Proximal cementation of a collarless polished tapered hip stem: biomechanical analysis using a validated finite element model

Total hip replacement (THR) with cemented stem is a common procedure for patients with hip osteoarthritis. When primary THR fails, removal of the cement is problematic and poses challenges during revision surgeries. The possibility of proximal partial cementing of the hip stem was explored to mitigate the problem. 3D finite element analysis was performed to investigate the feasibility of reduced cement length for effective implant fixation and load transmission. Three levels of cement reduction (40 mm, 80 mm, and 100 mm) in the femoral stem were evaluated. All models were assigned loadings of peak forces acting on the femur during walking and stair climbing. The experimental and predicted max/min principal bone strains were fitted into regression models and showed good correlations. FE results indicated stress increment in the femoral bone, stem, and cement due to cement reduction. A notable increase of bone stress was observed with large cement reduction of 80-100 mm, particularly in Gruen zones 3 and 5 during walking and Gruen zones 3 and 6 during stair climbing. The increase of cement stresses could be limited to 11% with a cement reduction of 40 mm. The findings suggested that a 40-mm cement reduction in hip stem fixation was desirable to avoid unwanted complications after cemented THR.