Monday  |  Salon 8  |  01:30 PM–01:50 PM

#15638, Three Dimensional Strain Analysis of Intact and Artificially Torn Ovine Infraspinatus Tendons

Rotator cuff tears are a leading cause of morbidity and economic loss secondary to musculoskeletal injury. These tears most commonly occur at the greater tuberosity enthesis. High-grade partial-thickness injuries that involve greater than 50% of the tendon’s footprint (type III tears) and full-thickness tears are often repaired surgically. While nonoperative treatment is an option, the risk of propagation is poorly understood for various tear types and locations (type I: <25% thickness, type II: <50% thickness), relying on anecdotal evidence for a surgical decision. Surface strain measurement methods have been used to mechanically characterize and predict tear propagation. However, the heterogeneous nature of the supraspinatus tendon and its insertion to the humeral head prevent the identification of intratendinous features or strain concentrations that may arise in the articular surface in the presence of a tear. To further elucidate tear propagation and natural history of progression, we utilized a full-field strain characterization technique in an intact and surgically created supraspinatus tendon tear in an animal model (ovine infraspinatus tendon) subjected to uniaxial tension in the fibers direction. Our samples were cyclically loaded in neutral position (0 degrees abduction and rotation) inside a magnetic resonance imaging chamber, in which a displacement encoding protocol was applied. Three clinically relevant cases were analyzed, intact tendon, and 25% and 50% articular-sided tendon tears with two physiologically relevant target load regimes for each case (90 N and 180 N respectively). The resulting Lagrangian strain maps present a complex three-dimensional distribution of strains with large strain gradients in articular areas close to bone prominent features. The high load regime shows overall increase in strain values, as expected. Maximum principal strain concentration areas close to the attachment are accentuated and rechanneled into regions close to the tear (low load) or the tendon midsubstance (high load) with increasing tear size. This trend is not observed for maximum shear strains. At low load, this behavior could suggest predominance of mode I failure onset. Future work includes testing samples with artificially created bursal-sided tears, samples loaded in the supraphysiological regime, and various full-thickness tear patterns, with the goal of identifying tears at high risk of propagation and defining a threshold for surgical repair.

Carla Nathaly Villacís Núñez   University of Michigan
Ulrich Scheven   University of Michigan
Asheesh Bedi   NorthShore Orthopedic and Spine Institute
Ellen Arruda   University of Michigan