Our hip stiffness score could be useful for the medical check-up of the pitchers.
During throwing, the force generated by the lower extremities is transferred through the core, shoulder, elbow, and ultimately, the hand before ball release via the kinetic chain. Proper positioning of the plant leg allows for optimal rotation of the hips, pelvis, and trunk, which could be crucial for providing the most effective transfer of energy through the kinetic chain. Therefore, an insufficient hip rotation range of motion (ROM) can arrest the throwing mechanics. Recently, we developed a new scoring system of hip stiffness (Hip Stiffness Score; HSS) for medical assessment of baseball players. In this study, we investigated the correlation between HSS and shoulder conditions in the baseball pitchers.
Materials And Methods
Twenty-seven professional baseball pitchers volunteered for this study. In shoulder evaluations, the ROMs of internal rotation (IR) and external rotation (ER) at 90 degree abduction were measured passively. HSS to quantitatively evaluate hip stiffness includes 4 physiologic parameters, including (1) straight leg raising (SLR) test (less than 80 degree in the non-throwing side or more than 5 degree deficit compared with the throwing side), (2) hip internal rotation and (3) adduction (HIR and HADD; more than 5 degree deficit in the non-throwing side compared with the throwing side), and (4) heel buttock distance (HBD; non-throwing side > throwing side). Bilateral glenohumeral internal and external-rotation ROM were measured passively. Then, they were summed for total arc of motion (TAM), and each difference between throwing and non-throwing side was calculated as glenohumeral internal rotation deficit (GIRD) and glenohumeral external rotation gain (GERG). IR and ER strength of shoulder were assessed bilaterally In the ultrasound assessments, all participants were scanned by using an AplioTM500 to assess the muscle thickness of supraspinatus (SSP) and infraspinatus (ISP).
HSS showed a mild positive correlation with TAM, weak positive correlations with GIRD and GERG, and weak negative correlations with IR and ER strength of shoulder. Then, the participants were divided into 2 groups according to HSS; more than 3 points of HSS was regarded as a high HSS group (n=12), and less than 2 points as a low HSS group (n=15). The GERG in the high HSS group was significantly greater than that in the low HSS (P<0.05), and the ER strength in the high HSS group was significantly lower than that in the low HSS (P<0.05). There were no significant differences in the GIRD, IR strength, and the thickness of SSP and ISP, but the thickness of ISP in the high HSS group was lower than that in the low HSS (P=0.08).
HSS has some correlations with TAM, GIRD, GERG, IR and ER strength of shoulder. It is assumed that the insufficient hip ROMs could inhibit the kinetic chain in throwing motion. Furthermore, the pitchers with the higher HSS showed greater GERG and lower ER strength. The increase of GERG and decrease of ER strength were reported to lead to shoulder and elbow injuries. Therefore, it is possible that the HSS could be useful for the medical check-up of the pitchers.