The Association between Excessive Glenohumeral External Rotation and Risk for Shoulder and Elbow Injury in Left-Handed High School Baseball Pitchers: A Prospective Cohort Study

Abstract

Background:

Left-handed baseball pitchers exhibit unique throwing biomechanics, yet the risk factors for shoulder and elbow injuries in this population remain unclear.

Purpose:

To prospectively investigate preseason risk factors for shoulder and elbow injuries in left-handed high school baseball pitchers.

Study Design:

Cohort study; Level of evidence, 2.

Methods:

A total of 160 left-handed high school baseball pitchers were enrolled. Preseason evaluations included age, height, weight, shoulder muscle strength, and range of motion of the shoulder and elbow. Participants completed a self-recorded questionnaire on shoulder and elbow pain and associated pitching limitations during the subsequent season. Participants were categorized into the noninjured or injured group. The Mann-Whitney U test, chi-square test, logistic regression analysis, and receiver operating characteristic curve analysis were used to identify injury risk factors and cutoff values for shoulder and elbow injuries.

Results:

Shoulder and elbow injuries occurred in 27 participants (16.9%). The injured group had significantly greater abduction–external rotation (ABER) in the dominant shoulder (114.8°± 11.9° vs 107.5°± 13.0°; P = .008) and a greater total arc of the dominant shoulder (166.4°± 25.1° vs 156.0°± 23.4°; P = .039). Logistic regression analysis showed that ABER in the dominant shoulder was an independent risk factor for injuries (P = .031; OR, 1.04). Receiver operating characteristic curve analysis determined that an ABER ≥109° predicted injury (P = .017). Pitchers with ABER ≥109° had a 3.3 times higher incidence of injury than those with ABER <109° (P = .005).

Conclusion:

Increased shoulder ABER was significantly associated with shoulder and elbow injuries among left-handed high school baseball pitchers. Pitchers with ABER ≥109° are at higher risk.

Keywords

shoulder and elbow injuries left-handed pitchers shoulder abduction–external rotation (ABER)baseball pitching mechanics range of motion

The overhead throwing motion required in baseball pitching places immense demands on the shoulder and elbow joints, making pitchers particularly susceptible to injury.^21,22,28

Prospective cohort studies have been performed among baseball players from the youth to the professional level, and many risk factors for shoulder and elbow injuries have been reported. At the professional level, elbow varus at maximum external rotation (fastest strike), pitching motion,¹ high pitch velocity,² preseason supraspinatus weakness, prone external rotation (PER) strength deficits,³ glenohumeral internal rotation deficit (GIRD),^26,27 shoulder external rotation insufficiency,^26,27 total rotation deficit,^26,27 and shoulder flexion deficit^26,27 have been reported as risk factors. In high school baseball players, scapular dysfunction,¹⁰ GIRD,^13,14 preseason PER weakness,¹⁴ and preseason supraspinatus weakness²⁴ are associated with an increased risk of injury. At the youth level, playing pitcher,^4,9 pitching >100 innings in 1 year,⁴ throwing a curveball before the age of 13 years,⁴ playing catcher,^4,9 older age,⁸ and a history of elbow pain⁸ have been reported as risk factors. The aforementioned risk factors were investigated without distinguishing between left- and right-handed pitchers.

Studies have increasingly reported that left- and right-handed baseball players have different physical characteristics and anatomies. Previous research has demonstrated that professional right-handed pitchers exhibit significantly greater glenohumeral external rotation in their throwing arms than their left-handed counterparts.⁶ Additionally, right-handed pitchers display larger glenohumeral internal rotation deficits and more substantial side-to-side differences in humeral retrotorsion than left-handed pitchers.⁶ Conversely, left-handed pitchers demonstrate notably greater flexion deficits in their throwing arms than right-handed pitchers.⁶ At a young age, left-handed pitchers exhibit notably smaller side-to-side differences in their glenohumeral external rotation angle and humeral torsion angle than their right-handed counterparts.²⁵ These anatomic and functional differences between right- and left-handed players may influence injury risk profiles. Because left-handed pitchers are the minority, accounting for approximately 25% in the previous study,⁶ we thought that a study with a large sample size might not have a significant effect on the risk factors for right-handers; however, because left-handers are the minority, their risk factors are likely to be different.

