Shoulder Injury Incidence and Epidemiology in Youth, High School, and Collegiate Fastpitch Softball Players: A Systematic Review and Future Research Perspectives

Abstract

Context:

Fastpitch softball is one of the most popular sports in the United States among young female athletes. Softball players regularly subject their shoulders to extreme range of motion and high velocity movements. To date, no systematic review has reported on the epidemiology and incidence of shoulder injuries in softball players.

Objective:

To describe the incidence and epidemiology of softball-related shoulder injuries in youth, high school, and collegiate female softball players.

Data Sources:

PubMed, Web of Science, and Embase were searched for relevant English language articles from 1980 to 2023.

Study Selection:

Studies selected based on predefined inclusion criteria. Studies were required to be available full text, in English.

Study Design:

Systematic review.

Level of Evidence:

Level 4.

Data Extraction:

A preliminary screening was performed based on study title and abstract. In the subsequent screening, the full text versions of the remaining articles were evaluated by 2 reviewers for the fulfillment of the inclusion criteria.

Results:

A total of 7 articles met criteria for inclusion. All studies evaluated injuries among softball players for at least 1 season. In total, there were 1107 softball-related shoulder injuries reported in the 7 studies included in this systematic review. Of the 3 studies that included a shoulder injury rate, a mean rate of 4.01 shoulder injuries per 10,000 athlete-exposures was calculated. The 2 most common shoulder injuries were shoulder muscle-tendon strains (297) and shoulder/biceps tendinitis (220).

Conclusion:

High-level prospective studies reporting injury incidence and risk factors among female softball players are extremely limited. Only 2 studies eligible for inclusion in this systematic review were prospective in nature, with neither of these reporting the specific injury rate for shoulder injuries among softball players.

Fastpitch softball is a popular sport among female youth and collegiate athletes, with >2 million athletes playing in the United States today.^16,19,24 Participation in softball among youth and high school athletes has increased consistently year to year, approaching that of baseball, according to the National Federation of State High School Associations. ¹³ With increasing participation in fastpitch softball over the past several decades, the number of softball-related shoulder injuries presenting to sports medicine physicians and orthopaedic surgeons is also expected to increase. Shoulder injuries can be debilitating for softball players and may result in significant practice or competition time loss and long-term shoulder discomfort and pain. Although there are several studies reporting epidemiology and risk factors for shoulder injuries in baseball, there is a paucity of available literature investigating softball-related shoulder injuries in both pitchers and position players.

Although it is commonly thought that the windmill pitching motion seen in fast-pitch softball is inherently less strenuous on the pitcher’s arm compared with conventional overhead pitching in baseball, a biomechanical analysis by Werner et al ³⁰ has previously disputed this. The mean degree of shoulder distraction stress on softball pitchers as measured during the 1996 Olympic Games was found to be 80% ± 22% of their bodyweight, comparable with that of baseball pitchers (mean = 108% ± 16% bodyweight).^10,29,30 Although softball and baseball share several key similarities, their differences may be important to note when considering shoulder injury risk. The size and weight of the ball used, distance between bases, pitching mound distance, pitching mound height, field size and surface, and number of innings all typically differ between baseball and softball.^12,14 Furthermore, the underarm pitching technique utilized in fastpitch softball has been shown to place increased load on the shoulder rather than the elbow, leading to an increased rate of shoulder injuries among youth softball pitchers, whereas elbow injuries are more commonly seen in youth baseball players and pitchers.^4,5 Thus, a specific investigation regarding the incidence and epidemiology of shoulder injuries among female softball players is needed to identify risk factors and to help elucidate injury patterns and prevention strategies.

Current studies reporting injury incidences, risk factors, and epidemiology of softball injuries—particularly shoulder injuries—are extremely limited. Due to this knowledge gap, orthopaedic and sports medicine specialists often extrapolate from data that are published from baseball literature, despite critical differences in the 2 sports. Therefore, the purpose of this study was to perform a systematic review of the literature to determine the incidence and epidemiology of softball-related shoulder injuries in youth, high school, and collegiate female softball players. We hypothesized that a higher prevalence of shoulder muscle strains and tendinitis versus labral pathology would be observed in softball players.

