Stiffness and Strength Predictions From Finite Element Models of the Knee are Associated with Lower-Limb Fractures After Spinal Cord Injury

Spinal cord injury (SCI) is associated with bone fragility and fractures around the knee. The purpose of this investigation was to validate a computed tomography (CT) based finite element (FE) model of the proximal tibia and distal femur under biaxial loading, and to retrospectively quantify the relationship between model predictions and fracture incidence. Twenty-six cadaveric tibiae and femora ( n = 13 each) were loaded to 300 N of compression, then internally rotated until failure. FE predictions of torsional stiffness ( K ) and strength ( T ult ) explained 74% ( n = 26) and 93% ( n = 7) of the variation in experimental measurements, respectively. Univariate analysis and logistic regression were subsequently used to determine if FE predictions and radiographic measurements from CT and dual energy X-ray absorptiometry (DXA) were associated with prevalent lower-limb fracture in 50 individuals with SCI ( n = 14 fractures). FE and CT measures, but not DXA, were lower in individuals with fracture. FE predictions of T ult at the tibia demonstrated the highest odds ratio (4.98; p = 0.006) and receiver operating characteristic (0.84; p = 0.008) but did not significantly outperform other metrics. In conclusion, CT-based FE model predictions were associated with prevalent fracture risk after SCI; this technique could be a powerful tool in future clinical research.