Biomechanical Study of Simulated Metastatic Peri-Acetabular Defects

Peri-acetabular metastasis presents the risk of fracture. However, the relationship between bone loss and fracture risk is unknown. Utilizing fresh frozen intact cadaver pelves, Harrington class I lesions were simulated. Lesions were categorized as small ( 40%) Axial loading was applied in a quasistatic mechanism by a mechanical testing system to catastrophic failure, with the load-to-failure force being measured. There was statistical difference in the load-to-failure force between hemi-pelves with large defects and their matched controls. It was found that mean load-to-failure strength of a hemi-pelvis with a Class I defect was more than 2.3-2.45 times the calculated hip joint reactive force. Thus, it was concluded that a pelvis with a peri-acetabular defect of greater than 40% has a significantly lower load-to-failure strength compared to an intact pelvis. However, even this large Class I defect will fracture only at supraphysiologic loads and the hip joint may not normally be exposed to forces that high.