Biomechanics of the Shoulder: Stability and Kinematics of Shoulder Motion, Throwing Kinematics

The shoulder has the greatest range of motion of any joint in the body. This unique characteristic is necessary for enabling the hand to be placed in the multitude of positions required for activities of daily living as well as sporting activities. The stability and function for the glenohumeral joint are provided by a complex and intricate coordinated interplay of the active and passive stabilizers, which in turn places great mechanical demands on the shoulder. In throwers, the mechanical demands are even greater, where a tremendous amount of forces act on the shoulder, as the throwing motion requires a rapid transmission of force from the lower extremity and core to the upper extremity. Therefore, in a thrower’s shoulder, maintaining stability and achieving precise kinematics throughout all phases of throwing require a complex interplay between the scapula, humerus, and all scapulohumeral and scapulothoracic muscles. These forces and velocities place the shoulder at great risk of injury, especially in the setting of improper mechanics.