PhD Scientific Days 2021

CL_VII_L: Clinical Medicine VII. Lectures

Stability Evaluation of Different Oblique Lumbar Interbody Fusion Constructs in Normal and Osteoporotic Condition –a Finite Element Based Study

Text of the abstract

Introduction: In developed countries the age structure of the population is currently undergoing an upward shift resulting in a decrease of general bone quality and surgical durability. Over the past 15 years Oblique Lumbar Interbody Fusion (OLIF) have become globally accepted, and used as a minimally invasive surgical technique. There are several implants avaible for fusion such as: Self-Anchored Standalone (SSA) Lateral Plate-Screw (LPS) Bilateral Pedicle-Screw (BPS) systems. The implant’s rigidity, general movements, and the biomechanical effect on bones are crucial for the long-term success of the surgery.

Aims: The aim of this study is to investigate the biomechanical effect of the aforementioned implants using finite element analysis, under different bone qualities (osteoporotic, normal).

Methods: A finite element (FE) model consisting of two lumbar motion-segments (LII-IV) was created using a CT scan of a 24-year-old healthy male. After the FE model validation, CAD geometries of the implants were inserted into the LIII-IV motion segment during a virtual surgery. During the simulations a 150 N vertical preload was applied on the constructions, then 10 Nm of torque was used according to the 6 general movement directions (flexion, extension, right/left tilt, right/left rotation), with the 2 different bone material qualities.

Result: The smallest displacements were observed in the BPS system, except for right bending in the FE models regardless of bone quality. (intact model: 4,45o ± 1,58o normal bone /BPS/: 0,37o ± 0,11o, osteoporotic bone /BPS/: 0,49o ± 0,15o). Osteoporosis increased the caudal displacement of the implanted spacer in all three models (physiological bone: 0.06 mm ± 0.03 mm, osteoporotic bone: 0.106 mm ± 0.07 mm), especially with right bending, where the displacement doubled in SSA, and LPS constructs. In the osteoporotic material model, the displacement of the screws inside the caudal (LIV) vertebra were increased on average by 59% (159.33% ± 21.53%) compared to physiological bone models.

Conclusion: When planning a particular spinal surgery, the surgeon must consider several aspects. Different fixation systems provide different stability to the spine depending on the quality of the bone, which affects the effectiveness of bony fusion. In silico biomechanical models can help the surgeon in this choice.

Funding: OTKA FK123884

University and Doctoral School

Semmelweis University, Károly Rácz Doctoral School of Clinical Medicine