To our knowledge, no previous study has examined the specific risk factors for shoulder and elbow injuries in left-handed high school baseball pitchers. Therefore, this study aimed to investigate preseason risk factors for shoulder and elbow injuries in left-handed high school baseball pitchers, hypothesizing that these risk factors would differ from those previously reported in studies focusing on right-handed pitchers.

Methods

Participants

We recruited participants at the annual preseason medical checkups, which are conducted for high school baseball pitchers at Gunma University Hospital in February each year. Between 2013 and 2018, 788 high school baseball pitchers aged 15 to 17 years participated in the annual preseason medical checkups.

Included were players who (1) consented to participate in this prospective study, (2) participated in preseason practice as an active player, (3) had no restrictions on their pitching activities, and (4) completed a daily questionnaire on the presence of shoulder/elbow pain, which was collected every month throughout the season.¹⁴ Those who had (1) previous injury to the throwing arm and (2) an inability to play baseball owing to shoulder or elbow injuries were excluded.¹⁴

The Institutional Review Board of Gunma University Hospital (identification No. 1003) approved this study, and all methods were conducted in compliance with the relevant guidelines and regulations.

Preseason Medical Checkups

As described in previous studies, preseason medical evaluations were conducted to assess the condition of the participants’ shoulders and elbows and identify potential risk factors for injury. To minimize bias, the examiners were blinded to the handedness of the participants. The assessments included measurements of body weight, height, shoulder and elbow range of motion (ROM), and shoulder muscle strength.^14,17,19

Shoulder and Elbow ROM

The intrarater validity and reliability of ROM measurements performed using a digital protractor have been established in a previous study.¹⁴ As previously reported,^14,17,19 a certified orthopaedic surgeon used a digital protractor (iGaging) to measure the passive ROM in elbow flexion and extension, as well as passive horizontal adduction (HA), abduction–external rotation (ABER), and abduction–internal rotation (ABIR) of the dominant and nondominant shoulders. All measurements were performed with participants in the supine position. For passive HA, the examiner (R.M.) stabilized the axillary border of the scapula, while another certified orthopaedic surgeon (F.I.) placed a digital protractor on the humerus. For passive ABER and ABIR, the examiner (R.M.) applied a posterior force to the coracoid process to stabilize the scapula, and another certified orthopaedic surgeon (F.I.) placed the digital protractor on the forearm. The total arc for each shoulder was calculated by adding the 90° of ABER and ABIR measurements. The difference in the ROM measurements was calculated as the difference between the values of the dominant and nondominant sides.

Shoulder Strength

The intrarater validity and reliability of shoulder strength measurements performed using handheld dynamometers have been previously established.¹⁴ As in previous studies,^14,17,19 a certified orthopaedic surgeon (R.M.) assessed the strength of the supraspinatus in the seated position (SS), PER, and prone internal rotation (PIR) in both shoulders using a PowerTrack II Commander handheld dynamometer (JTech Medical).

The SS strength was assessed with the participant seated on an examination table with their back against a wall. The participants abducted the humerus to 90° in the coronal plane and then horizontally adducted it to 45° with the forearm in a neutral position. A handheld dynamometer was placed 5 cm proximal to the proximal wrist extension crease, and the participant was instructed to raise their forearm. To measure PER strength, the dynamometer was positioned on the dorsal aspect of the forearm, 5 cm proximal to the wrist extension crease.

Each strength measurement was performed 3 times, and the median value was used in the analysis. The SS, PER, and PIR strength ratios of the dominant and nondominant arms were calculated for each participant. Additionally, the ratio of dominant arm PER to dominant arm PIR strength was determined.

Injury Tracking

A shoulder or elbow injury was defined as any condition resulting in the pitcher being considered disabled for ≥8 days, excluding injuries owing to external forces, such as being hit by a ball, colliding with another player, or falling.^14,17,19 Participants completed daily questionnaires reporting the presence of shoulder or elbow pain, any associated limitations to their pitching activities, and the occurrence of any other injuries. This allowed researchers to track the timing of any reported injuries and mitigate the risk of recall bias. The participants’ responses were submitted to the researchers every month. Injury tracking was performed for 1 season and was initiated immediately after the preseason medical checkup.

