Finite element model validation based on an experimental model of the intact shoulder joint

The shoulder joint is a complex anatomical system. The main goal of this study was to build a Finite Element (FE) model of the intact shoulder joint and its validation was done using an experimental model comparing cortical strains. Considering the expected differences between the experimental model and an in vivo shoulder, the experimental model developed replicates adequately the in vivo functioning of the joint. For the experimental model we used 4th generation composite bone structures of the humerus and scapula, including the humeral head cartilage, the glenoid cartilage and glenohumeral ligaments. The model also comprises the most important muscles in abduction. The FE model of the intact shoulder was developed mimicking the experimental model regarding the geometry of the bone structures. Strain gage rosettes were used to measure strain responses loading bone structures positioned in a 90° abduction angle. The accuracy of the strains calculated (numerical model) and measured (experimental model) was evaluated with linear regression analysis. The correlation coefficient of 0.76 and RMSE of 107 µε indicate an adequate agreement between numerical and experimental strains. The experimental procedure to simulate the biomechanics of the intact shoulder joint is a difficult task due to the instability of the joint and the number of structures that compose it. The use of FE models is necessary to perform more complex biomechanical studies, which are normally impossible to make with experimental ones, highlighting the importance of validation of FE models. The results of these models can then be used to compare with clinical data considering, however, the inherent characteristics of numerical simulations and differences relatively to clinical models.