Risk Factors for Elbow and Shoulder Injuries in Adolescent Baseball Players a Systematic Review

Abstract

Studies on the relationship between baseball game loads (practice, training, and contest hours) and shoulder and elbow injuries among high school pitchers are limited. Therefore, this report included 92 male high school baseball pitchers and evaluated their preseason shoulder and elbow weather condition. All participants completed a self-recorded questionnaire regarding baseball load, presence of shoulder pain or elbow pain, or both, and pitching limitations due to shoulder and/or elbow hurting experienced daily to determine the occurrence of injuries and record the baseball load. The optimal load cutoff value was adamant using a receiver operating characteristic curve analysis. Participants were categorized into high-load and low-load groups according to the aforementioned cutoff value. The Kaplan–Meier method was used to obtain time-to-outcome curves, and cox proportional hazards models were used to calculate the hazard ratios for injury rates. The cutoff value of the average baseball load was 324.4 min per mean solar day. A high load (> 5.5 h/mean solar day) led to a 2.6-times greater chance of injuries and 3.3-times earlier occurrence of injuries than a depression load (< five.v h/24-hour interval). Therefore, a loftier load is a risk cistron for shoulder and elbow injuries in high school baseball pitchers.

Introduction

Shoulder and elbow injuries and hurting are major issues for baseball players^1,2,iii. Although many studies have demonstrated the risk factors for baseball-related shoulder and elbow injuries, a contempo systematic review⁴ showed that in that location accept been just 14 prospective cohort studies: viii studies involving professional players (major league and small league), four studies involving loftier school players, and two studies involving youth players.

Amid professional person baseball game players, shoulder external rotation and elbow varus torque at tiptop external shoulder rotation during pitching⁵, high pitch velocity^six, glenohumeral internal rotation deficit (GIRD), shoulder external rotation insufficiency⁷, full shoulder rotation arrears during the preseason, deficits in the supraspinatus during the preseason, and prone external rotation (PER) force^viii are risk factors for shoulder and elbow injuries. Shitara et al.⁹ showed that, amid high school baseball players, GIRD and greater differences in prone external rotation strength of the arms increased the take a chance for shoulder and elbow injuries. Tyler et al.¹⁰ showed that shoulder and elbow injury risks were not increased for pitchers who experienced an excessive loss of internal range of motion (ROM) or loss of total shoulder ROM, and that only supraspinatus weakness during the preseason was significantly associated with major injuries. Amidst youth baseball players, meaning risk factors for elbow injuries were a history of elbow hurting¹¹, age 9–11 years^xi, playing the position of pitcher or catcher¹¹, pitching more than 100 innings in a yr¹², and preparation more than than 16 h per week^eleven.

As described, evidence of preseason risk factors, such as ROM and strength measured during the preseason, is relatively sufficient; however, evidence of in-flavour chance factors, such as the number of innings played and external load (practice, training and competition hours), is limited. In particular, there is no evidence of the relationship between the baseball game load elapsing and the incidence of shoulder and elbow injuries among high school baseball pitchers.

For adolescent pitchers, gamble factors are related to the number of innings pitched in the games and the duration of practice. The grooming elapsing affects adolescent pitchers more than than established baseball game pitchers, such as college and professional person pitchers. This may be considering adolescent baseball pitchers spend more time with not-pitchers and appoint more than in daily practices, including warming up, batting, pitching, defensive drilling, cooling down, and forcefulness workouts, than practice for pitcher-specific exercises. Additionally, measuring the duration of the baseball load is easier than counting the number of pitches or innings. If pitchers' ain measurement of a high baseball load is related to shoulder and elbow injuries, a simple self-assessment of the full duration of practice, preparation, and game time will contribute to preventing injuries.

Nosotros hypothesized that the high amount of baseball load (preparation and competition hours) in boyish baseball pitchers induced shoulder and elbow injuries. To test the hypothesis, we prospectively investigated the relationship between the baseball game load, defined equally the full duration of daily squad practise, including warming up, batting, pitching, defensive drills, cooling downwardly, strength workouts, and games of high school baseball pitchers and the incidence of shoulder and elbow injuries.

