Quantification of Internal Disc Strain Under Dynamic Loading Via High-Frequency Ultrasound.

Abstract

Measurement of internal intervertebral disc strain is paramount for understanding the underlying mechanisms of injury and validating computational models. Although advancements in noninvasive imaging and image processing have made it possible to quantify strain, they often rely on visual markers that alter tissue mechanics and are limited to static testing that is not reflective of physiologic loading conditions. The purpose of this study was to integrate high-frequency ultrasound and texture correlation to quantify disc strain during dynamic loading. We acquired ultrasound images of the posterior side of bovine discs in the transverse plane throughout 0-0.5 mm of assigned axial compression at 0.3-0.5 Hz. Internal Green-Lagrangian strains were quantified across time using direct deformation estimation (DDE), a texture correlation method. Median principal strain at maximal compression was 0.038±0.011 for E1 and -0.042±0.012 for E2. Strain distributions were heterogeneous throughout the discs, with higher strains noted near the disc endplates. This methodological report shows that high-frequency ultrasound can be a valuable tool for quantification of disc strain under dynamic loading conditions. Further work will be needed to determine if diseased or damaged discs reveal similar strain patterns, opening the possibility of clinical use in patients with disc disease.