Methods

Information Sources

A systematic review of the literature describing softball injury incidence was conducted according to the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines and the guidelines of Harris et al ⁶ outlining the proper procedure for conducting a sports medicine systematic review. This review was registered in the PROSPERO systematic review registration system. Three databases (PubMed, Embase, and Web of Science) were searched to identify studies that included data on the epidemiology and incidence of shoulder injuries in softball players. Language was restricted to English, but date of publication was not restricted due to the limited published research investigating the topic of this review. PubMed, Embase, and Web of Science were searched using the keywords “softball,” “shoulder,” “injury,” and “prevalence” and the Boolean “AND/OR” operators. Full details for the electronic searches are available in Appendix Table A1, available in the online version of this article. Search results were imported into a reference manager (Mendeley) for removal of duplicate articles. All studies were assigned a level of evidence of Level 4 due to the nature of epidemiological surveillance injury reports.

Eligibility Criteria and Study Selection

Two reviewers screened eligible studies in a 2-step process. In step 1, the reviewers evaluated titles and abstracts of all studies resulting from the database searches described above. Title and abstract screening were based upon the predefined inclusion and exclusion criteria. Inclusion criteria were (1) original research studies (prospective or retrospective in nature), (2) description of incidence or epidemiology of softball-related shoulder injuries, and (3) description of level of softball competition (ie, youth fastpitch, high-school fastpitch, collegiate fastpitch, etc). Exclusion criteria were (1) studies that did not investigate shoulder injuries (eg, elbow injuries; studies describing “upper extremity” injuries rather than specifically the shoulder); (2) studies that did not include softball players; (3) studies that included softball players but did not differentiate from other athletes/sports; (4) articles not written in English; (5) articles not available in full text; and (6) case reports, review articles, or biomechanical studies. Study title and abstract screening were performed for references of studies resulting from the initial search. All titles and abstracts were evaluated independently by 2 reviewers. In cases of disagreement, a third reviewer made the final decision for initial article inclusion or exclusion. In step 2, 2 reviewers evaluated the full-text versions of included articles to confirm eligibility for this review, and a third reviewer confirmed these studies met the criteria for inclusion.

Data Collection

Data were compiled in Excel (Microsoft). Data extracted from the selected articles included the following: study title, author names, publication year, study design, sample size, study period, description of the study population, injury definition, overall incidence of softball shoulder injuries, reported risk factor (if specified), and statistical measurement of injury risk (if specified). Statistical measures were reported as expressed by the original authors: shoulder injury rate, hazard ratio, odds ratio, and relative risk. Because of limited available literature on this topic and significant study heterogeneity, a true quantitative synthesis was not possible.

Risk of Bias Assessment

Risk of bias was assessed with a modified version of the Newcastle-Ottawa Scale (NOS).^7,28 This scale was chosen after consideration of the advantages and disadvantages of available methods for evaluating bias and was modified using similar adaptations described by Saragiotto et al. ²² A full description of modified criteria can be found in the description following Appendix Table A2, available online.

Articles could be awarded a maximum of 1 star for each item, except for item 1, which could be awarded a maximum of 2 stars. This criterion was modified to include up to 2 stars to assess whether a study’s injury data were delineated based on position (ie, pitcher versus position player). Studies that included a description of the type of softball players investigated (ie, youth, collegiate, etc) were given 1 star, and studies that included this description in addition to delineating between pitchers and position players were given an additional star for a potential of 2 stars. Thus, a maximum of 8 stars could be given to the articles. Risk of bias assessment was conducted independently by 2 reviewers. Of note, the 2 independent reviewers did not differ by >1 star for any individual study, with final determination being made by a third independent reviewer.

