Validation of a virtual implantation algorithm to quantify surgeon control and optimize stem selection in total hip...

Area of Science:

• Orthopedic Surgery
• Biomedical Engineering
• Computational Anatomy

Background:

• Accurate restoration of femoral offset (FO) and femoral head center is crucial for optimal joint function in total hip arthroplasty (THA).
• Current templating methods for THA often rely on static, 2D representations, limiting the understanding of achievable 3D stem positions and their impact on joint biomechanics.
• The intraoperative range of achievable femoral stem positions and their effect on femoral head center restoration remains largely unquantified.

Purpose of the Study:

• To develop and validate a fully automated, CT-based virtual implantation algorithm for mapping patient- and implant-specific "feasibility spaces" of achievable postoperative femoral head center locations.
• To identify optimal stem-head configurations that best restore native anatomy within these defined feasibility spaces.
• To quantify the surgical control and anatomical "forgivingness" offered by patient-specific anatomy in THA.

Main Methods:

• Development of a fully automated CT-based virtual implantation algorithm utilizing preoperative CT and postoperative optical scans of cadaveric specimens (16 hips).
• Segmentation of femoral canal boundaries and probabilistic simulation of valid 3D stem alignments across multiple component sizes to generate patient-specific feasibility spaces.
• Validation of the algorithm by comparing experimentally determined stem positions from bilateral THA with a cementless femoral stem against the closest predicted virtual alignments.

Main Results:

• Experimental femoral head centers deviated 12.7 ± 4.8 mm from native targets, with the algorithm predicting these placements within 1.9 ± 0.5 mm.
• Feasibility spaces exhibited a conical distribution, with implanted head centers consistently clustering on the medial boundary.
• For each specimen, at least one stem-head option generated a feasibility space within 5 mm of the native head center, demonstrating the potential for accurate restoration.
• Anterior-posterior controllable ranges (11.2-35.7 mm) significantly exceeded medial-lateral ranges (4.2-14.4 mm), both expanding with superior stem seating.

Conclusions:

• The developed algorithm effectively quantifies the 3D "feasibility space" of achievable femoral head center locations in THA, moving beyond static templating.
• This framework enables systematic risk stratification and objective implant design comparison by quantifying anatomical "forgivingness" and surgical control.
• The findings provide a foundation for minimizing biomechanical errors and enhancing surgical consistency in total hip arthroplasty across diverse patient populations.