Total hip arthroplasty planning : Limits of x-ray and contribution of the CT-scan

Background: Traditional preoperative planning for total hip arthroplasty relies on two-dimensional radiography, which is prone to inaccuracies due to magnification errors, pelvic tilt, and patient positioning. These limitations often result in suboptimal restoration of limb length and femoral offset, potentially compromising functional outcomes and joint stability.

Objective: This article evaluates the clinical application and technical advantages of three-dimensional CT-based planning software compared to conventional radiographic templating in primary and revision hip arthroplasty.

Key Points: Analysis of 472 arthroplasties performed between 2008 and 2014 demonstrated that CT-based planning provides sub-millimetric precision across six standardized steps, including limb length measurement, Hounsfield bone density evaluation, and Lewinnek plane orientation. While radiographic templating shows less than 50% concordance with implanted component sizes due to variable magnification (110%–120%), CT-based planning achieved 94% to 100% accuracy for acetabular and femoral sizing. Specifically, CT allows for precise quantification of femoral torsion and offset, the latter of which is frequently underestimated by up to 10 mm on standard radiographs. In 3.4% of cases involving complex femoral morphology or post-osteotomy deformities, the software facilitated the design of custom implants. Despite a 15-minute planning duration and an average radiation dose of 6.16 mSv, the method eliminates the need for additional specialized radiographic views and improves the predictability of the surgical reconstruction.

Conclusion: CT-based preoperative planning enhances surgical precision by providing a comprehensive three-dimensional anatomical analysis, effectively reducing errors in limb length and femoral offset. It remains a valuable tool for managing complex hip pathologies and optimizing implant selection.