Relationship between range of motion of shoulder internal rotation and shoulder posterior laxity in semiprofessional baseball pitchers

Abstract

[Purpose] Internal rotation limitations (tightness) and posterior laxity of the shoulder, factors affecting throwers’ shoulder disorders, are seemingly contradictory phenomena. However, it is unclear whether they coexist in the pitchers’ shoulders. This study aimed to clarify the relationship between these two phenomena. [Participants and Methods] Forty-seven semi-professional pitchers were included in the study. Bilateral internal and external rotation range of motion and posterior laxity were measured. Subjects with ≥20° differences in the internal rotation range of motion between the right and left shoulders were included in the GIRD (glenohumeral internal rotation deficit) group (24 subjects) and those with differences <20° were included in the healthy group (23 subjects). Differences in the range of motion between the two groups and those in the positive rate of posterior laxity were tested. [Results] The internal rotation range of motion was significantly different between the GIRD (26.0 ± 12.6°) and healthy groups (50.0 ± 14.3°). There were no significant differences in the posterior laxity of the two groups. [Conclusion] Although the pitchers’ shoulders were shown to have limited internal rotation range of motion, the results suggest that posterior laxity can coexist with it.