Excessive soft tissue loading can produce pathophysiological changes in the absence of tissue failure or visible injury [1]. In these cases, strain has often been used as a metric to infer the location of damage and define tissue tolerances due to a lack of any other means to detect injury. A recent study of the human facet capsular ligament identified localized anomalous collagen fiber realignment prior to gross failure by correlating fiber alignment vectors derived from quantitative polarized light imaging [1]. The onset of anomalous fiber realignment was strongly associated with a decrease in tissue stiffness in that study, suggesting the occurrence of damage, but the location of this putative damage did not correspond to the location of maximum principal strain. The disconnect between maximum strain and the location of damage may be explained by the heterogeneous structural organization of the facet capsular ligament. By employing image-based multiscale computational models, which account for the local fiber alignment of the tissue, we hypothesized that estimates of the tissue stress field may predict the development of microstructural damage that occurs outside of the location of maximum strain. In this study, multi-scale fiber network models were compared to the experimentally-derived strain fields during facet capsular ligament loading up to the detection of anomalous fiber realignment to begin to understand the relationships between macroscopic tissue loading, collagen fiber reorganization, and the development of initial localized microstructural damage.

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