Abstract:
This study validates a noninvasive image-based technique called Hyperelastic Warping for accurately measuring the three-dimensional strain and deformation distributions within the knee meniscus. The method utilizes finite element (FE) analysis to calculate the deformation required to "warp" a template MR image (unloaded state) into alignment with a target MR image (loaded state), from which a detailed strain map is generated. A hyperelastic constitutive model is used to ensure a physically realistic transformation. To validate the technique, a "forward" FE model of a cadaveric knee was created, with the meniscus represented by a transversely hyperelastic material model. A known compressive load was applied to this model to generate a ground-truth deformation and strain field. This known deformation was used to create a synthetic target MR image from the original unloaded image. The Warping algorithm was then used to predict the deformation between the original and synthetic images, showing excellent correlation with the known ground-truth for both displacement (R²=0.98) and circumferential fiber stretch (R²=0.93). A sensitivity analysis demonstrated that the Warping predictions were relatively insensitive to the assumed material properties of the meniscus. When applied to actual experimental images, the method produced strain patterns consistent with previous studies, confirming its potential as a powerful tool for noninvasive biomechanical analysis of the meniscus in vivo and in vitro.