Results

Receiver operating characteristics (ROC) analysis

The ROC analysis showed that the cutoff value of the average baseball load was 324.4 min per day (P = 0.x; surface area nether the curve (AUC) = 0.sixty, Fig. 1).

Baseline characteristics

The average duration of games and practice per calendar week were 452 and 1259 min (7 h 32 min and 20 h 59 min), respectively. Similarly, the average duration of games and practice per mean solar day were 395 and 260 min (6 h 35 min and four h 46 min), respectively. Based on the cutoff value, participants were categorized into the high baseball load grouping (loftier group) and the low baseball game load group (low grouping). There were 16 and 76 pitchers in the high group and depression group, respectively. The preseason baseline assessment indicated no significant difference between both groups regarding baseball game experience, height, weight, ROM of ABIR and ROM of horizontal adduction (HA) in the dominant shoulder, elbow flexion and extension on the dominant side, PER and prone internal rotation (PIR) in the dominant shoulder, and PER and PIR ratios (Table 1). Thus, co-ordinate to these preseason measurements, participants in the ii groups had the same adventure of experiencing shoulder and elbow injuries during the season.

Table 1 Baseline characteristics of the written report participants.

Full size tabular array

Fourth dimension-to-event analysis

The injury charge per unit of the high group was 62.5% (n = 10); still, it was 28.9% (n = 22) for the depression group. The median time to injury was 92 and 28 days for the low and high groups, respectively (Fig. 2). This suggested that a high baseball game load led to a 3.3-times earlier occurrence of injuries. The Kaplan–Meier analysis yielded a risk ratio (Hr) of two.603 for the high group (Table 2). A log-rank test showed that the injury incidence was significantly lower in the low grouping than in the loftier grouping (P = 0.009) (Fig. two). Additionally, injuries occurred 3.3-times before in the loftier grouping than in the low grouping.

Table 2 Results of the Cox proportional hazards model.

Total size table

Post hoc power assay

A post hoc power analysis showed that the statistical power of this study was 0.831.

Discussion

The most important finding of this study was that a high baseball load (> five.5 h per day) for high school baseball game pitchers significantly increased the risk of shoulder and elbow injuries. Furthermore, our results demonstrated that a high baseball load led to a 2.6-fold greater risk of injuries and 3.3-times earlier occurrence of injuries. No previous prospective study of high schoolhouse pitchers has provided evidence that an excessively loftier baseball load induces shoulder and elbow injuries. Therefore, this bear witness may help determine the appropriate baseball load necessary to forbid shoulder and elbow injuries in youth pitchers.

Training and competition hours as an external load

A baseball load of more than five h a day is considered high, exceeding the common load in the United States. However, boyish Japanese baseball players often perform baseball practice not only afterward schoolhouse but also in the morning before school classes begin; thus, the baseball load sometimes exceeds 5 h.

Takagishi et al.³ performed a retrospective nationwide survey of junior high schoolhouse baseball players and demonstrated that there was no significant relationship between the total number of hours of practice per calendar week, the full number of days of do per calendar week, and the presence of shoulder hurting and elbow pain. Only i previous prospective written report demonstrated that preparation more than than xvi h per week¹¹ is a meaning run a risk factor for shoulder pain and elbow hurting in youth players.

