Influences of Newly Formed Woven Bone on Tissue Stresses in Rat Caudal Vertebrae Subjected to Mechanical Loading: A Study Based on Morphological Measurement Using a Micro-CT and Computational Stress Analysis

Bone tissue stresses in mechanically loaded vertebrae were computationally investigated in order to reveal the influences of adaptive remodeling/modeling on stress distribution. Morphological alteration of the rat fifth caudal vertebrae was periodically and non-invasively measured with a microcomputed tomography (micro-CT). Von Mises stresses were calculated by using a finite element analysis (FEA) together with rigid-body spring models based on the consecutive micro-CT images. Median cross-sectional area periodically increased in the loaded rats depending on the duration of stimuli, which was caused by periosteal woven bone formation. FEA including the newly formed bone demonstrated that the loaded vertebrae showed the lower stress levels compared with non-loaded one. Averaged stress of the offset-loaded rat was markedly symmetry between ventral and dorsal sides under offset loading condition, while that of the non-loaded rat indicated asymmetry. Stress analyses suggested that the loaded vertebrae would adapt to the daily mechanical loading by depositing and calcifying woven bone over periosteum.