Abstract
Subject-specific finite element models (FEMs) of the shoulder can be used to evaluate joint replacement designs preclinically. However, to ensure accurate conclusions are drawn, experimental validation is critical. The objective of the current study was to evaluate the accuracy of strain predictions generated by subject-specific scapula FEMs through comparisons against full-field experimental strains measured using digital volume correlation (DVC). Three cadaveric scapulae were mechanically loaded using a custom-hexapod robot within a micro-CT scanner. BoneDVC was used to quantify resultant experimental full-field strains. Scapula FEMs were generated using three different density-modulus relationships to assign material properties. Two types of boundary conditions (BCs) were simulated: DVC-displacement-driven or applied-force-driven. Third principal strains were compared between the DVC measurements and FEM predictions. With applied-force BCs, poor agreement was observed between the predicted and measured strains (slope range: 0.16–0.19, r2 range: 0.04–0.30). Agreement was improved with the use of DVC-displacement BCs (slope range: 0.54–0.59, r2 range: 0.73–0.75). Strain predictions were independent of the density-modulus relationship used for DVC-displacement BCs, but differences were observed in the correlation coefficient and intercept for applied-force BCs. Overall, this study utilized full-field DVC-derived experimental strains for comparison with FEM predicted strains in models with varying material properties and BCs. It was found that fair agreement can be achieved in localized strain measurements between DVC measurements and FEM predictions when DVC-displacement BCs are used. However, performance suffered with use of applied-force BCs.
Highlights
Subject-specific finite element models (FEM) of the shoulder offer the capability to evaluate the performance of joint replacement designs prior to clinical adoption (Geraldes et al, 2017)
Highest errors associated with strain predictions of the FEM were found within the regions of interest (ROI) closest to the loading platen and this was consistent for all FEMs (Figure 6)
Within this ROI, higher errors were observed with the use of applied-force BCs
Summary
Subject-specific finite element models (FEM) of the shoulder offer the capability to evaluate the performance of joint replacement designs prior to clinical adoption (Geraldes et al, 2017). As these models can isolate and alter design variables in a cost-effective and parametric fashion, they offer distinct advantages over experimental bench-top testing. For strain-based outcomes, the assignment of material properties using density-modulus relationships and simulated boundary conditions are cited sources of variability (Helgason et al, 2016; Hussein et al, 2018). In-vitro biomechanical testing has previously been conducted to assess the accuracy of subject-specific shoulder FEMs in predicting strain-based outcomes (Dahan et al, 2019, 2016)
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