The Effect of Overall Limb Torsion on Functional Femoral Version and Its Functional and Biomechanical Implications on Lower Limb Axial Anatomy: A Study on CT and EOS Imaging.

Background: Variations in femoral version are increasingly recognized as contributing factors to the development of symptomatic femoroacetabular impingement (FAI) and ischiofemoral impingement (IFI). Despite having implications for both hip arthroplasty and hip preservation surgery, functional femoral version (FFV) and overall limb torsion (OLT) are understudied. This study was conducted with the primary aim of defining and measuring FFV as a function of OLT. Methods: A cohort of 106 patients scheduled for primary hip arthroplasty underwent detailed retrospective assessment through CT and EOS imaging. Femoral torsion, transmalleolar axis, tibial torsion, trochanteric station and limb torsion were measured. The trochanteric station distance was also defined on both CT as well as on the lateral standing EOS. Statistical analyses examined the relationships between FFV, OLT, and other measurements. Results: Findings indicate a strong correlation between OLT and FFV. Agreement between CT and EOS imaging for trochanteric station was 0.88. Conclusions: The study reveals that OLT offers a more comprehensive assessment of impingement risk than anatomical femoral version alone. As OLT correlates with FFV, it highlights the role of axial limb alignment in hip joint biomechanics. Understanding the interplay between FFV and OLT can guide more individualized surgical techniques, potentially improving patient outcomes.