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Fig 1. Intact (A) and fractured (B) FEMs of a hemisacrum are shown, which were constructed by using densitometric CT data from a single imaged cadaveric pelvis. In the models (A, B), a system of individual elements interconnected by a meshwork of discrete nodes has been assigned elasticity parameters approximating that of bone. Boundary and loading conditions applied to the intact sacral fracture and cement-augmented sacral fracture models are demonstrated (A). Hatch marks (A) represent boundary conditions that were applied to simulate anchoring of the sacrum at the sacroiliac joint. Yellow vector lines (A) indicate loading conditions, which were defined as a 35-kg force, approximating one half of body weight above the first sacral vertebra. Arrowheads (A) demonstrate the sagittal plane along which movement could occur in a 1-legged-stance paradigm. An asterisk and solid arrow (B) indicate sacral fracture origin and the point of fracture propagation, respectively. Color-coded transformation of FEA data demonstrates the amount of maximal principal stress experienced by the hemisacrum after the application of a 35-kg load, both before (C) and after (D) fusion at a point along the fracture (open arrow) designed to simulate sacroplasty. Each color represents kilopascals of maximal principal stress according to the calibration scale provided (E), with red corresponding to the lowest and white corresponding to the highest levels of maximal principal stress. Note that the point of fracture fusion (open arrow, D) appears to subsume a portion of the stress generated by the 35-kg load, thereby attenuating maximal principal stress that surrounds the site of fracture propagation, as compared with the prefusion model (C).