Statistical Analysis

The incidence rates of shoulder and elbow injuries were calculated for initial injuries to the upper extremities during the season. The pitchers were then categorized into the injured or noninjured group based on reported injuries. Continuous data were reported as means with standard deviations, and group differences were assessed using the Mann-Whitney U test. Logistic regression analysis was performed, adjusting for significant variables identified in the univariate analyses, to determine the risk factors for shoulder and elbow injuries and to calculate the corresponding odds ratios and 95% confidence intervals. Receiver operating characteristic (ROC) curve analysis and the Youden index were used to identify the cutoff point of the detected risk factors to determine the incidence of shoulder and elbow injuries. Finally, to confirm the appropriateness of the detected cutoff value, we adjusted the cutoff values and performed a sensitivity analysis as follows: (1) calculated the corresponding sensitivity and specificity, (2) compared the incidence of injury between the groups categorized by the shifted cutoff, and (3) performed logistic regression analysis using the shifted cutoff values.

All statistical analyses were conducted using IBM SPSS Statistics Version 29 software (IBM Japan, Ltd), with a significance set at a P value <.05.

Statistical power analysis was conducted before the study to determine the required sample size. For the planned logistic regression analysis, we calculated that 70 participants would be needed to determine statistical significance, assuming 80% statistical power, an incidence rate of 20%, and an odds ratio of 2.5 based on previous research.²⁸ All statistical analyses comply with the CHAMP (Checklist for Statistical Assessment of Medical Papers) statement.⁸

Equity, Diversity, and Inclusion Statement

The author group consists of junior, midcareer, and senior researchers, including both female and male authors. However, all members of the author group are from 1 country. Our study population included high school pitchers from public and private schools participating in competitive baseball teams.

Results

Overall, 788 high school baseball pitchers participated in preseason medical checkups between 2013 and 2018. Among them, 127 (including 27 left-handed pitchers) were excluded because they refused to participate in the study. Informed consent was obtained from 661 pitchers (501 right-handed and 160 left-handed). Because we had no dropouts, the 160 left-handed pitchers (24.2%) served as the study population. Shoulder and elbow injuries were observed in 27 participants (16.9%) (Figure 1).

Figure 1.

Flow diagram showing participant recruitment, eligibility, enrollment, follow-up, and analysis.

Baseline Characteristics

In the injured group, ABER in the dominant shoulder was significantly greater than that in the noninjured group (114.8°± 11.9° vs 107.5°± 13.0°; P = .008). The total arc of the dominant shoulder in the injured group was also significantly greater than that in the noninjured group (166.4°± 25.1° vs 156.0°± 23.4°; P = .039). No significant differences were observed in the other measured parameters, including age, height, weight, elbow ROM, and shoulder strength, between the injured and noninjured groups (Table 1).

Table 1

Baseline Characteristics of the Study Participants ^a

	Noninjured (n = 133)		Injured (n = 27)		P Value
	Mean	SD	Mean	SD	P Value
Age, y	16.4	0.6	16.6	0.7	.520
Height, cm	171.6	5.5	172.1	5.2	.693
Weight, kg	66.5	7.7	66.5	7.7	.986
Elbow ROM, deg
Flexion in dominant side	144.1	4.2	143.1	7.1	.543
Flexion in nondominant side	147.1	5.4	145.5	5.2	.187
Extension in dominant side	2.5	5.9	0.3	9.6	.302
Extension in nondominant side	5.8	5.0	4.6	6.5	.346
Difference in flexion	–3.0	5.2	–2.3	5.9	.575
Difference in extension	–3.2	5.1	–4.3	5.8	.388
Shoulder ROM, deg
ABER in dominant side	107.5	13.0	114.8	11.9	.008
ABER in nondominant side	93.1	26.3	100.9	23.3	.156
ABIR in dominant side	48.5	22.8	51.6	23.8	.514
ABIR in nondominant side	49.2	13.3	52.1	15.1	.303
Total arc in dominant side	156.0	23.4	166.4	25.1	.039
Total arc in nondominant side	142.3	30.4	153.0	30.2	.096
HA in dominant side	19.1	14.6	23.1	19.8	.333
HA in nondominant side	26.2	15.0	29.2	18.3	.364
Difference in ABER	14.4	21.8	13.9	19.8	.910
Difference in ABIR	–0.7	23.8	–0.5	27.7	.969
Difference in total arc	13.7	42.7	13.4	43.9	.973
Difference in HA	–7.0	9.6	–6.1	9.3	.641
Shoulder strength
PER in dominant side, kg	19.8	8.0	20.6	7.1	.608
PER in nondominant side, kg	21.4	8.8	23.2	8.1	.338
PIR in dominant side, kg	24.5	10.0	24.9	9.8	.837
PIR in nondominant side, kg	22.6	8.9	22.8	7.2	.893
SS in dominant side, kg	17.7	11.6	17.8	9.6	.960
SS in nondominant side, kg	17.8	11.3	19.2	11.5	.647
PER ratio	0.9	0.2	0.9	0.1	.270
PIR ratio	1.1	0.2	1.1	0.2	.904
SS ratio	1.0	0.2	1.0	0.1	.306
PER/PIR ratio in dominant side	0.8	0.2	0.9	0.2	.450
PER/PIR ratio in nondominant side	1.0	0.2	1.0	0.2	.093

