Shoulder problems such as anterior shoulder dislocation and rotator cuff tears are common shoulder musculoskeletal disorders. However, the cause of many shoulder disorders has not been studied adequately. The objective of this project is to develop and validate a large-scale subject-specific finite element (FE) model of the human shoulder complex to enhance our understanding of the biomechanical mechanism underlying joint motion and solve clinically related problems. It is hypothesised that a comprehensive subject-specific FE model of the human shoulder complex can represent the stability and mobility nature of the joint during normal movement in-vivo. The in-vivo shoulder motion measurement data of a young healthy male subject was collected first using a three-dimensional (3D) motion analysis system and subsequently used to construct a multi-body shoulder musculoskeletal model using OpenSim software to estimate the in-vivo subject-specific muscle activities. Driven by those derived muscle loadings, a subject-specific FE shoulder model with detailed representations of all the major musculoskeletal components was constructed based on high-resolution MR images scanned on the same subject. Quasi-static FE analysis was conducted to simulate the in-vivo subject-specific scapular abduction. Thereafter, the constructed FE model was used to perform a biomechanical study to investigate the effect of the rotator cuff tears on the glenohumeral joint stability during the propagation of the tears. A novel integrative stability index was proposed and used to quantitatively analyse the simulated results. In the quasi-static FE simulation of the scapular abduction of the healthy shoulder, the magnitude of the bone-on-bone forces of the simulation results at joint position 0, 10o, 20o and 30o were found to be 8.18N, 91.45N, 146.14 and 408N, respectively. Whereas, the superior movement of the humeral head centre with respective to the scapula from 0 to 30o was found to be 2.02mm. Both of the bone-on-bone force and humeral head superior movement of the FE simulation results were found to be in very good agreement with previous experimental and computational results in the literature. The biomechanical study simulating the propagation of the tears demonstrated that the stability of the glenohumeral joint decreased from 100% in intact condition to 0.18% in full rotator cuff tear condition. Important clinical findings were summarised as (1) the stability of the glenohumeral joint generally decreases with the increasing tear sizes; (2) smaller sizes of tears do not significantly affect the joint stability, in addition, the critical tear size in which the consequence of the rotator cuff tears becomes severe was determined as tear involved whole supraspinatus tendon and half of the infraspinatus tendon. The obtained results and findings could be used to improve the diagnostic and therapeutic strategies for clinicians when dealing with shoulder disorder patients. To sum up, in this study, a subject-specific finite element model of the human shoulder complex has been constructed and validated, and further used in investigating of the effect of the rotator cuff tears on the glenohumeral joint stability during the propagation of the tears.