Biomechanical analysis of atlantoaxial dorsal fixation using finite element models

Abstract

Atlantoaxial instability can cause spinal cord compression with clinical signs ranging from cervical pain to tetraplegia and death. Although a variety of dorsal fixation techniques have been described, some of them have been related to the fracture of the dorsal arch of the atlas, leading to surgical failure. Under the hypothesis that the shape of the dorsal arch of the atlas and types of implants might affect these bone fractures, the objective of this study was to analyze bone stresses through simulations of the dorsal fixation using finite element models. Arbitrary tension forces were given to implants for simulations of the dorsal fixation and the maximum von Mises stress of the bone was analyzed. The maximum bone stress increased as the bone got thinner and the angle of the notch got steeper. The width between wires and the length of the bone did not affect the maximum stress on the bone. Bone with band implant had lower maximum bone stress than that with wire implants. When using wire implants, wires applied beyond the notch of the dorsal arch reduced the maximum bone stress more than wires positioned within it. Therefore, the fracture of the dorsal arch of the atlas was related to the shape of the bone and types of implant applied. Band implant can effectively reduce fracture of the dorsal arch compared to wire implant in atlantoaxial dorsal fixation. When considering wire implant, it is recommended to apply wires beyond the notch of the atlas.