While the human vertebra experiences natural degeneration processes, it also encounters many pathological conditions and traumas. In order to handle all these natural and pathological processes correctly, the principles of vertebral biomechanics should be known and adapted to clinical practice. While performing biomechanical tests, the functional spinal unit (FSU), which is the smallest unit of the vertebra, should be evaluated by excluding muscle tissue. Spinal stability and instability are emphasized in the evaluation of vertebral biomechanics in the clinic. Vertebral stability is essential for preserving neural structures and preventing premature mechanical deterioration of the vertebrae. Vertebral biomechanics is an important discipline of spinal surgery with both its physical and clinical aspects. While thoracic and lumbar vertebral fractures cause a sudden change in quality of life, they also cause chronic complications along with pain and functional losses. Vertebral injuries affect a complex structure of soft tissues and bone structures with different traumatic susceptibility and healing potential. This complexity makes it difficult to classify, assess instability and treatment outcomes. However, unlike degenerative instability, there is a more direct relationship between traumatic instability, imaging findings, and clinical symptoms.

Denis`s three columns in thoracolumbar traumas and Kostuik`s modification can be applied in the evaluation of stability due to tumors. Whether we use the column system or the scoring system in the evaluation of spinal stability, we gain the ability to make decisions in a more systematic and rational way in the light of biomechanical concepts.