Proximal to distal sequencing impacts on maximum shoulder joint angles and the risk of impingement in baseball pitching involving a scapular independent thoracohumeral model

Abstract

Background: Hyperangulation of the scapulohumeral joint due to poor coordination of the scapula during throwing motion is claimed to be a major cause of internal impingement in baseball pitchers. However, evidence of injurious scapular kinematics is lacking, particularly regarding how hyperangularion actually occurs in full-effort pitching. The purpose of this study was to describe sequential scapular motions involved in attaining maximum joint angles during pitching and the implications for internal impingement in elite baseball pitchers.Methods: An electromagnetic goniometer system computed kinematics for pelvis, thorax, scapulae, arms, and forearms during baseball pitching in 72 pitchers.Internal impingement risk was assessed based on kinematic characteristics of internal impingement quantified in a cadaveric study. Results:The pelvis, thorax, and scapula rotated in the proximal-to-distal sequence. Large forearm layback observed near the end of the cocking phase (182 ± 27°) was achieved with a submaximal scapulohumeral external rotation (98 ± 14°). In the next 0.027 ± 0.007 s, forward thoracic rotation and then scapular rotation caused increased scapulohumeral external rotation to a maximum of 113 ± 14°. Here, humeral horizontal adduction and scapula protraction occurred simultaneously preventing the humerus from lagging further behind the scapula.Only one participant reached critical hyperangulation beyond which internal impingement was reported to occur. Conclusion:Most elite pitchers safely attained the fully cocked position, yet off-timed recoiling of scapular protraction caused hyperangulation in full-effort pitching. Therefore, proximal-distal sequencing between the scapula and humerus should be evaluated to lessen the risk of internal impingement in baseball pitchers.

A novel method intersecting three-dimensional motion capture and medial elbow strength dynamometry to assess elbow injury risk in baseball pitchers

“…A Rapsodo system (Pitching 2.0, Rapsodo LLC) was used to measure the ball speed of each pitch. Pitching delivery motions were recorded with an electromagnetic tracking device 39 (Liberty, Polhemus, USA) which measured the six degrees of freedom of motion for two sensors attached to the participant’s body at the nominal sampling rate of 240 Hz. A system sensor was attached on the skin over the dorsal surface of the distal 1/5th of the forearm of the dominant side with double-sided tape and elastic tape and another sensor was attached to the upper arm with a plastic cuff that wrapped around the upper arm to minimize the influence of skin artifacts.…”