Effect of Implant Positioning in Cemented Hip Arthroplasty

The positioning of a cemented total hip arthroplasty (THA) is a crucial factor during the surgical implantation procedure. However, the impact of misalignment on stress distribution at the cement mantle and bone remains poorly understood, posing a potential risk for periprosthetic bone fracture. This study explores the effects of hip stem positioning in cemented THA by using finite element analysis (FEA). The aim is to investigate the impact of implant position on stress and deformation distributions at the contacting components, i.e. femoral bone, cement, and hip stem, under walking and stair-climbing activity’s forces. The rotating angles of -0.75°, -0.5°, -0.25°, 0.25°, 0.5°, and 0.75° are used at the varus plane with the distal end of the stem as the centre of rotation. The unrotated condition (at an angle of 0°) is simulated as the baseline condition of normal hip stem position. Results indicate that the baseline angle of 0° position does not necessarily represent the lowest stress and deformation in the femoral bone. Furthermore, misalignment angle variations at varus planes minimally affect total deformation but significantly impact stress distribution at the cement mantle. These findings underscore the importance of considering alignment angles beyond the baseline and their effects on stress and deformation in cemented THA.