Effects of small angular variations in implant positioning on stability of cemented Total Hip Arthroplasty

Total Hip Arthroplasty (THA) is a widely performed surgical procedure in which an artificial prosthesis replaces a diseased or fractured hip joint. An important factor in determining primary stability and long-term mechanical performance in cemented total hip arthroplasty is implant orientation. This study aims to predict the effects of implant positioning at varus and sagittal to implant stability in hip arthroplasty. Using finite element analysis (FEA), this study examined how sagittal and varus angular positioning affected the stress, strain, and deformation responses of a cemented THA. Computed tomography (CT) data was used to reconstruct a three-dimensional femur model, and Abaqus was used to model a cemented THA assembly that included an femur (σy= 115 MPa), cement mantle (σy= 29 MPa), and hip implant (σy= 205 MPa). The findings show that even little variations in implant placement have a significant impact on cement mantle stress and deformation. Maximum stress and deformation occurred at 0.3° (24.62 MPa and 10.29 µm, respectively) in sagittal positioning and -0.25° (20.19 MPa and 10.33 µm) in varus positioning during stair climbing. Implant stability is reflected in the mechanical reaction of the cement mantle, which mediates load transfer between the implant and bone. Although stresses remained below the PMMA yield strength, misalignment of implants may still increase fatigue-related risk, potentially compromising stability.