Intraoperative estimation of natural femoral anteversion from proximal femoral osseous orientation during total hip arthroplasty.

BACKGROUND: The purpose of this study was to elucidate the relationship between the orientation of the osseous structure of the proximal femur encountered during total hip arthroplasty (THA) and preoperative femoral anteversion (FA). METHODS: Three-dimensional models were constructed using full-length lower extremity computed tomography images from a total of 80 participants. Femoral neck cutting was performed at heights of 5, 10, and 15 mm relative to the lesser trochanter. Following neck cutting, the angles formed by the anterior outer cortex and posterior outer cortex with the posterior condylar line (PCL) were defined as the anterior cortical angle (ACA) and posterior cortical angle (PCA), respectively. Univariate linear regression analysis was conducted using the remaining measurements with FA as the dependent variable. RESULTS: The mean age of the participants was 60.98 ± 10.82 years (males, 60.50 ± 11.36 years; females, 61.45 ± 10.37 years) (p = 0.697). All cortical angles and FA were larger in women compared to those in men. When comparing measurements by age groups, no statistically significant differences were observed. Univariate linear regression analysis with FA as the dependent variable showed statistical significance for all cortical angles. The adjusted R2 values were 0.711 (ACA5), 0.677 (ACA10), 0.572 (ACA15), 0.493 (PCA5), 0.574 (PCA10), and 0.446 (PCA15). CONCLUSION: Natural FA can be inferred from the anterior cortical angle (ACA) from femoral neck cutting plane observed during the THA procedure without preoperative images. TRIAL REGISTRATION: Retrospectively registered.