Difference = range of motion (ROM) in the dominant side – ROM in the nondominant side; ratio = strength in the dominant side/strength in the nondominant side. Bold P values indicate statistical significance (P < .05). ABER, ROM of 90° of abduction–external rotation in the shoulder; ABIR, ROM of 90° of abduction–internal rotation in the shoulder; HA, ROM of horizontal adduction in the shoulder; PER, strength of prone external rotation; PIR, strength of prone internal rotation; SS, strength of the supraspinatus in the seated position.

Logistic Regression Analysis

Based on the results of the univariate analysis, ABER and total arc in the dominant shoulder were used as explanatory variables in the multivariate logistic regression analysis. Logistic regression analysis showed that ABER in the dominant shoulder was a significant independent risk factor for shoulder and elbow injury (P = .031; OR, 1.042; 95% CI, 1.004-1.082) (Table 2).

Table 2

Results of the Logistic Regression Analysis ^a

	OR	95% CI	P Value	VIF
ABER in the dominant shoulder	1.042	1.004-1.082	.031	1.143
Total arc in the dominant shoulder	1.012	0.993-1.031	.206	1.143

Bold P value indicates statistical significance (P < .05). ABER, range of motion of 90° of abduction–external rotation in the shoulder; VIF, variance inflation factor.

ROC Curve Analysis

ROC curve analysis revealed that the cutoff value of ABER in the dominant shoulder for predicting shoulder and elbow injuries was 109° (P = .017; area under the curve, 0.65; Youden index, 0.297).

Pitchers with ABER ≥109° in the dominant shoulder had a 3.3 times higher incidence of shoulder and elbow injuries than those with ABER <109° (P = .005) (Table 3).

Table 3

Results of the Sensitivity Analyses ^a

Cutoff Value, deg	Sensitivity	Specificity	Chi-Square Test	Logistic Regression Analysis
Cutoff Value, deg	Sensitivity	Specificity	P Value	OR	95% CI	P Value
107	0.74	0.47	.048	2.314	0.908-5.901	.079
108	0.74	0.49	.029	2.614	1.025-6.670	.044
109	0.74	0.56	.005	3.256	1.278-8.298	.013
110	0.70	0.59	.005	3.096	1.250-7.671	.015
111	0.63	0.62	.018	2.438	1.024-5.807	.044

Bold P values indicate statistical significance (P < .05).

Sensitivity Analysis for Validation of Cutoff Value

To confirm the appropriateness of the 109° cutoff value for ABER in the dominant shoulder, we adjusted the cutoff values by ± 2 (107°, 108°, 109°, 110°, and 111°) and performed a sensitivity analysis as follows: (1) calculated the corresponding sensitivity and specificity, (2) compared the injury incidence between the groups categorized by the adjusted cutoff, and (3) performed logistic regression analysis with the adjusted cutoff values (Table 3).

When using 107°, 108°, 109°, 110°, and 111° as the cutoff values, the sensitivities were 0.74, 0.74, 0.74, 0.70, and 63.0, respectively, and the specificities were 0.47, 0.49, 0.56, 0.59, and 0.62, respectively. The 109° cutoff value demonstrated a relatively good balance between sensitivity and specificity.

