We used the finite element method (FEM) to investigate the stress profiles of vertebrae\nin patients who underwent balloon kyphoplasty (BKP) for vertebral fracture.\nBKP is often performed for persistent pain after vertebral fractures. However, fractures\nare frequently reported in the adjacent vertebrae after BKP. The purpose was to\nclarify the mechanism of fractures that occur in the adjacent vertebrae after BKP.\nThe subjects were two patients (first case: 74-year-old woman; second case: 88-yearold\nwoman) who had BKP for osteoporotic vertebral fractures (L1). A bone analysis\nsoftware program, Mechanical Finder, was used to construct three-dimensional finite\nelement models (T11-L3) from computed tomographic (CT) digital imaging and\ncommunications in medicine (DICOM) data. Moment loadings were examined to\nevaluate stress concentrations on the vertebrae. Young�s moduli were lower in the\nsecond case than in the first case at all vertebral levels. Maximum Drucker-Prager\nstresses after BKP were larger in the second case than in the first case for compression,\nflexion, extension, and axial rotation. Strain energy density decreased in L1 and\nincreased in the adjacent vertebrae. Our results suggest that post-BKP fractures of\nthe adjacent vertebrae not only are due to bone fragility, but also can be caused by\nincreased rigidity in the vertebrae filled with bone cement, which increases stress\nconcentration on the adjacent vertebrae and raises the likelihood of fracture.
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