Biomechanical Study of Fused Lumbar Spine Considering Bone Degeneracy Using FEA

Abstract

Pedicle screw fixation is a universally accepted technique in the surgical treatment of spinal disorder. The existence of high mechanical stresses on the vertebral body due to loading/bone degeneracy on patients having vertebral implants may result in malfunctioning of the pedicle screws. The present work aims to predict the effect of various pedicle screws used in vertebral implants considering bone degeneracy and to select the screw for improved performance. A three-dimensional (3D) intact and fused model of L2–L3–L4 is generated for biomechanical and FE study. To consider degeneracy, bones were categorized into four groups, i.e., weak bone, normal bone, strong bone and very strong bone. The developed FE model was subjected to various axial compressive loads (270, 330, 450 and 510 N), and pure moment of 10 Nm is applied at the top surface of the L2 vertebra, while the lower surface of the L4 vertebra remains fixed. Three different diameters of the pedicle screw (5.5, 6.0 and 6.5) were considered to identify localized stress generation at bone–screw interface. Results prevail that pedicle screw of 6.0 mm diameter, 45 mm length enables minimum stress distribution at the bone–screw interface considering flexion, extension, bending and twist. The observations and data shown in the results may support researchers and clinical practitioners to identify accurate pedicle screw for vertebral implants so as to minimize screw failure/loosening. The work may help to design new vertebral implants and to identify the after-effects of implantation with varying bone densities.