Muhammad Hazli Mazlan et al., International Journal of Emerging Trends in Engineering Research, 8(1.2), 2020, 221– 226 221 ABSTRACT Posterior lumbar interbody fusion (PLIF) related complications such as cage instability, cage subsidence and pedicle screws loosening are among the most prevalent cases reported postoperatively. These conditions are highly related to mechanical factors (PLIF design and material), patient health condition as well as activities conducted by the patient after undergone the surgery. Latest advancement on PLIF technology has created a new technique that allows the application of unilateral cage insertion in an oblique orientation. This solution has potentially overcome the problem related to an unintended mechanical and clinical shortcoming, provided that a bilateral posterior instrumentation (PI) is instrumented to the construct and the cage is fabricated from a material that is closely imitate the modulus elasticity of the cortical bone. In order to prove these statements, an image based finite element analysis (FEA) was conducted to assess the phenomena of cage subsidence and screw loosening by examining the stress profile on the cage construct and the vertebral bodies. Obliquely-placed unilateral PLIF with PI showed the most promising results. It showed the most minimal stress distortion at cage-endplate and pedicle screw-bone interface. In conclusion, the selection of a biocompatible cage material is the most crucial factors that has to be considered in achieving biomechanical superiority in PLIF surgery. Key words: Drucker-Prager Stress, Finite Element Analysis, Posterior Instrumentation, Posterior Lumbar Interbody Fusion, Spine. 1. INTRODUCTION The primary function of the posterior lumbar interbody fusion (PLIF) with assistive posterior instrumentation (PI) is to improve structural stability of the motion segment, to assist fusion and to eliminate severe back pain [1]. This surgical procedure is adopted when severe degenerative disc disease with disc space collapse is identified. Other conditions that may also require spinal fusion includes spinal disc herniation, vertebral fracture, scoliosis, spondylosis, kyphosis and any condition that causes instability of the spine. This treatment has been widely accepted as 80,000 interbody fusions were successfully implanted in the year of 1995 to 1999 [2]. Cage is initially fabricated from either medical grade titanium alloy or stainless steel. Latest advancement in medical research has discovered a new medical grade polyetheretherketone (PEEK) material. This material shows better radiolucency if compared to the preceding materials that improves the visibility thus improving the accuracy to locate the cage on the targeted areas. In addition, it is also more compatible to bone as the stiffness of the material (E = 3.6 GPa) is nearer to that of cortical bone (E = 12 GPa). This feature can significantly reduce the stress shielding effect that is associated to titanium alloy (E = 110 GPa) [3]. As the research in medical expanding, carbon fiber reinforced polymers (CF-P) has been introduced to improve the quality of PEEK material. This material has shown high fusion rates and satisfactory clinical outcomes. However, the stiffness factor has undermined the performance of this material over PEEK material that shows PEEK can significantly lessen the risks of cage subsidence into the vertebral body [4]. The majority of the previous studies [5]–[7] has confirmed that PEEK cages could significantly improve fusion rates (93-100% in 12 months’ time postoperatively), reduce subsidence rates on cage-endplate interfaces (0-14.2%) and exhibit excellent clinical outcomes (80-96%). The used of bilateral cage with PI has shown to be the perfect method to achieve high segmental stability. However, this condition is riskier and costly. On these regards, a single Biomechanical Evaluation of two different types of Interbody Cages in Posterior Lumbar Interbody Fusion Muhammad Hazli Mazlan 1,2 , Mitsugu Todo 3 , Ida Laila ahmad 1,2 , Hiromitsu Takano 4 , Ikuho Yonezawa 4 ,Abdul Halim Abdullah 5 , Muhammad Hilmi Jalil 6 and Nur Dalilah Diyana Nordin 7 1 Microelectronics and Nanotechnolgy-Shamsuddin Research Center, Universiti Tun Hussein Onn Malaysia, 86400 Parit Raja, Batu Pahat, Malaysia, mhazli@uthm.edu.my 2 Faculty of Electrical and Electronic Engineering, Universiti Tun Hussein Onn, Malaysia, 86400 Parit Raja, Batu Pahat, Malaysia. 3 Research Institute of Applied Mechanics, Kyushu University, Japan 4 Department of Orthopedic Surgery, Juntendo University, Japan 5 Department of Mechanical Engineering, Universiti Teknologi Mara, Malaysia 6 Department of Mechanical Engineering, Universiti Malaysia Pahang, Malaysia 7 Center of Information Technology, Universiti Tun Hussein Onn, 86400 Parit Raja, Batu Pahat, Malaysia ISSN 2347 - 3983 Volume 8. No. 1.2, 2020 International Journal of Emerging Trends in Engineering Research Available Online at http://www.warse.org/IJETER/static/pdf/file/ijeter3181.22020.pdf https://doi.org/10.30534/ijeter/2020/3181.22020