Biomechanical and Computational Modeling of Metastatic Acetabular Defects: Influence of Tumor Location on the Risk of Fracture.

Background: Metastatic bone disease can lead to pathologic fracture of the pelvis which affects quality of life. There are limited validated approaches for biomechanical modeling, classification, or surgical treatment of metastatic acetabular defects. Methods: An artificial hemipelvis bone was used to calibrate a computed tomography-based computational model of the pelvis with varying locations and sizes of acetabular defects. Metastatic defects affecting the anterior and posterior column, medial wall, and their combinations were created. Mechanical testing was performed on each defect, and images of the lateral surface of the acetabulum were analyzed by digital image correlation to measure peak surface strains. Finite element models were calibrated to match the measured peak surface strains. Pelvic stress during acetabular loading was predicted at the (1) medial wall, (2) superior acetabular region, (3) anterior, and (4) posterior columns. Acetabular regions with the highest risk for fracture based on margin of safety were identified by the defect type. Results: = 0.95) with the biomechanical testing results, with a mean error of 0.14 ± 0.12 mε. Combined posterior column and medial wall defects had the highest surface strain and resulted in decreased margins of safety by 66% in the superior acetabular region and 86% in the anterior column. Across all single-region defects, the posterior column defect was the most at-risk for fracture, with a margin of safety reduction of 63% in the medial wall. Conclusions: Pelvic fragility resulting from metastatic lesions was sensitive to the periacetabular defect location. Combined posterior column and medial wall defects caused the greatest compromise to pelvic structural integrity, with the superior acetabular region and medial wall identified as the most critical locations for pelvic fracture. These findings influence surgical decision-making by identifying posterior column and medial wall lesions as high-risk patterns that may require earlier prophylactic stabilization. Level of Evidence: Level V. See Instructions for Authors for a complete description of levels of evidence.