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Displacement and strain of the spine in the context of asymmetric pelvic bones.

Introduction: Asymmetry within the pelvic structure can lead to a cascade of postural compensations throughout the spine, predisposing people to recurrent somatic dysfunction and decreased functionality. As a basic structural element, the pelvis should be fully symmetric with respect to the sagittal plane. However, many studies conducted by different researchers showed, that an imbalance of the pelvis is very common. This conclusion was recorded based on various measurement types conducted by means of Xrays, CT as well as sectional preparations. Objective: The aim of this research was to discover how the spinal column relates to the sagittal & frontal plane when there is a unilateral tilt of the pelvis in place. The size of strain and displacement were not as significant as the change of shape itself during such altered conditions. The expected results were not found to be particularly complex, thus allowing an extremely simplified model of the human spine to be created. The developed models supporting structure and it’s sustaining stability attributes were assumed to be most important when situated in a vertical position. Methods: In order to provide an analysis of the finite element method, a prototype model was developed replicating the concept of the vertebral body alternate with intervertebral discs shaped in the form of ‘pole like’ tubular sections (Figure 1). The model of the spine, having a physiological curvature, is fixed to the base which, in turn is placed in a mechanism replicating a tilt, relevant to an asymmetric position of the sacrum. Results and Discussion: Simulations conducted in three various tilt positions resulted in the conclusion that strain on the scoliotic-ally deformed vertebral column occurs primarily in the intervertebral discs, whose elastic modulus is considerably lower than of vertebral bodies. It is worth mentioning that the largest accumulation of strain can be observed within the intervertebral discs T6-T7 and L2-L3. One can draw a conclusion that apical curves occur in the most curved regions of the spine, which results in multiplication of strain accumulation throughout these areas. Conclusion and Significance: The greater the tilt of pelvic alignment, the higher the strain rates throughout the intervertebral discs and a larger scale of displacement of the vertebral column resulting in a higher degree of lateral curvature. An asymmetric correlation of the pelvic bones may cause displacement and strain of the vertebral column, thus resulting in pathological changes such as scoliosis. References: [1] Boulay C, Tardieu C, Benaim. Three-dimensional study of pelvic asymmetry on anatomical specimens and its clinical perspectives. Journal Compilation of Anatomical Society of Great Britain and Ireland. 200; 208: 21-33. [2] Debska B, Dluski M. Attempt of assessment of relation between asymmetry of pelvis and shape of scoliosis. Journal of Orthopaedics Trauma Surgery and Related Research. 2013; 32(2): 27-37. [3] Dluski M., Attempt of analysis of child ilium asymmetry in anteroposterior projection based on xray pictures. Przegląd Lekarski. 2007; 64: 28-31.