Computational Investigation for Biomechanical Characteristics of Lumbar Spine with Various Porous Ti–6Al–4V Implant Systems

(1) Background: Metallic materials are predominantly used for spinal implants, and they can damage adjacent bones and intervertebral discs (IVDs) owing to their high elastic moduli. Consequently, there is a possibility that serious complications, such as kyphosis, may occur as the sequelae progresses. In this study, the behavior of the lumbar spine and implant system was evaluated using the finite element (FE) method, by applying the porous structure to the spinal implants to resolve the problem of metal spinal implants. (2) Methods: An FE model was developed for lumbar 3–5, and it was assumed that, owing to disease occurrence, spinal implants were placed in lumbar 3–4. Currently, Ti–6Al–4V is the most commonly used material for spinal implants. The shape of the porous structure was set in the form of a diamond, and porosity was varied over nine values ranging from 0 to 81%. Finally, equivalent material properties of the porous structure were derived using the Ramberg–Osgood formula, with reference to experimental study. (3) Results: The range of motion was increased, and the equivalent stress of adjacent IVD, and adjacent bone stress of the pedicle screw and spinal cage, decreased with increasing porosity of the spinal implants. As the porosity decreased, the safety factor exhibited a tendency to decrease rapidly. (4) Conclusion: Motor capacity of the spine was improved, and the equivalent stress of the spinal tissues decreased with the increasing porosity of the spinal implants. Therefore, in the future, porous structures can significantly contribute to the improvement of implants through continuous complementary research.