Biomechanics of soft tissues in the shoulder joint-glenohumeral cartilage, ligament, and rotator cuff tendon

This study develops a better understanding of the biomechanics of glenohumeral (GH) cartilage, inferior glenohumeral ligament (IGHL), and supraspinatus tendon, which are associated with the clinical problems of the shoulder joint such as osteoarthritis, shoulder instability, and rotator cuff failure. Firstly, this study provides a systematic and extensive assessment of complexity of the tensile and compressive properties of GH cartilage, showing their anisotropy, inhomogeneity, and tension-compression nonlinearity. Furthermore, a theoretical model is proposed to simultaneously account for the tension-compression nonlinearity and intrinsic viscoelasticity of cartilage, and verified against experimental data of static and dynamic compression tests. Secondly, the viscoelastic responses of the three anatomical regions of the IGHL under cyclical loading are modeled using the quasi-linear viscoelasticity (QLV) theory to better understand their functional roles of stabilizing the glenohumeral joint. Finally, the inhomogeneous deformational characteristics of the supraspinatus tendon are investigated by determining the inhomogeneous (articular versus bursal tendon surface) strain fields at three arm elevations using a multiple strain measurement system. In addition, the temperature effects on the intrinsic viscoelastic properties of the supraspinatus tendon is also investigated by analyzing the experimental results of the tensile stress-relaxation tests using the QLV theory.