Stress Analysis in Pedicle Screw and Bone Interface by Various Contact Models in Scoliotic Spine Fixation
Meifal Rusli (a*), Hendery Dahlan (a), Roni Eka Sahputra (b), Mulyadi Bur (a)
a) Mechanical Engineering Department, Faculty of Engineering, Andalas University, Kampus Unand Limau Manis, Padang 25163, Indonesia
* meifal[at]eng.unand.ac.id
b) Orthopedics Department, Faculty of Medicine, Andalas University, Jalan Perintis Kemerdakaan, Sawahan Timur, Padang 25171 – Indonesia
Abstract
Scoliosis is defined as a musculoskeletal condition that has an abnormal lateral spinal curvature as its main feature. One of the medical treatments for scoliotic spine is by surgery to install an instrument or implant consists of pedicle screws, rods, and connector in fixation of the spinal curvature. However, many cases of failure both in the instrument and the interface of bone and pedicle screw connections were found. One of the problems occasionally was related to the risks of screw loosening and pulled out. This paper will observe and discuss numerically the stress distribution in the screws and bone interface in scoliotic spine fixation using finite element analysis. The contact interface is modeled variously by bonded contact, friction contact, and frictionless contact. The analysis is done by two types of load; axial or pull out load and shearing load. It is found that in bonded contact between screws and bone, the stress distribution is more uniforms along the contact surface and lower maximum stress in the bone. Therefore, the risk of pulling out the screws will be minimized. On the other hand, friction contact with a low friction coefficients makes the stress distribution in concentrated in specific region and increase the maximum stress in bone.
Keywords: scoliosis; pedicle screws; stress shielding; pull out; contact model
Topic: Mechanical Engineering