Results

A total of 514 articles were identified in the database search. Of those, 109 were duplicates appearing in >1 database and were thus removed. Duplicates were identified by the reference program Mendeley Reference Manager and confirmed by 2 independent authors. After initial title and abstract screening of the resulting 405 studies, 375 nonrelevant studies were excluded. These 375 studies were removed due to lack of injury incidence data, not examining softball-related shoulder injuries, or not having a full-text article available for review. This yielded 30 full-text studies, each of which were reviewed independently against the predefined inclusion and exclusion criteria by 2 separate authors. Four studies were excluded for examining duplicate patient populations from the same author group as a separate study included in this systematic review. In the cases of duplicate investigation populations, the study that contained a greater number of patients, longer follow-up, or more thorough analysis of shoulder injuries was selected for inclusion in this systematic review. After full-text review, 7 studies were deemed eligible for this systematic review and included in the final analysis.^{8,10,17,23-25,27} Full eligibility details can be found in the PRISMA flow diagram in Figure 1. Study characteristics of each of the included studies can be found in Table 1, and shoulder injury data are presented in Appendix Table A3, available online. There were 4 studies with an NOS score of 6, 2 studies with an NOS score of 7, and 1 study with an NOS score of 8. Complete results of this assessment can be found in Appendix Tables A2 and A4, available online.

Figure 1.

PRISMA flow diagram. PRISMA, Preferred Reporting Items for Systematic Reviews and Meta-Analyses.

Table 1.

Basic study overview and characteristics

Author (Year)	Country	Population/Age Group	Study Design	Observational Time Period
Veillard et al 27 (2021)	United States	Collegiate softball players	Descriptive epidemiological	2014-2015 through 2018-2019 academic years
Snyder Valier et al 25 (2020)	United States	Secondary school girls’ softball players	Descriptive epidemiological	2011-2012 through 2013-2014 academic years
Oliver et al 17 (2019)	United States	High school softball players	Descriptive epidemiological	2005-2006 through 2016-2017 academic years
Hibberd et al 8 (2016)	United States	Collegiate softball players	Descriptive epidemiological	2009-2010 to 2014-2015 academic years
Smith et al 24 (2015)	United States	Youth fast-pitch softball players (median age, 14 years; range, 9-18)	Prospective observational cohort	Between January 2011 and March 2011 and before softball season
Marshall et al 10 (2007)	United States	Collegiate softball players	Descriptive epidemiological	1988- 1989 to the 2003-2004 seasons
Shanley et al 23 (2011)	United States	High school softball players	Prospective observational cohort	During the 2009 softball season

The year of publication of the included studies ranged from 2007 to 2021, and all studies represented fastpitch softball athlete populations in the United States. The time range of investigations for injury observation in the included studies ranged from the 1988-1989 academic year to the 2018-2019 academic year.^10,27 Across the included studies, the primary purpose was to describe and report the basic epidemiology of various injuries experienced by youth, high school, and collegiate athletes. Three studies reported injury data in collegiate softball players,^8,10,27 1 study reported injury data on select-level softball players (age range, 9-18 years), ²⁴ and 3 studies reported injury data on high school or secondary school female softball players.^17,23,25

The total number of softball-related shoulder injuries among the 7 included studies was 1107. It was not possible to report an overall number of players observed as only 2 included studies were prospective in nature. Each study’s injury definition is listed in Appendix Table A5, available online. It should be noted that not all of the included studies reported the overall shoulder injury rate or incidence among softball players. Only 3 studies included this measure, with a mean rate of 4.01 shoulder injuries per 10,000 athlete-exposures (AEs) across these 3 studies.^8,17,25 Four studies included a delineation of the number of shoulder injuries sustained in a practice setting versus a competition setting.^8,10,17,27 Of these, there were a total of 614 softball-related shoulder injuries that occurred in practice and 323 injuries that occurred in a competition setting. Of studies that included data regarding type of shoulder injury, there were 297 instances of shoulder muscle/muscle-tendon strains, 220 instances of shoulder/biceps tendinitis, 100 shoulder subluxations, 15 shoulder ligament sprains, 4 acromioclavicular (AC) joint sprains, and 1 shoulder dislocation.^8,10,17,24 Although several studies included a discussion regarding injury time loss, only 2 specifically reported this regarding softball-related shoulder injuries. Among these 2 studies, 24 of the shoulder injuries required the athlete to miss some amount of practice or competition, while the remaining 138 shoulder injuries resulted in no time lost.^24,25 In these studies, no time lost was defined as restricted participation for <24 hours or missing zero games due to the injury.^24,25 In a prospective study of 98 youth fastpitch softball athletes by Smith et al, ²⁴ a breakdown of time loss due to shoulder injuries was reported, with 3 athletes missing the entire season due to a shoulder injury, 1 missing 25 games, 1 missing 6 weeks, 1 missing 2 weeks, 1 missing 1 week, and 1 missing only 1 game. Only 3 of the 7 included studies stratified injury results based on injuries suffered by pitchers versus injuries suffered by nonpitchers. A total of 259 shoulder injuries were reported across these 3 studies, with 50 of them being pitching-related injuries (19.3%).^17,23,24

