Assessing Anatomical Variability of the Proximal Femur in THA

Overview

This study developed a sex-specific statistical shape model (SSM) to quantify 3D morphological variability of the proximal femur before and after total hip arthroplasty (THA). It highlights the wide anatomical diversity influencing prosthetic femoral version (PFV) and the challenges in predicting PFV based on native femoral anatomy.

Background

In cementless THA, it is often assumed that native femoral version (NFV) correlates with prosthetic femoral version (PFV), but this is inaccurate due to variability in femoral canal anatomy. The PFV achieved can range widely, affecting implant fixation and biomechanics. Various femoral stem designs have been developed to address this variability, yet predicting PFV remains uncertain. Accurate preoperative prediction of PFV could guide fixation method choice and improve surgical outcomes.

Data Highlights

The study analyzed 62 pre- and post-operative CT scans (31 male, 31 female) of patients undergoing THA with a single femoral stem design (Quadra®–H). The mean age was 66 ± 11 years for females and 60 ± 13 years for males. A patient-specific femoral neck osteotomy guide was used to standardize the neck cut. The statistical shape model incorporated four regions of interest: native proximal femur, femur after neck osteotomy, internal femoral canal, and reconstructed femur with stem.

Key Findings

• There is significant 3D morphological variability in the proximal femur anatomy across patients, influencing PFV outcomes.
• The native femoral version does not reliably predict the prosthetic femoral version achieved postoperatively.
• The internal femoral canal shape is highly variable and dictates the achievable stem orientation and fixation.
• Use of a patient-specific femoral neck osteotomy guide ensures reproducible neck cuts, aiding in accurate modeling.
• The developed sex-specific SSM allows quantification of anatomical features and principal components relevant to femoral morphology.
• Current stem designs and intraoperative adjustments have limited ability to control PFV due to anatomical constraints.

Clinical Implications

Understanding the anatomical diversity of the proximal femur is critical for preoperative planning in cementless THA. The use of statistical shape models may improve prediction of prosthetic femoral version, guiding implant selection and fixation strategy. Surgeons should be aware of the limitations in adjusting stem rotation intraoperatively and consider patient-specific anatomy when planning surgery.

Conclusion

This study provides a detailed quantification of proximal femoral anatomical variability and underscores the challenges in predicting prosthetic femoral version. The sex-specific statistical shape model developed offers a foundation for improving preoperative planning and personalized implant selection in total hip arthroplasty.

References

1. Medacta International -- Quadra®–H femoral stem
2. Previous 3D-CT study validating osteotomy guide accuracy