The Area of Impingement in the Throwing Versus Nonthrowing Shoulder of Collegiate Baseball Players: An MRI Study of the Simulated Late-Cocking Phase of Throwing

Abstract

Background: During shoulder abduction and external rotation, internal impingement can occur when compressive forces between the greater tuberosity and the posterior glenoid rim pinch the undersurface of the rotator cuff. Previous studies on internal impingement have focused on qualitative results such as pathological findings; however, few studies have quantified the area of impingement (AOI) of the rotator cuff muscles between the greater tuberosity and the posterior glenoid rim. Purpose: To compare the AOI between the throwing and nonthrowing shoulders of baseball players. Study Design: Controlled laboratory study. Methods: A total of 14 asymptomatic male collegiate baseball players participated in this study. The AOI in both the throwing and the nonthrowing shoulders was calculated using magnetic resonance imaging (MRI) scans. The MRI measurements were collected with the shoulder at 90° of abduction and at 90° and 100° of external rotation. The area, width, and depth of impingement as well as cystic changes in the greater tuberosity and degeneration in the posterior labrum were compared between the throwing and nonthrowing shoulders. Results: The AOI was significantly greater in the throwing shoulders than in the nonthrowing shoulders (90° of external rotation: 32.4 vs 19.1 mm2, respectively; 100° of external rotation, 28.0 vs 15.6 mm2, respectively; P < .001 for both). Compared with the nonthrowing shoulders, there were more positive findings in the throwing shoulders regarding greater tuberosity cystic changes (0 vs 7, respectively; P = .006) and posterior labral degeneration (3 vs 13, respectively; P < .001). Conclusion: The AOI and the number of lesions in the greater tuberosity and posterior labrum were greater in throwing shoulders than in nonthrowing shoulders. Therefore, damage to the insertion of the rotator cuff muscles may affect internal impingement. Clinical Relevance: Lesions in the greater tuberosity and posterior labrum in throwing shoulders may increase the AOI by expanding the joint gap behind the glenohumeral joint. Impingement of the greater tuberosity and the posterior glenoid rim may lead to rotator cuff tears.

RETRACTED: Effect of Morphologic Changes in the Posterior Glenoid Rim on Rotator Cuff Impingement in Baseball Players

“…From the results of this study, the PGHD was associated with AOI, which re ected the rotator cuff tendons existing between the greater tuberosity and posterior glenoid rim. Takahashi et al [15] reported that the AOI of the throwing shoulder with morphologic change in the posterior glenoid rim was higher than that of the non-throwing shoulder, indicating an increase in the area of the rotator cuff tendons between the humeral head and posterior glenoid rim. Morphologic changes in the posterior glenoid rim diminish the bumper effect of the posterior glenoid rim and impair its protective role as a "wall."…”

“…Previous studies have focused on internal impingement, which is a phenomenon wherein the undersurface of the rotator cuff tendons is pinched between the greater tuberosity and posterior glenoid rim during shoulder abduction and external rotation of the late cocking phase [6]. Internal impingement syndrome is frequently observed in baseball players and is associated with throwing shoulder injuries, such as rotator cuff injury, labrum injury, and humeral head cysts [7][8][9][10][11][12][13][14][15].…”

“…Since complex shoulder joint morphologic changes may lead to throwing shoulder pain and disabled throwing shoulder [7-9, 16, 17], it is crucial to understand the in uence of morphological changes on the throwing shoulder. Using the area of impingement (AOI) of the rotator cuff [15], it has been reported that compared with the non-throwing shoulder, the throwing shoulder has a larger area of rotator cuff tendons pinched within the glenohumeral joint. Takahashi et al reported that the higher the AOI on the throwing shoulder was, the higher the morphologic changes in the posterior glenoid rim [15].…”

“…Using the area of impingement (AOI) of the rotator cuff [15], it has been reported that compared with the non-throwing shoulder, the throwing shoulder has a larger area of rotator cuff tendons pinched within the glenohumeral joint. Takahashi et al reported that the higher the AOI on the throwing shoulder was, the higher the morphologic changes in the posterior glenoid rim [15]. However, the morphologic changes in the posterior glenoid rim have only been qualitatively assessed and not quantitatively measured.…”

Understanding the Disabled Throwing Shoulder Requires Updated Review of Anatomy, Mechanics, Pathomechanics, and Treatment

“…Shoulder health and pathology in the overhead athlete remains a particularly important topic of scholarship today. [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] Thus, in this issue, we feel very fortunate to publish the very latest:…”