Quantifying the anatomical variability of the proximal femur

Achieving a prosthetic femoral version (PFV) within the target range of 10-20° is crucial for optimal biomechanics in total hip arthroplasty (THA). Predicting the PFV preoperatively is challenging due to the limited understanding of the relationship between native femoral version (NFV) and the morphology of the intramedullary canal. This study aims to quantify the 3D morphological variability and identify the most variable anatomical features of the proximal femur pre- and post-operatively.

Pre- and post-operative CT scans from 62 patients (31 males, 31 females) who underwent THA and received a single stem design (straight, triple-tapered) were analysed. Four femoral models were generated per patient: 1. Native proximal femur, 2. Native femur after neck osteotomy, 3. Internal femoral canal after neck osteotomy, and 4. Reconstructed femur. Statistical Shape Models (SSMs) were developed separately by sex, and principal component analysis (PCA) was used to identify dominant modes of anatomical variation.

The first three principal components (PCs) accounted for over 60% of shape variability across all models. PFV showed weak correlation with NFV as variability existed between the SSM of the internal femoral canal and SSM of the native proximal femur. Sex-specific differences in the measured NFV and PFV were found, with females exhibiting a greater range and a more anteverted femur/femoral stem. The female canal model showed intramedullary version variability; however, this variability was not present in the first three PCs in the corresponding male model.

This study demonstrates that PFV cannot be reliably predicted from NFV alone. These findings underscore the need for advanced, 3D preoperative planning tools to better predict stem version and accommodate patient-specific anatomy. Additionally, the increased variability observed in females may warrant sex-specific consideration in implant design choice and surgical technique.