2011 Volume 35 Issue 3 Pages 953-956
Internal impingement in the late cocking phase (LCP) is a physiological phenomenon but leads to pain and tissue trauma by excessive burden. We studied the change in the figure of internal impingement at LCP by pitching counts using open MRI. Ten high-school pitchers with no history of shoulder disorder were studied. ROM was measured before and after 100 pitches in a bull-pen. Oblique coronal slices of MRI were taken by open MRI with the shoulder in ABER position to simulate LCP, before and after the burden. The figure of the internal impingement was evaluated by a special MRI calculator (image J) by a radiologist. After pitching, the range of external rotation increased, and internal rotation decreased significantly from 143.0° to 146.7°, 51.0° to 45.6°, respectively. The restaged LCP position in the MRI was 131.4° degrees flexion, 117.0° external rotation, 14.6° horizontal abduction on average. All cases showed internal impingement before and after the exercise. The measurement from the greater tubercle, vertical length from the articular level of the rotator cuff to the deepest part of the impinged cuff increased significantly from 10.6 to 12.8mm and 5.0 to 6.27mm, respectively. The cuff had intervened in between the greater tubercle and the glenoid forming a triangular shape and the area had increased significantly from 34.3 to 42.7mm2. Considering the risk of pitching injury by number of pitches, the change of the figure of internal impingement at ABER simulating LCP showed by our study is an important phenomenon for the understanding of pitching injuries.
