In this thesis, the normal kinematics and pathomechanics of the shoulder have been studied. The optical technique of stereophotogrammetry was used to simultaneously obtain the normal articular and subchondral bone geometry, kinematics and contact patterns in the glenohumeral joint. It was determined that on average, the joint demonstrated minimal translations of the geometric center of the humeral head cartilage surface. Bone surface data, such as that obtained from radiographs, were shown to overestimate the incongruence and magnitude of translations in the joint. Elevation in external rotation was seen to be associated with larger translations of the humeral head center than when the arm was elevated with no external rotation.

It was observed that anterior tightening did not affect the position of the humeral head in the medial-lateral and inferior-superior directions, but did result in the center of the humeral head translating posteriorly throughout the range of motion. A computer simulation of anterior acromioplasty was performed to determine the appropriate location and amount of acromial bone removal necessary to eliminate impingement. Anterior third flattening eliminated impingement without sacrificing the integrity of the deltoid origin.

Sequential tears of the rotator cuff were created to determine their effect on experimentally obtained glenohumeral kinematics and contact. The supraspinatus tendon was observed to have both an active and a passive role in maintaining the position of the humeral head. The long head of the biceps was also noted to play an active role in stabilizing the humeral head especially in the presence of a large supraspinatus tear. Repair of the rotator cuff was seen to restore near normal kinematics characterized by small translations of the humeral head center through the range of motion.

A solution for the time-dependent creep response for two biphasic cartilage layers in a contact configuration was obtained. Fluid pressurization was seen to be the dominant load support mechanism immediately after load application. Differences in thicknesses of the layers were seen to cause a complex fluid flow pattern in which fluid flowed from the thinner layer into the thicker layer at small time. At intermediate time, the flow reversed in direction and flowed into the thinner layer from the thicker layer. At very large time, the fluid pressurization and fluid flow both dropped to zero. The principal effective stresses and the maximum shear stresses were also smaller in the thinner layers than in the thicker layers.