Matsuura et al.¹¹ reported that youth baseball game players who trained more than 16 h but 36 h or less per week were at significantly high risk for shoulder pain and elbow pain compared to those who trained 10 h or less per week (odds ratio = 2.00 and odds ratio = 2.33, respectively). This evidence is important for protecting young baseball players from preventable shoulder and elbow injuries. However, unfortunately, there were several limitations to the report by Matsuura et al.^eleven. Beginning, baseline conditions, such as GRID, total ROM in the shoulder, musculus strength, and scapular dyskinesia, were unclear in the pain and non-pain groups because physical examinations were not performed during the study. Second, in that location might have been recall bias due to vague memory because immature participants, including vi-year-old players, were asked to recount their history of shoulder pain and/or elbow pain. Third, in that study, hurting was defined as "present" if information technology restricted participation in baseball for 1 24-hour interval or more; this definition seemed also restrictive for a written report investigating risk. It is difficult to directly compare the present study with that by Shitara et al.⁹ because the definitions of shoulder and elbow injury events are different; our cutoff value of the average baseball game load was calculated as 37.8 h per week (324.four min × 7 days), and our baseball load for high schoolhouse pitchers was longer than theirs for youth baseball game players. In this study, we performed physical examinations to confirm no significant divergence between the baseline weather condition of the high grouping and depression group. Additionally, the participants were asked to record their baseball game load daily to avoid recall bias. Finally, our definition of "shoulder or elbow injury" was whatsoever condition resulting in the pitcher being considered disabled for 8 days or more, which was applied in previous studies^9,13,14 and, therefore, might be more meaningful for investigating risk factors. By addressing the issues of the previous written report, we demonstrated that a high baseball game load (> five.5 h) led to a ii.half dozen-times greater hazard of injuries and 3.3-fold earlier occurrence of injuries compared to a depression baseball game load (< five.5 h), even when there were no significant differences in the baseline characteristics of the groups.

Physical findings and external load

Møller et al.^xv investigated the relationship between shoulder injury and a handball load (grooming and contest hours) of more than 31 weeks for handball players (historic period, 14–18 years); they reported that a lx% increase in the handball load could increase the shoulder injury rate, even for players with normal shoulder characteristics. Moreover, they reported that, compared to players with normal scapular command and external rotational strength, players with scapular dyskinesis and reduced external rotational strength during the preseason were predisposed to shoulder injury when the handball load was moderately increased¹⁵. These findings suggest that reduced external rotational force or scapular dyskinesis enhanced the effect of the external load on the injury rate. Because reduced external rotational force among high schoolhouse pitchers⁹ and professional pitchers^eight and scapular dyskinesis among collegiate baseball game players¹⁶ are known run a risk factors for shoulder and elbow injuries, excessive external load during the season might exacerbate scapular role. Therefore, external rotation of the shoulder might induce injuries. Further studies are needed to analyze these relationships.

Limitations

This study had some limitations. Get-go, information regarding other external load factors, such as the total number of pitches and the number of innings pitched, were not nerveless during this study. These factors might be correlated with training and competition hours and could exist confounding. Although information technology is a study limitation, baseball load is a more comprehensive gene to consider for its contribution to baseball practice and games, rather than the number of pitches or innings. Therefore, nosotros measured the baseball load instead of the number of pitches or innings. Furthermore, all practices and game plans of the participants were mainly managed by the team instead of individuals because all high school baseball players in Japan belong to their school's teams. Therefore, participants spend well-nigh equal time doing baseball practice and grooming as a team activity (which we collected in this study) as they practise individual concrete training or baseball game exercise. All the same, it is a limitation that nosotros did not collect the details of the baseball game load.

Additionally, information technology is difficult to employ the evidence in this study to baseball players in other countries because the environment surrounding baseball game is different across countries. Therefore, this should be considered carefully in future studies. Second, the sample size was relatively small considering the incidence of shoulder and elbow injuries was relatively low for high school baseball pitchers. Nevertheless, the postal service hoc ability analysis showed that the statistical power of the study was 0.831, indicating that the sample size was sufficient for testing the relationship between the external load and shoulder and elbow injuries. Third, it remains unclear how the increased baseball load induced a high injury rate because we did non perform a physical examination or imaging study when the injury occurred. Fourth, there is a possibility for selection bias considering we excluded pitchers performing musculus-specific rotator cuff exercises or posterior capsular stretching exercises outside of those performed during squad exercises. Although we aimed to reduce the bias by selecting interventions, which were reported to reduce shoulder and elbow injuries amid loftier school baseball game pitchers, the selected participants may be at higher risk for these injuries. Notwithstanding, we believe that the result was minimal because we continuously recommended all teams to perform general concrete workout exercises, such as whole-body stretching and strength grooming, as a team exercise, and no pitcher was excluded for this criterion. Finally, the human relationship betwixt the severity of injuries and the baseball load is unclear considering we did non collect data regarding injury severity.

