Dr. Ellen Arruda
Chair, Mechanical Engineering.
University of Michigan
Friday, Apr. 3rd at 3:00pm
3550 MEK
ABSTRACT: Partial-thickness rotator cuff tendon tears are a prevalent cause of pain and disability, affecting 13–32% of the general population. Despite the clinical significance, the natural progression of these tears remains poorly understood. Surgical intervention is generally recommended when more than 50% of tendon thickness is involved; a threshold based primarily on anecdotal evidence. Furthermore, retear rates after repair can be as high as 35%, underscoring the need for improved characterization and targeted treatment strategies. To address these gaps, my laboratory has pioneered a soft-tissue characterization approach that integrates full-field kinematic measurement with inverse methods to determine material properties. Building on successful application to soft tissues and elastomers, we have developed a custom displacement-encoded MRI protocol, in which the phase of each voxel (modulo 2π) directly quantifies displacement during tendon stretching. This enables acquisition of the entire three-dimensional displacement field of the rotator cuff tendon at sub-millimeter resolution. We couple these high-resolution imaging data with a novel variational system identification (VSI) method, deployed for the first time on soft tissue. VSI enables systematic inference of the most parsimonious and physically meaningful material models. Applying this approach to both intact and partially torn rotator cuff tendons, we observe distinct differences in shear strain distributions, particularly elevated shear within the interior of partially torn tendons. We emphasize that these features can’t be captured by any other method. Our findings suggest delamination (mode II failure) as a key mechanism in tear progression, with direct implications for surgical strategy and risk of retear.
We further demonstrate that anatomical differences influence strain patterns, strengthening the case for personalized, data-driven approaches such as digital twins. Our vision is that these digital replicas, generated using high-resolution MRI-derived geometries, could inform surgeon decisions regarding tear management and suture placement to minimize retear risk with unprecedented insight into rotator cuff tendon mechanics, and has the potential to improve clinical outcomes through personalized surgical planning.
BIO: Professor Ellen M. Arruda is the Tim Manganello/BorgWarner Department Chair and Maria Comninou [Com Nee New] Collegiate Professor of Mechanical Engineering at the University of Michigan. She also holds appointments in Biomedical Engineering and Macromolecular Science and Engineering. Professor Arruda’s teaching and research focus on the theoretical and experimental mechanics of polymers, elastomers, composites, and soft tissues. Her pioneering work includes experimental characterization and analytical and computational modeling of soft materials, including both native and engineered tissues. Internationally recognized for co-developing the Arruda-Boyce model of hyperelasticity, she has advanced constitutive modeling of soft materials Her research excellence has been recognized with numerous prestigious awards, including the 2023 Borelli Award from the American Society of Biomechanics, the 2021 Eringen Medal from the Society of Engineering Science, the 2019 Nadai Medal from the American Society of Mechanical Engineers, and the 2018 Rice Medal from the Society of Engineering Science. Professor Arruda has published approximately 125 journal papers, holds 16 patents, and her work has been cited over 18,000 times (H-index: 52, Google Scholar).