Intraclass correlation coefficients ranged from 0.47 to 0.87 for the right arm and 0.62 to 0.84 for the left arm, indicating moderate to good intrarater reliability22 of our procedure, with a standard error of measurement of 5.8° for the right arm and 5.3° for the left arm. Interrater reliability for measurements was 0.20 for the right arm and 0.40 for the left arm. Percent agreement was high (>85%), and percent chance agreement (81%). Mullaney et al23 report that using a digital leveler to measure the ROM of the shoulder is reliable, with a rotation measurement error of ±3° and an ability to detect differences in ROM of 6° with the same examiner and 15° between different examiners.
In this study of asymptomatic minor league baseball players, we found that over half had measurable loss of shoulder motion compared with their contralateral shoulder. Many previous studies have offered treatment algorithms to improve shoulder ROM. Sleeper stretch and cross stretching most commonly have been shown to improve IR. Many experienced therapists and athletic trainers have developed their own treatment regimen of stretching. With this study, we attempted to validate scientifically what we had observed anecdotally about the relationship between SI joint tightness and posterior shoulder capsule tightness. Our results demonstrated that internal end-range rotation improved with the “benchmark” sleeper's stretch; however, rotation improved twice as much stretching the contralateral SI joint.
Although tightness of the pelvis causing tightness of the shoulder is a new concept and much more research needs to be done to understand the reason behind this phenomenon, several studies show the correlation between loss of motion in the hip with loss of motion in the shoulder in pitchers from youth to professional baseball.2-32
Commonly, baseball players have been noted to possess decreased trunk rotation, shoulder IR of the throwing arm, external rotation of the dominant hip, and IR of the nondominant hip.27,33 Zeppieri et al32 demonstrated that the nondominant (lead) hip ROM and strength decreased over the course of a season. Picha et al31 found differences in ROM of both the hip and shoulder in youth baseball pitchers.
At present, a paucity of literature exists to support the complex relationship between the lower back and GIRD. However, two studies investigated improvement in shoulder range of motion with rotating the trunk along with stretching the shoulder.7,34
The pitching motion is a kinetic chain. In the past, most of the literature focused on the upper extremity in pitchers. MacWilliams et al35 pioneered the importance of the lower extremity in contributing in the throwing motion and suggested that strengthening of the lower extremities could enhance performance and avoid injury. The force generated by the large muscles of the lower extremity and trunk during the wind-up and stride phases are transferred to the ball through the shoulder and elbow during the cocking and acceleration phases.36 Breaks in this kinetic chain are known to increase the risk of injury.
Perhaps the great forces generated in the wind-up and stance phases throw the pelvis out of alignment, producing GIRD. If this phenomenon proves to be true, orthopaedic surgeons must not simply focus on the shoulder of overhead athletes with GIRD, getting mixed results, but also evaluate the lower back, looking for the true source of an injury, thus, obtaining quick, long-lasting relief and preventing future injuries. As the saying goes, “The trunk must be stable to support the limbs.”
There are several limitations to this study. First, the sample size is small, and the sizes between randomized groups are uneven. In addition, the cohort included both pitchers and position players. Future studies should attempt to study a more homogenous group. We also had measurements only for one point in time; thus, it is impossible to conclude whether the range-of-motion gains were maintained over time. We do not have any data on our study subjects regarding injuries, pain, or games missed due to pain/injury. We used a novel approach to our range of motion measurements that has not been validated in the literature. On the basis of this small pilot study, we recommend future research to confirm our findings. Because our study focused on only minor league baseball players, our findings may not be generalizable to other athletes or patient populations.
On the basis of our data, there may be a subset of baseball players with a glenohumeral internal rotation deficit that is in part caused by SI joint tightness and may benefit or resolve from stretching the pelvis. Further anatomic and functional research studies are necessary to understand this pathophysiology.
The authors thank the entire Schaumburg Boomer Baseball Team, Jamie Bennet (manager), and Pat Salvi (owner) for graciously allowing them to conduct this research. They are also thankful to Ms. Nadia Poponne and Ms. Cynthia Wenham, Librarians, Ross University School of Medicine, and Ms. Lisa Blackwell, Director Library Services, Chamberlain University for their help in locating references used in this investigation. In addition, they thank the Resource Sharing and Print Resources Access Management units, Drexel University Libraries, for their help in locating references used in this investigation.
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