Conclusion

For high schoolhouse baseball pitchers, a high baseball load (> 5.5 h/day) led to a 2.6-times greater gamble of injuries and 3.three-times earlier occurrence of injuries compared to a depression baseball game load (< 5.5 h/twenty-four hours). Although this show requires validation in time to come studies, it may assistance to provide guidelines for preventing injuries among youth baseball pitchers. These results tin be used to establish the basis for discussing the appropriate baseball load to forbid injuries considering the evidence indicated that a high baseball load is a risk gene for shoulder and elbow injuries among high school baseball game pitchers.

Methods

Participants

Preseason medical examinations were performed for 131 high school male person baseball game pitchers between the ages of fifteen and 17 years. Afterwards, informed consent was obtained from the parents of the participants. Finally, 92 pitchers were enrolled in this report.

Following the inclusion criteria of a previous written report⁹, a pitcher was included in our study if he participated in preseason workouts equally an active pitcher and experienced no pitching activity restrictions. In dissimilarity, the exclusion criteria were as follows: prior injuries (e.g., fracture) of the throwing arm; disability to throw or restricted pitching activity considering of a shoulder or elbow problem; or involvement in daily muscle-specific rotator cuff grooming exercises or posterior sheathing/sleeper stretches other than those performed during squad exercises. The Institutional Review Board of Gunma University Hospital (identification number 1003) approved this study. All methods were performed in accordance with relevant guidelines and regulations.

Medical examinations

Every bit previously reported^9,13, preseason baseline medical examinations were performed to evaluate the preseason condition of the participants' shoulders and elbows. The paw dominance of the participants was unknown to the examiners. Baseball experience, height, weight, shoulder ROM, elbow ROM, and shoulder muscle strength were evaluated.

ROM measurements

As previously reported^9,13, shoulder ROM of xc° of abducted internal rotation (ABIR) and HA and elbow ROM of flexion and extension were measured by a certified orthopedic surgeon using a digital protractor (iGaging, Los Angeles, CA, U.s.).

The intra-rater validity and reliability of the ROM measurements using a digital protractor have been established by a previous written report⁹. Passive ROM of ABIR was measured in the supine position with stabilization of the scapula past applying a posterior force to the coracoid process. When measuring ABIR, a digital protractor was placed on the forearm. Passive ROM of HA was measured in the supine position with stabilization of the axillary border of the scapula. When measuring HA, a digital protractor was placed on the humerus. Similarly, passive ROM of elbow flexion and passive ROM of the extension were measured in the supine position.

Strength measurements

PIR strength and PER forcefulness of the shoulder were measured using a PowerTrack II Commander hand-held dynamometer (J-Tech Medical, Salt Lake City, UT, Us) by a certified orthopedic surgeon, as previously reported^8,ix,13. The intra-rater validity and reliability of manus-held dynamometers have been established in a previous study⁹. The median value of the iii repetition trials was recorded and subsequently analyzed. PER was measured in the prone position with the humerus in 90° of abduction and the elbow in 90° of flexion. The arm was set in a neutral position, and the examiner stabilized the humerus. Participants were asked to rotate the arm externally with maximum power confronting the dynamometer placed on the dorsal side of the forearm, 5 cm proximal to the proximal wrist extension crease. PIR was measured similarly, except that the dynamometer was placed on the volar side of the forearm, five cm proximal to the proximal wrist flexion crease. Similarly, participants were asked to internally rotate the arm with maximum ability. The dominant-to-nondominant ratios of PER and PIR were calculated for each participant and analyzed.