The chi-square test showed a significantly higher incidence of injury in pitchers with all adjusted cutoff values (P < .05).

Logistic regression analysis using the adjusted cutoff values showed that the 109° cutoff was the most robust predictor of shoulder and elbow injury, with the highest odds ratio (P = .013, OR, 3.3, 95% CI, 1.3-8.3).

The findings indicated that a 109° threshold for ABER in the dominant shoulder was an appropriate predictor of shoulder and elbow injury risk among left-handed high school baseball pitchers.

Discussion

The primary finding of this study was that a greater shoulder ABER in the dominant shoulder was an independent risk factor for shoulder and elbow injury in left-handed high school baseball pitchers. Specifically, pitchers with ABER ≥109° in the dominant shoulder had a 3.3 times higher incidence of shoulder and elbow injury than those with ABER <109°. However, it should be noted that the ROC value of 0.65 and a Youden index of 0.30 indicate only a fair predictive ability for this cutoff. To our knowledge, this is the first study to identify the specific risk factors for shoulder and elbow injuries among left-handed high school baseball pitchers.

Differences Between Right- and Left-Handed Baseball Players

The differences between right- and left-handed baseball players, particularly pitchers, span various physical, biomechanical, and performance aspects.

In professional baseball pitchers, left-handed pitchers demonstrated a significantly smaller ROM in ABER (112.7° vs 118.5°) in their throwing arms than their right-handed counterparts.⁶ Furthermore, left-handed pitchers exhibited significantly greater flexion deficits in their throwing arms than right-handed pitchers.⁶ In collegiate pitchers, no statistically significant differences were observed in the ABER and total arc in the pitching arm between the right- and left-handed pitcher groups. However, the ABIR in left-handed pitchers was significantly greater than that in their right-handed counterparts.²⁰ In young baseball pitchers (aged 9-12 years),²³ the right-handed group exhibited significantly greater ABER in their throwing arms than in their nonthrowing arms. However, the left-handed group showed no significant side-to-side differences in ABER. Furthermore, the left-handed group displayed a significantly smaller ABER difference between the throwing and nonthrowing arms than the right-handed group. However, no significant difference was observed in the adjusted ABER between the throwing and nonthrowing arms in the 2 groups.

In the present study, the observed 14° side-to-side difference in ABER between injured and noninjured pitchers may be attributed to several factors. One possible explanation is cumulative adaptations from repetitive throwing, where repeated overhead motions gradually increase shoulder external rotation over time. Additionally, differences in throwing mechanics between left-handed and right-handed pitchers might contribute to this disparity, as left-handed pitchers often exhibit unique kinematic patterns during the pitching motion. Furthermore, inherent physical characteristics specific to left-handed pitchers, such as variations in humeral torsion or joint laxity, could also play a role in this difference.

These side-to-side differences in shoulder ROM between the throwing and nonthrowing shoulders are likely because of the unique stresses placed on the dominant arm during throwing. These findings, along with previous literature, suggest that left-handed pitchers may have a risk profile distinct from that of right-handed pitchers.

Throwing-Related Arm Injury in Left-Handed Pitchers

Yokoya et al²⁹ investigated the side-to-side differences in shoulder conditions in 25 baseball pitchers (mean age, 20.8 years) with shoulder injuries and reported that the ABER and total arc showed no significant differences between sides (throwing side vs nonthrowing side; ABER: 102.5 ± 11.8° vs 99.4 ± 7.6°, total arc: 151.5 ± 13.8° vs 154.9 ± 11.8°). The ABIR in the throwing side had significantly lower angles than that in the nonthrowing side (throwing side vs nonthrowing side; 49.0 ± 9.6° vs 55.5 ± 10.4°; P = .01). The HA in the throwing side was significantly larger than that in the nonthrowing side (throwing side vs nonthrowing side; 125.0 ± 10.5° vs 113.9 ± 9.3°; P = .002). The previous study²⁹ indicates that ABIR and HA characteristics may differ between the throwing and nonthrowing sides in left-handed pitchers with shoulder injuries. However, the specific risk factors for shoulder and elbow injuries among left-handed baseball pitchers remained unclear because the study had a cross-sectional design without a comparison with uninjured left-handed pitchers. Our current prospective study focused solely on left-handed pitchers and found that an increased ABER in the dominant shoulder was a risk factor for shoulder and elbow injuries in left-handed high school baseball pitchers.

