Musculoskeletal modelling of the shoulder complex and its application for EMG assessed pathologies

The aim and purpose of the presented thesis is with regard to musculoskeletal model improvements of the human shoulder and simulation of pathologies. It addresses three distinct research questions. From a modelling perspective using an inverse dynamics approach, there is a discrepancy between computed glenohumeral joint reaction forces and in-vivo measurements above 90° humeral abduction. Invivo measurements and muscle activities derived from electromyographic measurements indicate a continuous increase in the joint reaction force above 90° abduction. Models using an inverse dynamics approach however tend to compute decreasing forces above 90° abduction. In order to address this issue, several modelling parameters are tested and compared with regard to their effect on muscle activation and force development in the glenohumeral joint. Two clinical research questions are addressed and simulated with an updated model. The first investigates several operative techniques of a long biceps tendon transposition from a biomechanical perspective. As multiple techniques are used in the clinical practice, it is of interest how they compare in terms of joint reaction forces and whether one technique provides an outcome which is closer to the healthy state of the shoulder-arm complex. The second simulates tears of the m. supraspinatus and evaluates muscle recruitment changes, changes of the joint reaction forces and a comparison to electromyographic measurements. This is done in order to assess, how model predictions compare to observations in the clinical field and whether a generic model can predict these changes. The major outcomes of this thesis are threefold: it postulates the mechanical muscle properties Hill muscle model as key parameter for the force development in the glenohumeral joint during abduction, argues for an insertion of the long biceps tendon at the bicipital groove as superior operative technique from a biomechanical point of view and depicts a discrepancy between simulated symptomatic cases of a tear of the m. supraspinatus with regard to electromyographic measurements