Finite Element Analysis of Superior C3 Cervical Vertebra Endplate and Cancellous Core under Static Loads

Subsidence is a type of failure associated with implanted cervical cages or artificial intervertebral discs. It is defined as a loss of postoperative disc height. Actuarial rates show a risk of subsidence at 16 weeks at 70.7 percent. This study examines the changes in the vertebral endplate morphology and the resulting effect on the stresses developed in the endplate and in the vertebral core. A three-dimensional linear elastic model was created from computed tomographic (CT) scans and material properties were assigned according to various studies. Particular care was taken in the superior endplate that was modeled according to experimental measurements. Von Mises stress values were examined in the vertebral endplates and the cancellous core. The stresses were the result of a static load analysis. The stresses analyzed comparing a model with an idealized half-millimeter endplate to anthropometrically based models see if the half-millimeter thick endplate is an adequate approximation. The stresses in the cancellous core were measured at various levels to see how stress propagated through the core with the adjustment of the endplate. The core stresses were investigated to identify regions of potential failure. Ideally this information would be used to improve intervertebral device design.