Relevance of Shoulder ABER as a Risk Factor

An excess of ABER ROM, which can increase anteroinferior instability,²⁵ may be modified using proprioception and motor control exercises.¹² Excessive ABER can mechanistically increase the risk of injury to soft tissue structures through internal impingement.⁷ As the humerus rotates externally, the biceps tendon and rotator cuff twist and stretch. Additionally, the rotator cuff and labrum may become impinged between the greater tuberosity and the posterior-superior glenoid margin at the end of the ROM.⁷ Similarly, increased ABER is associated with a heightened risk of injury to the elbow, particularly involving the ulnar collateral ligament.^11,25,27 Previous studies have suggested that an excess of ABER could potentially increase the risk of shoulder and elbow injuries. In this study, left-handed high school baseball pitchers with ABER ≥109° in their dominant shoulders were at a 3.3-fold significantly greater risk of developing shoulder or elbow injuries during the season than pitchers with ABER <109°.

These findings align with those reported in previous studies.^11,25,27 However, future follow-up studies are required to determine the validity of the ABER cutoff values.

Relationship Between Increased External Rotation and Pitch Velocity

Increased ABER of the shoulder has been shown to enhance pitch velocity,⁵ as it allows for greater energy storage and transfer during the late cocking and acceleration phases of pitching. However, the mechanical advantage conferred by increased external rotation comes at a cost: heightened stress on the shoulder and elbow structures. A greater external rotation can amplify anterior capsular laxity, increase internal impingement, and lead to greater valgus stress on the elbow, potentially predisposing pitchers to ulnar collateral ligament injuries.²⁶

Previous studies have reported that higher pitch velocity is a known risk factor for throwing-related injuries in professional² and youth baseball players.⁴ While our study did not directly measure pitch velocity, the increased shoulder ABER observed in injured players may indirectly reflect the biomechanical adaptations associated with achieving higher pitch velocities. Future studies should investigate the interplay between shoulder external rotation, pitch velocity, and injury risk to better understand these relationships and develop targeted preventive strategies.

Clinical Relevance

Our findings provide important clinical insights for athletes, coaches, and medical professionals working with high school left-handed baseball pitchers. Pitchers with ABER ≥109° should be identified during preseason assessments as being associated with a higher risk of shoulder and elbow injuries. To address this risk, training and rehabilitation programs should focus on managing shoulder external rotation, improving rotator cuff strength, and ensuring scapular stability to reduce excessive joint stress. Additionally, maintaining a balanced PER/PIR strength ratio is essential to minimize asymmetric loading on the shoulder. Coaches should also monitor throwing volume and intensity, particularly in pitchers with excessive ABER, to prevent cumulative stress on the shoulder and elbow. By integrating these approaches into regular training and rehabilitation protocols, it may be possible to reduce injury risk and support the long-term health and performance of left-handed pitchers.

Limitations

This study has some limitations. First, we did not evaluate humeral torsion, which plays a critical role in determining the contribution of bony torsion versus soft tissue adaptation to shoulder external rotation. Without this information, it is unclear whether the increased external rotation observed in this study is primarily due to humeral retroversion or soft tissue stretching. Future studies should include retroversion measurements to better understand the biomechanical factors contributing to shoulder and elbow injury risk. Second, we did not assess lower extremity biomechanics, which can influence throwing mechanics and injury patterns. Third, we did not evaluate pitching volume and overall baseball loads (practice, training, competition hours), which could potentially affect the occurrence of throwing injuries. However, in high school baseball pitchers, controversy exists regarding how pitching and overall baseball loads affect the risk of injury. While some studies have identified a small number of daily pitches (<30 pitches/day)¹⁸ and high overall baseball loads (<5.5 h/day)¹⁶ as risk factors for shoulder and elbow injuries among high school baseball pitchers, no sufficient evidence yet exists to definitively determine the effect of pitching and overall baseball loads on the risk of injury. Fourth, our sample size, while adequate for the analyses, may not have captured all potential risk factors. Fifth, this study did not measure pitch velocity, which is a known risk factor for shoulder and elbow injuries. Future studies should incorporate pitch velocity measurements to elucidate the relationship between shoulder external rotation, pitch velocity, and injury risk. Finally, we did not collect data on injury severity or the specific locations of shoulder and elbow pain, as previous studies^14-16,18 using similar methodologies also lacked these detailed assessments. While no participants underwent surgery during the follow-up period, future studies should include detailed evaluations of pain location and severity to better characterize these injuries.

