to-surface contact elements with coefficient of friction of 0.5 were assigned at the remaining portion of the implant–bone interface [1]. Twenty-one muscle forces and hip-joint forces corresponds to peak hip-joint force of a normal walking cycle (13%) were used for the applied loading condition. Fixed constrained was prescribed at the sacroiliac joint and pubis-symphysis [1]. A submodelling technique was implemented, in order to get more accurate result around implant-bone interface [1].
Results and Discussions
The peak implant-bone sliding interfacial micromotion was observed around 75 microns around superior and supero-posterior regions of the acetabulum, whereas, micromotion was below 50 microns around other regions (area). As compared to other regions, less implant-bone micromotions were observed at the central region of the acetabulum and anterior part of the acetabulum, where micromotions were varied in the range between 5 microns to 30 microns. Although, the generated peak implant-bone sliding micromotion around the uncemented acetabulum was not vary notably due to change in inclination angle of the acetabular component, changes in patterns of implant-bone micromotions were observed and as shown [Fig.1]. Results of the present study indicated that the positioning of the uncemented acetabular component have influence on patterns of implant-bone micromotion and that might have influence on bone ingrowth and long-term success of uncemented acetabular component.
