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Background: Femoral offset and anteversion have been reported to affect the incidence of dislocation following bipolar hemiarthroplasty, although the magnitudes of contributions of the femoral offset and stem anteversion on dislocation, both singly and in combination is not fully understood., Methods: Using the CT data of 61 patients (61 hips), including 30 male and 31 female who underwent bipolar hemiarthroplasty, three-dimensional dynamic motion analysis was performed using a modular implant that enabled adjustment of femoral offset and stem anteversion independently. The pattern of impingement and relationship between femoral offset/stem anteversion and range of motion were evaluated using the software., Findings: We found that a higher femoral offset and stem anteversion correlate with a greater range of motion of flexion and internal rotation. Furthermore, an increased femoral offset has a great effect on increasing range of motion of flexion than stem anteversion, and increased both femoral offset and stem anteversion have fewer effect on the flexion, whereas increasing stem anteversion has a great impact on internal rotation than offset, especially in the case with lower femoral anteversion. However, a higher stem anteversion decrease the range of motion of external rotation, whereas a higher femoral offset leads to an increased range of motion of external rotation., Interpretation: We demonstrated that both a higher femoral offset and stem anteversion substantially affected the range of motion in flexion, internal rotation and external rotation. However, these are not independent, but rather mutually confounding, the surgeons should consider retaining femoral/anterior offset in bipolar hemiarthroplasty., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022. Published by Elsevier Ltd.)

Background: We aimed to evaluate the associations between implant alignment/position and patient-reported outcomes following total hip arthroplasty using CT-based simulation software., Methods: We reviewed hips of 137 patients (27 males, 110 females, mean age: 67.3 years old) who underwent total hip arthroplasty. Radiographic evaluations were based on the software for evaluation of the parameters related to implant alignment/position and femoral/3-dimensional offset using post-operative CT data. Pre-operative and one-year post-operative patient-reported outcomes using Japanese Orthopaedic Association Hip Disease Evaluation Questionnaire scores were evaluated., Findings: The total and movement scores of normal combined anteversion and stem anteversion angle groups were significantly higher than those of lower and higher groups. The pain and movement scores of decreased femoral offset group were significantly lower than those of restored and increased femoral offset group. There were no significant differences in all scores in cup inclination and anteversion angle, stem coronal alignment, and 3-dimensional femoral offset among groups. Moreover, investigation of the associations between combined anteversion angle/stem anteversion/femoral offset and movement scores revealed that combined anteversion angle and stem anteversion were significantly associated with the movement that needs deep hip flexion and occasionally deep abduction, and high femoral offset was also associated with the movement that needs deep hip flexion., Interpretation: Surgeons should consider the stem anteversion, stem sagittal alignment, and combined anteversion, in addition to the femoral offset to achieve patient's post-operative satisfaction, although the surgeon may have a relatively larger choice for the implant positioning, especially on the cup side., (Copyright © 2022. Published by Elsevier Ltd.)