Abstract: BACKGROUND: Coronal prosthetic alignment of femoral stems significantly influences the prognosis of total hip arthroplasty. Currently, systematic analysis of the relationship between proximal femoral anatomical parameters and femoral stem prosthetic alignment remains insufficiently explored, and the quantitative impact of critical anatomical parameter thresholds on coronal varus implantation remains unelucidated.
OBJECTIVE: To explore the effects of proximal femoral morphology and angular parameters on coronal varus alignment of uncemented femoral stems in total hip arthroplasty, determine predictive thresholds for key parameters, and construct a risk assessment model to provide clinical decision-making support for preoperative planning and surgical strategies of total hip arthroplasty.
METHODS: Medical records of 276 cases undergoing primary total hip arthroplasty between January 2022 and December 2024 were retrospectively enrolled. Uncemented femoral stems were implanted via an anterolateral approach. Preoperative anatomical parameters of the affected proximal femur were measured: neck-shaft angle, femoral cortical index, canal flare index, and greater trochanter base to lateral cortical perpendicular intersection ratio. At 1 month postoperatively, cases were divided into a varus group (<−3°) and a non-varus group (≥−3°) based on the angle between the femoral stem axis and femoral medullary canal axis. Univariate analysis, receiver operating characteristic curve analysis, and multivariate logistic regression were employed to evaluate correlations between anatomical parameters and varus alignment.
RESULTS AND CONCLUSION: (1) A total of 139 patients were included (varus group: 32 cases; non-varus group: 107 cases). (2) Univariate analysis demonstrated that the varus group had a smaller neck-shaft angle (P < 0.001) and higher greater trochanter base to lateral cortical perpendicular intersection ratio (P < 0.001) than the non-varus group. (3) Receiver operating characteristic curve analysis identified thresholds for varus prediction: neck-shaft angle ≤ 127.6° (area under the curve = 0.713) and greater trochanter base to lateral cortical perpendicular intersection ratio > 0.52 (area under the curve = 0.724). The area under the curve of combined prediction for neck-shaft angle and greater trochanter base to lateral cortical perpendicular intersection ratio was 0.772, demonstrating higher predictive efficacy than individual parameters. (4) Multivariate logistic regression confirmed that neck-shaft angle ≤ 127.6°and greater trochanter base to lateral cortical perpendicular intersection ratio > 0.52 were independent risk factors. (5) In summary, neck-shaft angle and greater trochanter base to lateral cortical perpendicular intersection ratio are independent risk factors for coronal varus alignment of uncemented femoral stems in total hip arthroplasty. The combined predictive model outperformed single parameters. Preoperative precise measurement of neck-shaft angle and greater trochanter base to lateral cortical perpendicular intersection ratio can guide prosthesis selection, optimize femoral prosthesis alignment strategies during total hip arthroplasty, and decrease the risk of varus implantation.

Key words: ">total hip arthroplasty, femoral stem, coronal alignment, varus, neck-shaft angle, femoral cortical index, canal flare index