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

IIntroduction: 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 decade Oblique Lumbar Interbody Fusion (OLIF) have become globally accepted, as a minimally invasive surgical technique. There are several stabilization options available for OLIF cage fixation such as: Self-Anchored Standalone (SSA), Lateral Plate-Screw (LPS), and Bilateral Pedicle Screw (BPS) systems. The constructs’ stability is crucial for the immediate and long-term success of the surgery. The aim of this study is to investigate the biomechanical effect of the aforementioned constructs using finite element analysis, with different bone qualities (osteoporotic, normal). Method: A bi-segmental (L2-L4) finite element (FE) model 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 L3-L4 motion segment during a virtual surgery. For the simulations, 150 N follower load was applied on the constructs, then 10 Nm of torque was used in 6 general directions (flexion, extension, right/left bending, right/left rotation), with different bone-material properties. Results: The smallest segmental (L3-L4) ROMs (Range of Motion) were observed in the BPS system, except for right bending. Osteoporosis increased ROMs in all constructs, especially in LPS (right bend increase: 140.26%) Osteoporosis also increased the caudal displacement of the implanted cage in all models (healthy bone: 0.06 mm±0.03 mm, osteoporosis: 0.106 mm±0.07 mm), particularly with right bending, where the displacement doubled in SSA, and LPS constructs. The displacement of the screws inside the L4 vertebra were increased 59% in average (59.33% ± 21.53%) by osteoporosis (100% in LPS, rotation). BPS-L4 screw displacements were the least affected by osteoporosis. Conclusions: The investigated constructs provide different level of stability to the spine depending on the quality of the bone, which can affect the outcome of the surgery. In our model, the BPS system was found to be the most stable construct in osteoporosis. The presented model, after further development has the potential to help the surgeon in planning, by adjusting the stabilisation type to the patient bone quality.