The glenohumeral joint has a large range of motion which is needed for everyday activities. As a consequence, the shoulder has less bony stability than other diarthrodial joints and the static restraints must work synchronously with the musculature to maintain joint stability. Despite their important role, little is presently known regarding the forces in the primary static stabilizers, which include the glenohumeral capsule, ligaments, and labrum. As a result, the diagnosis and treatment of glenohumeral joint injuries, understanding of injury mechanisms, and the development of rehabilitation protocols are hindered.

A combined experimental and computational approach was undertaken in this thesis to examine the resulting joint kinematics during application of an external load as well as the in-situ forces in the soft tissue structures at the glenohumeral joint. Three loading conditions were examined:​ an anterior-posterior load, a superior-inferior load, and an internal-external moment. A robotic/universal force-moment sensor testing system was used to apply the loads to ten intact shoulder specimens at four abduction angles while recording the resulting joint kinematics. The robot was then used to reproduce the kinematics of the intact shoulder for each loading case, and soft tissue structures were sequentially removed to determine the apparent in-situ force in each structure. Finally, the length of each glenohumeral ligament was determined by a three-dimensional kinematic model of a glenohumeral joint. The corresponding force in each structure was subsequently calculated based on the length via load-elongation curves obtained experimentally.

The results revealed that the stiffness properties of this joint reflect the need for stabilization at the extremes of motion, 0° and 90° of abduction. The passive properties of the rotator cuff musculature were also found to be important for resisting applied loads in this experimental model. Based on the apparent in-situ force at the joint due to separation of the capsule into its individual components, reasonably accurate measurements of the force in the glenohumeral ligaments may be made. However, the data also suggests that the continuous nature of the capsule be included in future experimental and computational studies. Finally, the validated mathematical model can now be used to predict the forces in the glenohumeral ligaments during more clinically relevant and complex joint motions.