A methodology for estimating valgus stress during baseball pitching with one-segment model

Abstract

The purpose of this study was to test the validity of using a one- and a two-segment models for determining elbow joint valgus stress during baseball pitching. The one-segment model consisted of a single segment representing the ball, hand and forearm together as a rigid segment. The two-segment model consisted of a distal segment representing the ball, hand and forearm together as a rigid segment and a proximal segment representing the upper arm. In addition, a three-segment model, which is the most widely and frequently used model for determining the valgus stress of baseball pitching, was defined to provide a reference value for testing the validity of the fewer segment models. The three-segment model was comprised of a distal segment representing the ball and hand together as a rigid segment, a mid-segment representing the forearm and the proximal segment representing the upper arm. Fourteen university students with the baseball experience were asked to throw a baseball with their maximum effort and a motion capture analysis system (VICON, Oxford Metrics) was used to measure the motions of the segments. The result showed that the maximum values of the valgus stress determined with one- and two-segment models (approx. 64 Nm for fast balls) were significantly greater than the corresponding value determined with three-segment model (47 Nm), but the correlations among the three models were found to be significantly high (r > 0.83, p < 0.01). These findings suggest that the fewer segment models can be used to compare the magnitude of valgus stress among subjects and among pitches for evaluation of risk of elbow injuries.