Abstract
Total shoulder arthroplasty requires release of contracted tissues, repair of rotator cuff defects, reconstruction of normal skeletal anatomy with proper sizing, and positioning of components. Arthroplasty of the shoulder is unlike arthroplasty of the hinge joints when the collateral ligaments afford a high degree of stability and is even distinct from the hip when bony conformity is large and range of motion is less. Normal shoulder kinematics can only be achieved when normal articular anatomy is reestablished, and the passive and active stabilizers are balanced. This article presents the mechanics and pathomechanics of the glenohumeral joint for total shoulder arthroplasty.