Effect of Younger Starting Pitching Age on Humeral Retrotorsion in Baseball Pitchers With an Ulnar Collateral Ligament Injury

Normalization Methods for Shoulder Strength in Baseball Athletes

BACKGROUND

Arm injuries in baseball continue to rise. Previous studies have confirmed relationships between shoulder strength, injury risk, and performance in baseball athletes. Shoulder strength measures vary considerably within and among baseball players and are influenced heavily by anthropometric measures. Presently, the normalization of shoulder strength measures has not been tested adequately to meet necessary statistical assumptions.

HYPOTHESIS

At least 1 shoulder strength normalization method would meet 2 statistical assumptions: the intercept assumption and correlation assumption.

STUDY DESIGN

Cross-sectional study.

LEVEL OF EVIDENCE

Level 3.

METHODS

Isometric shoulder strength was tested in a cohort of uninjured baseball athletes on the dominant limb via handheld dynamometry: external rotation (ER), internal rotation (IR), and scapular plane abduction (SCAP). Five normalization methods were assessed using 2 statistical assumptions to determine the most appropriate normalization method for each shoulder strength measure: first, the regression line between a participant characteristic (body mass, height, ulnar length, and their respective combinations) and the unnormalized strength measure passes through the origin; second, normalizing shoulder strength eliminates its correlation with the participant characteristics. Statistical significance was set a priori at α < 0.05.

RESULTS

Body mass normalization was the only normalization method that satisfied the intercept and correlation assumptions for ER, IR, and SCAP strength (P > .05).

CONCLUSION

Normalizing shoulder ER, IR, and SCAP strength in uninjured baseball athletes using body mass satisfied both statistical assumptions. When clinicians seek to compare shoulder strength in baseball athletes of differing anthropometric make-up, using body mass as the denominator is the most appropriate method for normalization.

CLINICAL RELEVANCE

The utilization of a statistically supported shoulder strength normalization method is warranted to account for anthropometric differences when comparing strength between athletes. This study adds a clinically relevant and reproducible method for normalizing isometric shoulder strength in uninjured baseball players.

The Role of Humeral Torsion on Glenohumeral Rotation in Injured Baseball Players

Background

Differences in rotational range of motion (ROM) compared to humeral retrotorsion (HRT)-corrected rotational ROM exist in healthy baseball athletes, but it is unclear whether these differences exist in a pathological population.

Purpose/Hypothesis

The purpose of this study was to determine if there are disparities between objectively measured differences in ROM and HRT-corrected deficits in injured baseball players. It was hypothesized that disparities would exist between (1) the side-to-side difference in glenohumeral external rotation (GER) and the HRT-corrected glenohumeral external rotation deficit (GERD) and (2) the side-to-side difference in glenohumeral internal rotation (GIR) and the HRT-corrected glenohumeral internal rotation deficit (GIRD).

Study Design

Cross-sectional study; Level of evidence, 3.

Methods

Data from 172 baseball players with shoulder or elbow injuries (45 shoulder, 127 elbow) were reviewed in July 2023. GER and GIR were measured on the injured and noninjured sides of all players, and diagnostic ultrasound was used to measure HRT. Dependent t tests were run to compare the side-to side differences in GER and GIR with the HRT-corrected GERD and GIRD, respectively.

Results

In the players with a shoulder injury, there was a significant disparity between the side-to-side difference in GER and the HRT-corrected GERD (2°± 14° vs -13°± 15°, respectively) and between the side-to-side difference in GIR and the HRT-corrected GIRD (-14°± 8° vs 2°± 9°, respectively) (P < .001 for both). Similarly, players with an elbow injury had significant disparities between the side-to-side difference in GER and the HRT-corrected GERD (6°± 9° vs -10°± 9°, respectively) and between the side-to-side difference in GIR and the HRT-corrected GIRD (-12°± 8° vs 4°± 10°, respectively) (P < .001 for both).

Conclusion

The results supported our hypothesis that there were disparities between objectively measured differences in GER and GIR compared with the HRT-corrected GERD and GIRD in injured baseball players. Consideration must be given to osseous adaptations that occur at the glenohumeral joint when evaluating and treating this population.