The kinetic chain of the throwing motion functions to optimize efficiency of proximal segments to decrease force loads seen at smaller, distal segments such as the ulnar collateral ligament. Several studies have shown that shoulder internal rotation forms the physiologic counter to the valgus torque generated during the late cocking phase of throwing. Previous studies have implicated decreased glenohumeral internal rotation as a cause of shoulder internal impingement. To date, an association between pathologic glenohumeral internal rotation deficit and elbow injury has not been exhibited.
Throwers with ulnar collateral ligament insufficiency will exhibit significantly increased glenohumeral internal rotation deficit.
Case control study; Level of evidence, 3.
Twenty-nine baseball players with ulnar collateral ligament insufficiency were demographically matched with 29 control baseball players who had no history of shoulder, elbow, or cervical spine injury. The investigators measured passive glenohumeral internal and external rotation, elbow flexion and extension, and forearm pronation and supination. The Mann-Whitney test was used to analyze continuous variables.
There were no significant differences between the groups in terms of demographics. There was a significant difference in dominant arm internal rotation, with injured players having significantly less (P < .004), and in glenohumeral internal rotation deficit between players with ulnar collateral ligament insufficiency and those who were asymptomatic (28.5° vs 12.7°; P < .001). Also, total range of motion was significantly decreased in the injured group. There were no significant differences in elbow or forearm range of motion between the groups.
Our results indicate that pathologic glenohumeral internal rotation deficit may be associated with elbow valgus instability. This has important clinical implications both in terms of preventing ulnar collateral ligament injury and with regard to rehabilitating throwers after ulnar collateral ligament reconstruction.