Injury tracking and season information collection

Shoulder- and elbow injuries were divers every bit any condition resulting in the pitcher beingness considered disabled for 8 days or more than^ix,13,xiv. Other injuries that occurred via other mechanisms, such as trauma from falls, collisions with other players, sprains while running, or being hit past a pitch, were non included in the statistical analyses. To detect when injuries occurred and tape the exact baseball load, participants were asked to complete a cocky-recorded questionnaire regarding baseball load, the presence of shoulder pain or elbow pain, or both, and limitations to pitching caused by shoulder pain or elbow pain. To avoid recall bias, participants completed the questionnaire daily and returned the record to us monthly. Furthermore, nosotros called the participants once or twice each month to verify that they were completing the daily questionnaires.

Statistical analysis

We performed statistical analyses using SAS 9.4 (SAS Constitute Inc., Cary, NC, United states). All tests were 2-sided with a significance level of P ≤ 0.05. A receiver operating characteristic (ROC) curve analysis was performed to detect the cutoff value of the baseball load. Subsequently, participants were categorized into two groups using the detected cutoff value based on the Youden index. The Isle of mann–Whitney U test was used to evaluate grouping differences. The Kaplan–Meier method was used to obtain time-to-issue curves, and HRs for the incidence of injury were calculated using Cox proportional hazards models. A log-rank test was performed to compare the survival distributions betwixt groups.

To calculate the required number of participants, nosotros performed an a priori statistical power assay, which indicated that we needed 39 participants to accomplish a statistical power of fourscore% at an α level of 0.05 with an HR of 2.7⁹, an accrual interval of 150 days, a follow-upwards interval of 150 days, and a median time to failure for each group; the shortest time to failure was 50 days according to the Kaplan–Meier assay¹⁷. After data collection, nosotros performed a postal service hoc power analysis to evaluate the statistical ability of this report.

Data availability

The data supporting the findings of this study are bachelor on request from the respective writer H.South. The data are not publicly available because they comprise data that could compromise the privacy of research participants.

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Acknowledgements

We would like to thank the personnel, players, coaches, and staff of the Gunama High School Baseball game Federation for their assist and cooperation in this study. Also, we would similar to give thanks Kureha Special Laboratory Co., Ltd. for assistance with statistical analysis. This inquiry was partly supported by Grants from the Nihon Sports Medicine Foundation 2012 and Kozuki Foundation 2012 to H.S and a Grant from the Japanese Orthopedic Order for Sports Medicine to TI.

Funding

This inquiry was partly supported by Grants from the Nippon Sports Medicine Foundation 2012 and Kozuki Foundation 2012 to H.S and a Grant from the Japanese Orthopedic Society for Sports Medicine to TI.

Author information

Affiliations

Department of Orthopaedic Surgery, Gunma Academy Graduate School of Medicine, 3-39-22, Showa, Maebashi, Gunma, 371-8511, Nihon

Hitoshi Shitara, Tsuyoshi Tajika, Takuro Kuboi, Tsuyoshi Ichinose, Tsuyoshi Sasaki, Noritaka Hamano, Takafumi Endo, Masataka Kamiyama, Daisuke Simoyama, Junki Suzuki, Atsushi Yamamoto, Tsutomu Kobayashi, Kenji Takagishi & Hirotaka Chikuda

Contributions

H.S., T.T., A.Y., 1000.T., and H.C. conceived and designed the experiments. H.S., T.T., T.K., T.I., T.South., N.H., T.Eastward., One thousand.K., D.S., J.Due south., A.Y. and T.K. performed the experiments. H.S., Northward.H. and J.Southward. analyzed the data. H.South. wrote the paper. H.S., T.T., T.K., T.I., T.S., Northward.H., T.E., A.Y., T.K., 1000.T. and H.C. recruited the participants. All authors reviewed and approved the last version of the newspaper.

Corresponding author

Correspondence to Hitoshi Shitara.

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The authors declare no competing interests.

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Shitara, H., Tajika, T., Kuboi, T. et al. High baseball loads induce shoulder and elbow injuries among loftier schoolhouse baseball game pitchers: a prospective study. Sci Rep 11, 351 (2021). https://doi.org/10.1038/s41598-020-79841-7

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Received: 15 April 2020
Accustomed: 14 December 2020
Published: 11 January 2021
DOI : https://doi.org/10.1038/s41598-020-79841-seven

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