Discussion

We expected that softball athletes would experience shoulder muscle strains and tendinitis more frequently than labral tears. This was hypothesized due to the underhand pitching style observed in fastpitch softball versus overhead pitching in baseball, as labral tears—particularly SLAP (superior labrum anterior and posterior) tears—are common among overhead athletes like baseball pitchers. ¹¹ Shoulder injuries are common among softball players, and increased participation in softball among young athletes is expected to increase the number of these injuries. The main findings of our study are that muscle strains and tendinitis are the most common injuries among softball players and that there is a significant paucity of literature reporting on the epidemiology of shoulder injuries. These findings highlight that (1) differences in injury patterns and types in softball players versus baseball players may exist; and (2) there is a need for high-level, prospective analyses investigating shoulder injuries among softball players. In this review of 1107 total softball-related shoulder injuries, we found that the 2 injuries reported most frequently were shoulder muscle strains/generalized shoulder pain (n = 306, 27.6%) and shoulder tendinitis (n = 220, 19.9%), followed by shoulder subluxations (n = 100, 9.0%), AC joint sprains (n = 4, 0.4%), and shoulder dislocation (n = 1, 0.1%).

The prevalence of softball-related shoulder injuries may be different from that observed in baseball players. A recent analysis of 3414 shoulder injuries suffered by professional baseball players found that impingement/subacromial bursitis was the second most common injury diagnosis behind rotator cuff injuries. ⁹ However, the present review reported no instances of impingement or subacromial bursitis injuries across the 7 included studies. Although no instances of subacromial bursitis or impingement were found in this review, these injuries likely still exist among softball athletes. The lack of shoulder bursitis and impingement among softball players may be due to inconsistency in injury terminology, as rotator cuff tendinitis and bursitis can often refer to the same pathology. This highlights a challenge of investigating differences between softball and baseball shoulder injury studies, as these studies may utilize different injury descriptions or terminology when they are indeed describing the same pathology. In future research, comprehensive descriptions of each injury type reported may allow for more accurate and definitive injury comparisons. This 2022 study also reported that nearly 10% of all injuries involved labral tears, either reported as anterior instability with labral (n = 235) or SLAP (n = 102) tear. ⁹ This differs from our findings among softball-related shoulder injuries, in which none of the 7 included studies specifically reported instances of labral pathology. Although these studies lacked specific discussion regarding shoulder instability, it again should be noted that a total of 100 softball-related shoulder subluxations were reported, which may in fact be attributed to labral pathology resulting in instability. Thus, softball-related labral injuries may be more common than current literature suggests because of significant variability in injury reporting terminology. In addition, although several of the included studies reported data on game or practice time lost, only 2 stratified this information by injury location and sport.^24,25 One study defined a nontime-loss injury as one that did not restrict an athlete’s participation 24 hours postinjury, ²⁵ whereas the other study defined nontime-loss injuries as those resulting in zero games missed. ²⁴ Between these 2 studies, 138 injuries were classified as nontime-loss, while 24 were categorized as time-loss injuries. However, these studies varied significantly in their criteria for classifying time-loss versus nontime-loss injuries, making it difficult to draw definitive conclusions about the severity of these injuries. Complete injury time loss data are presented in Table A3. Future research consisting of detailed injury descriptions and consistent reporting measures is critical to discuss definitive conclusions of differences between softball and baseball shoulder injuries. This may ultimately assist athletic trainers, physicians, and coaches in developing improvements in treatment and injury prevention strategies.

