A Clearer Picture of Musculoskeletal Disorders of the Knee and Thumb Through the Lens of Image-Based Finite Element Analysis

Abstract

The first goal of this work was to understand the contributions of intra-cyst fluid pressure to the growth of subchondral bone cysts (SBCs). The equine stifle joint provides a natural animal model for studying SBCs. Finite element models were used to examine three cyst sizes of approximately 0.03 cm3 (C1), 0.5 cm3 (C2), and 1 cm3 (C3) in the equine stifle joint. Fluid pressure was simulated by using a soft solid filling or empty-cysts with uniform pressure loads. The models suggest that shear stresses due to joint loading, not pressurized fluid, are likely the cause of damage to the subchondral bone. The second goal of this work was to develop a modular MRI-compatible micropipette simulator that could be used for MRI-based FEA of the basilar thumb joint. A modular MRI-compatible micropipette simulator addresses several limitations of pipetting studies, and it can be used to isolate micropipette design features to understand how they affect basilar thumb joint contact mechanics. A micropipette simulator with a cylindrical handle (length 127 mm, diameter 25 mm) was used with one subject to demonstrate the system’s feasibility. Contact area, pressure, and location were similar to previously published data of basilar thumb joint models in power grasp and lateral pinch. The simulator’s modularity will allow future studies to examine handle design parameters such as handle diameter, cross-sectional shape, and other features. The third goal of this work was to utilize the modular MRI-compatible micropipette simulator to analyze the effects of three handle diameters (12 mm, 25 mm, and 40 mm) and finger rest inclusion on basilar thumb joint contact mechanics. All contact measures decreased with increasing handle diameter. Contact area and force were higher with a finger rest. We expected contact measures to decrease with the presence of a finger rest. The unexpected outcome may have been due to non-randomized test order and fatigue during testing.