Optimal orientation of implanted components in total hip arthroplasty with polyethylene on metal articulation

Background In many studies related to the total hip arthroplasty, it has been found that incorrect alignment of the total hip component is one of the major factors influencing mechanical failures. Although various recommendations for cup orientation have been presented, there were few studies that seek to determine a proper orientation of the implants based on the human motion data. The objective of this study is to determine an optimum orientation of the hip implant considering various daily activities. Methods Firstly, the cup orientations free of impingement were calculated for a given set of implant geometric parameters and the required range of motion for daily activities measured in 10 subjects. Next, the optimum values for the cup orientation and stem anteversion avoiding impingement and minimizing cup wear were determined for the proposed motion criteria. Findings Different cup orientation was obtained as optimum for each combination of the neck angles (40° and 50°) and oscillation angles (120° and 135°). The corresponding optimum stem anteversion was also different when different neck angle was used. Interpretation As the margin for the impingement-free orientation of the cup was small, the optimum cup orientation and stem anteversion should be adopted specific for each combination of the neck angle and oscillation angle.