In a 2022 systematic review, Tramer et al ²⁶ investigated rates of return to play among professional baseball players following injury. Overall, 691 shoulder injuries were identified across 15 studies. A total of 193 baseball-related labral tears were reported (27.9%). However, only 3 studies analyzed in this 2022 systematic review included a specific description of the type of labral tear. Of these 3 studies, there were a total of 47 reported SLAP tears. ²⁶ It should again be noted that while no instances of SLAP tears were specifically reported in the present review of softball injuries, shoulder subluxations and dislocations were reported. Although we suspected that SLAP tears would be more likely to occur in the overhead pitching motion of baseball players, a lack of specific and detailed injury descriptions makes comparison between baseball and softball shoulder injuries challenging. Other notable injuries included AC joint injuries (n = 130, 18.8%) and rotator cuff tears (n = 77, 11.1%). ²⁶ Like the injury analysis discussed above, this study reported a high rate of labral injuries suffered by baseball players. Overall, a comparison of our findings with baseball-related shoulder injuries demonstrates that labral tears and AC joint injuries are commonly observed in baseball players, whereas softball-related shoulder injuries appear to more commonly involve muscle strains or tendinitis.

Literature investigating shoulder injuries among baseball players is significantly more abundant than that of current softball injury literature. This includes prospective analyses and systematic reviews reporting modifiable risk factors for shoulder injuries in baseball players.^1,15,20 In 2019, Agresta et al ¹ systematically reviewed 14 prospective cohort studies to analyze and report risk factors for arm injuries among baseball players. Of the 14 included studies, 9 reported adequate (minimum 80%) follow-up throughout the investigated baseball season. Another systematic review of prospective cohort studies analyzed whether preseason screening of an athlete’s range of motion was associated with the risk of shoulder or elbow injuries among various overhead athletes, including baseball players. ²⁰ Similarly, this study was able to report specific follow-up data from the investigated population, reporting players lost to follow-up and players who were ultimately included in the analysis. ²⁰ Unfortunately, as presented in this current systematic review, prospective analyses with strong follow-up that report softball shoulder injury data and risk factors are extremely limited. As discussed previously, only 2 prospective cohort studies were identified from our search and included in this review. Furthermore, only 337 athletes were examined between these 2 studies, with 1 of these studies combining softball and baseball injuries into 1 cohort. Thus, the combination of limited prospective analyses and significant study heterogeneity among softball shoulder injury literature makes determining risk factors and overall shoulder injury incidence extremely challenging. While similar systematic reviews report injury incidence and independent risk factors for shoulder injuries among baseball players such as pitch velocity, shoulder biomechanics and range of motion deficits, age, training or pitching load, and length of weekly training, the same conclusions cannot be made for female softball players at this time.^{1 -3,15,21}

There are major limitations of this study that should be discussed, many of which are inherent to a systematic review. We analyzed data reported in generally low level of evidence studies with significant heterogeneity in both study design and injury reporting measures. In addition, the small number of studies and required exclusion due to repeated observed populations weaken the findings. Because of the limited data available in the current literature on softball-related shoulder injuries, this review included studies that were exclusively observational epidemiologic injury reports. As a result, these studies could not provide the total number of athletes in the observed cohort or specify the number of athletes lost to follow-up. Furthermore, only 3 of the 7 included studies reported an overall shoulder injury rate. Because of the limited softball injury literature, injury rate reporting was not a requirement for inclusion. This likely limits the generalizability of our reported overall rate of 4.01 shoulder injuries per 10,000 AEs. Because injury definitions, injury classifications, time loss descriptions, position classifications, and statistical reporting are inconsistent between the included studies, study heterogeneity is also a significant limitation of this review. Utilizing the NOS for risk of bias assessment should also be recognized as a potential limitation, as this scale relies on subjective assessment by the authors, does not assess all potential bias risks, and is difficult to apply to a diverse group of study designs. In addition, some studies have reported variable inter-rater reliability.^7,18 Furthermore, because of the limited available studies on this topic, inclusion criteria for this systematic review were lenient to allow the authors to adequately evaluate all potential studies reporting on softball-related shoulder injuries (ie, studies were ultimately included if they contained shoulder injury epidemiological data in youth, high-school, collegiate, or professional softball athletes). Recall bias was a factor in the included studies that involved player-reported method of reporting injuries. Age ranges also varied between studies, with youth, high school, and collegiate softball players all being represented in this systematic review.

Conclusion

While fastpitch softball is becoming an increasingly popular sport among young female athletes, there is a paucity of high-level studies investigating shoulder injury risk factors and incidence in these athletes.