Conclusion

We demonstrated that increased shoulder ABER is a significant risk factor for shoulder and elbow injuries among left-handed high school baseball pitchers. Pitchers with ABER ≥109° in the dominant shoulder had a 3.3 times higher incidence of shoulder and elbow injury than those with ABER <109°. Follow-up studies should be performed to determine the validity of the ABER cutoff values.

Authors

Hitoshi Shitara, MD, PhD (Department of Orthopaedic Surgery, Gunma University Graduate School of Medicine, Maebashi, Gunma Prefecture, Japan); Tsuyoshi Tajika, MD, PhD (Department of Orthopaedic Surgery, Gunma University Graduate School of Medicine, Maebashi, Gunma Prefecture, Japan); Tsuyoshi Ichinose, MD, PhD (Department of Orthopaedic Surgery, Gunma University Graduate School of Medicine, Maebashi, Gunma Prefecture, Japan); Tsuyoshi Sasaki, MD, PhD (Department of Orthopaedic Surgery, Gunma University Graduate School of Medicine, Maebashi, Gunma Prefecture, Japan); Noritaka Hamano, MD, PhD (Department of Orthopaedic Surgery, Gunma University Graduate School of Medicine, Maebashi, Gunma Prefecture, Japan); Masataka Kamiyama, MD (Department of Orthopaedic Surgery, Gunma University Graduate School of Medicine, Maebashi, Gunma Prefecture, Japan); Ryosuke Miyamoto, MD (Department of Orthopaedic Surgery, Gunma University Graduate School of Medicine, Maebashi, Gunma Prefecture, Japan); Kurumi Nakase, MD (Department of Orthopaedic Surgery, Gunma University Graduate School of Medicine, Maebashi, Gunma Prefecture, Japan); Fukuhisa Ino, MD (Department of Orthopaedic Surgery, Gunma University Graduate School of Medicine, Maebashi, Gunma Prefecture, Japan); Takuma Kachi, MD (Department of Orthopaedic Surgery, Gunma University Graduate School of Medicine, Maebashi, Gunma Prefecture, Japan); Yuhei Hatori, MD (Department of Orthopaedic Surgery, Gunma University Graduate School of Medicine, Maebashi, Gunma Prefecture, Japan); Koichiro Yanai, MD (Department of Orthopaedic Surgery, Gunma University Graduate School of Medicine, Maebashi, Gunma Prefecture, Japan); Atsushi Yamamoto, MD, PhD (Department of Orthopaedic Surgery, Gunma University Graduate School of Medicine, Maebashi, Gunma Prefecture, Japan); Kenji Takagishi, MD, PhD (Department of Orthopaedic Surgery, Gunma University Graduate School of Medicine, Maebashi, Gunma Prefecture, Japan); and Hirotaka Chikuda, MD, PhD (Department of Orthopaedic Surgery, Gunma University Graduate School of Medicine, Maebashi, Gunma Prefecture, Japan).

Footnotes

Acknowledgements

The authors thank the personnel, players, coaches, and staff of the Gunma Prefecture High School Baseball Federation for their assistance and cooperation in this study.

Final revision submitted December 27, 2024; accepted January 31, 2025.

The authors declared that they have no conflicts of interest in the authorship and publication of this contribution. AOSSM checks author disclosures against the Open Payments Database (OPD). AOSSM has not conducted an independent investigation on the OPD and disclaims any liability or responsibility relating thereto.

Ethical approval for this study was obtained from Gunma University Hospital (identification No. 1003).

ORCID iDs

Hitoshi Shitara

Tsuyoshi Tajika

Hirotaka Chikuda

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