Pectoralis Minor Contracture in Throwing Shoulders of Asymptomatic Adolescent Baseball Players.

BACKGROUND: Although scapular malpositioning is commonly associated with rotational deficits and risk of injury, modifiable causes of such malpositioning in overhead athletes are not well described.

PURPOSE/HYPOTHESIS: The purpose of this study was to examine the scapulothoracic profile of adolescent baseball players, specifically, pectoralis minor (PM) length. We hypothesized that PM would be shorter in throwing shoulders compared with nonthrowing shoulders.

STUDY DESIGN: Cross-sectional study; Level of evidence, 3.

METHODS: Forty-nine healthy adolescent baseball players underwent clinical screening of PM lengths in throwing and nonthrowing shoulders by means of previously described, validated techniques. PM measurements were conducted while players were supine with arms at rest, sitting with arms at rest, and sitting with shoulders in maximal external rotation; measurements were made with a digital caliper and by assessment of table-to-acromion distance. Static scapular position and range of motion measurements were recorded. Demographic information and playing history were documented.

RESULTS: All players were male, they had a mean ± SD age of 16.2 ± 1.16 years, and they predominantly threw right-handed (83.7%). Sixty-nine percent of players were pitchers, 61.2% had played baseball for 9 or more months per year, and 67.3% had played in excess of 30 games in the previous year. Significant differences were noted during side-to-side comparisons within participants. Absolute PM length was significantly shorter in throwing compared with nonthrowing shoulders when measured with players sitting with arms at rest (by 3.7 ± 11.8 mm) and with their shoulders in maximal external rotation (by 4.8 ± 15.1 mm) ( P < .004 for both). The PM index was significantly reduced in throwing compared with nonthrowing shoulders while players were supine with arms at rest ( P = .007), sitting with arms at rest ( P = .006), and sitting with shoulders in maximal external rotation ( P < .001). Mean table-to-acromion distance was increased 7.7 ± 1.26 mm in throwing versus nonthrowing arms ( P < .001). The scapular index was significantly reduced in throwing compared with nonthrowing shoulders ( P < .005).

CONCLUSION: Asymptomatic adolescent baseball players have significant differences in PM length and static scapular measurements in throwing compared with nonthrowing shoulders. The clinical significance requires further investigation, but emphasis on PM stretching routines is encouraged.