Josh B. Moosikasuwan, MDa, Theodore T. Miller, MDa*, David M. Dines, MDb aDepartment of Radiology, North Shore University Hospital, 825 Northern Boulevard, Great Neck, NY 11021, USA
bDepartment of Orthopaedic Surgery, Albert Einstein College of Medicine at Long Island Jewish Medical Center, 270-05 76th Avenue, New Hyde Park, NY 11040, USA
Throwing athletes are prone to shoulder injuries due to the extreme positioning of the shoulder in the various phases of the throw, the adaptive changes that develop over time to allow an advantageous arc of motion, and the chronic, repetitive nature of an activity that places such a high demand on the shoulder joint. The injuries are often particular to a specific phase of the throw and are well demonstrated with MRI. In this article, the authors review the phases of the throw, MRI techniques, and the MR appearances of the injuries associated with particular phases.
Baseball-throwing motion may be divided into six phases: wind-up, early cocking, late cocking, acceleration, deceleration, and follow-through. The position of the humerus during these phases changes in three dimensions: vertically in the coronal plane, horizontally in the anterior-posterior direction, and rota-tionally. Vertically, the humerus begins in minimal mild abduction during the wind-up phase and proceeds to 90° abduction in the early cocking phase, where it changes minimally and is maintained in 90° to 100° of abduction until it decreases at the end of the throw. In the horizontal plane, the humerus begins in a neutral position, is extended 15° posteriorly in the early cocking phase, starts to move forward in the late cocking phase, and is in approximately 35° and 60° of horizontal adduction in the deceleration and follow-through phases, respectively. Rotationally, the arm begins in internal rotation during the wind-up phase, is maximally externally rotated in the late cocking phase, and is then quickly internally rotated, ranging from 0° to 30° of internal rotation during
*Corresponding author. Department of Radiology, North Shore University Hospital, 825 Northern Boulevard, Great Neck, NY 11021. E-mail address: [email protected] (T.T. Miller).
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