Can version of the proximal femur be used for CT planning uncemented femoral stems?

Three-Dimensional Computed Tomography (3D-CT) planning can predict the prosthetic femoral size in uncemented primary Total Hip Arthroplasty (THA). Correct sizing usually results in optimal varus/valgus femoral alignment; however, its effect on the Prosthetic Femoral Version (PFV) is poorly understood. Most 3D-CT planning systems use Native Femoral Version (NFV) to plan PFV. We aimed to assess the relationship between PFV and NFV in primary uncemented THA using 3D-CT analysis. Pre- and post-operative CT data was retrospectively collected from 73 patients (81 hips) undergoing primary uncemented THA with a straight-tapered stem. 3D-CT models were used to measure PFV and NFV. The clinical outcomes were evaluated. The discrepancy between PFV and NFV was low (<5°) in 43%, moderate (5-10°) in 40%, high (10-15°) in 11% and very high (>15°) in 6% of the cases. We found that NFV is not a useable guide for planning PFV. The 95% limits of agreement were both high at 17° and 15°, respectively. Satisfactory clinical outcomes were recorded. The discrepancy was large enough to recommend against the use of NFV for planning PFV when using straight-tapered uncemented stems. Further work should focus on the internal bony anatomy and the influence of stem design when planning uncemented femoral stems.