Unlike Acetabular Anteversion, Femoral Anteversion Is Not Associated with the Hip Coronal Morphotype: An Anatomic Basis for a New Hip Morphotype Classification at Total Hip Arthroplasty.

BACKGROUND Most femoral stem designs used in total hip arthroplasty (THA) take into account the proximal femoral morphotype in terms of lateralization and neck-shaft angle (NSA) but not version. The objective of this study was to analyze the acetabular anteversion and femoral anteversion (FA) values in a large cohort according to the 3-dimensional (3D) morphotype of the proximal femur. Our hypothesis was that FA is an anatomic parameter independent of the coronal morphotype (varus, neutral, valgus). METHODS A retrospective study based on prospectively collected data included all patients who underwent, from January 2009 to December 2021, a THA planned on the basis of a low-dose computed tomographic (CT) scan 3D. The anatomic acetabular anteversion was calculated in the anterior pelvic plane. The 3D volume models were used to measure the NSA and the FA. We used a multivariable linear regression model to assess the relationship between the NSA and the other hip parameters. RESULTS The study included 849 consecutive patients (430 women and 419 men), with a mean age of 62 ± 15 years and a mean body mass index of 26.8 ± 5.7 kg/m2. The etiology was primary osteoarthritis in 616 patients, osteonecrosis in 141 patients, and dysplasia in 92 patients. The mean NSA was 129° ± 7°. The femoral morphotype was vara in 112 cases and valga in 105 cases. Acetabular anteversion was significantly lower in the vara group (mean, 21° ± 9°) and higher in the valga group (mean, 26° ± 9°) compared with the neutral group (mean, 24° ± 8°) (p < 0.001). The FA did not vary significantly according to the femoral morphotype (mean, 20° ± 12°; p = 0.3), with no significant association found between the NSA and FA (β = -0.004 [95% confidence interval, -0.5 to 0.05]; p = 0.8). CONCLUSIONS The FA was not associated with the NSA. A hip morphotype classification combining the NSA and FA is presented for use in guiding preoperative planning in THA. Customized patient-specific stems may be of interest in some morphotypes to accurately restore the hip anatomy. LEVEL OF EVIDENCE Prognostic Level IV. See Instructions for Authors for a complete description of levels of evidence.