Development and experimental validation of a three-dimensional finite element model of the human scapula

Abstract

A new modelling approach, using a combination of shell and solid elements, has been adopted to develop a realistic three-dimensional finite element (FE) model of the human scapula. Shell elements were used to represent a part of the compact bone layer (i.e. the outer cortical layer) and the very thin and rather flat part of the scapula--infraspinous fossa and supraspinous fossa respectively. Solid elements were used to model the remaining part of the compact bone and the trabecular bone. The FE model results in proper element shapes without distortion. The geometry, material properties and thickness were taken from quantitative computed tomography (CT) data. A thorough experimental set-up for strain gauge measurement on a fresh bone serves as a reference to assess the accuracy of FE predictions. A fresh cadaveric scapula with 18 strain gauges fixed at various locations and orientations was loaded in a mechanical testing machine and supported at three locations by linkage mechanisms interconnected by ball joints. This new experimental set-up was developed to impose bending and deflection of the scapula in all directions unambiguously, in response to applied loads at various locations. The measured strains (experimental) were compared to numerical (FE) strains, corresponding to several load cases, to validate the proposed FE modelling approach. Linear regression analysis was used to assess the accuracy of the results. The percentage error in the regression slope varies between 9 and 23 per cent. It appears, as a whole, that the two variables (measured and calculated strains) strongly depend on each other with a confidence level of more than 95 per cent. Considering the complicated testing procedure on a fresh sample of scapula, the high correlation coefficients (0.89-0.97), the low standard errors (29-105 micro epsilon) and percentage errors in the regression slope, as compared to other studies, strongly suggest that the strains calculated by the FE model can be used as a valid predictor of the actual measured strain. The model is therefore an alternative to a rigorous three-dimensional model based on solid elements only, which might often be too expensive in terms of computing time.

An accurate estimation of bone density improves the accuracy of subject-specific finite element models

“…6) that could be particularly important when models are used to estimate bone failure behaviour and may improve model sensitivity and specificity. A peak error of 42% represents an improvement with respect to previously published works (Gupta et al, 2004;Keyak et al, 1993;Taddei et al, 2007) but may still seem large. However, this high discrepancy between predicted and measured strains is limited to a few specific locations and is probably due to the impossibility for FE models based on clinical CT data to capture small surface features or discontinuities (e.g.…”

“…to calibrate HU numbers to r ash with a phantom (or a bone mineral equivalent substance) and then use another relationship to obtain r app (Barker et al, 2005;Dalstra et al, 1995;Keyak et al, 1998Keyak et al, , 2005, or to directly calibrate HU numbers to apparent density. As to the latter case, some studies (Bitsakos et al, 2005;Cody et al, 1999;Gupta et al, 2004;Peng et al, 2006;Taddei et al, 2004) implemented a direct correlation of r app values with HU values, based on the a-priori assumption of at least two HU/r app correspondences (e.g. r app ¼ 0 for HU ¼ 0 and r app ¼ (max estimated cortical density) for HU ¼ (max HU in the dataset)); some other studies do not report sufficient details to replicate the methods used to directly extract r app information from the HU numbers (Gupta et al, 2006;Vazquez et al, 2003;Wagner et al, 2002;Wong et al, 2005).…”

Experimental validation of numerically predicted strain and micromotion in intact and implanted composite hemi-pelvises

“…However, biomechanical investigations into phenomena such as the load transfer mechanism across the pelvis and the acetabular reconstruction remain relatively under-investigated as compared to the femoral component. Measurement of such phenomena across the intact and implanted bones would be a useful step forward in the analysis of acetabular failure, and to date this has commonly been evaluated using finite element (FE) analysis [5][6][7][8][9][10][11]. The validity of the FE model generation process should be assessed using quantitative comparisons between computational predictions and experimental results [Anderson et al, 2007].…”

Comparison of beam theory and finite‐element analysis with in vivo bone strain data from the alligator cranium

“…However, these are typically conducted using either skeletal elements with a relatively simple geometric structure (Gross et al, 1997(Gross et al, , 2002Kotha et al, 2004) or in vitro strain data (Gupta et al, 2004). This study represents one of the first validation studies of a geometrically complex skeletal structure using in vivo data collected under naturalistic conditions (Strait et al, 2003.…”