Varying Cortical Involvement of Periacetabular Metastatic Lesions Affects Bone Strain in the Pelvis

Background Metastatic bone disease, common in advanced cancer, significantly impacts survival and quality of life. As cancer survivorship improves, the incidence of skeletal metastases rises. Effective orthopedic constructs are crucial for enhancing patient outcomes. Currently, there is no validated method for biomechanical modeling or optimal surgical treatment of metastatic acetabular defects. Tumors near the acetabulum can weaken the pelvis, but the effect of different defects on fracture risk is unclear. This study aims to develop anatomic models of metastatic pelvic defects to predict fracture risk zones using finite element analysis.

Methods A short fiber-filled epoxy artificial bone was laser-scanned to create a 3D hemipelvic model, including cortical and trabecular regions. Lesions were defined by their cortical bone intersection area, based on binary subtraction. An orthopedic surgeon determined average lesion size and location, following the modified Harrington Classification System. Acetabular defect models were converted into finite element models via volumetric meshing. Analysis compared defect models' volumetric size, cortical bone loss, and stress/strain magnitudes. Peak stresses were evaluated at the medial wall, superior acetabular dome, acetabular rim, anterior, and posterior columns. Margin of safety quantified fracture risk, mapping weakened acetabular areas.

Results Simulated tumors' average length and cortical bone loss were 6.3 cm and 5.5 cm3, respectively. The hemipelvis with the anterior column defect had the lowest margin of safety and highest change in peak stress compared to no defect. The anterior defect and the anterior defect involving the medial wall had similar margin of safety results.

Conclusion Anterior column and anterior column with medial wall defects were more severe than defects involving posterior & medial wall of the hemipelvis, posing greater fracture risks than posterior and medial wall defects. This study enhances our understanding of fracture risk in metastatic pelvic lesions, guiding surgical decision-making and improving patient care by decreasing unnecessary procedures.