Over the past few decades, organized sports participation has steadily risen together with the incidence of overuse throwing injuries, particularly in baseball (29), although also in javelin, water polo, tennis, softball, and handball. Research on youth throwing injuries in sports outside baseball is limited. The growth of Little League Baseball in the United States may have plateaued, as the organization last reported in 2012 that participation was 6.8% below that in 2008. Despite this, an estimated 15 million children and adults play organized baseball, including 5.7 million children in eighth grade or lower (20). Despite falling numbers of participants, youth baseball has seen a striking rise in year-round participation, single-sport specialization, increased exposure from play in multiple leagues, and performance in showcases (31). It would appear that the number of serious arm injuries in young pitchers has begun to level off since the introduction of recommendations designed to reduce pitching injuries by USA Baseball and other organizations (50). An additional, perhaps alternative, explanation is simply that fewer children participate in organized youth baseball so fewer injuries occur. This explanation becomes more relevant in light of several articles discussed in the following sections that highlight plenty of room for improvement in guideline adherence. Regardless, close to one-third of youth baseball pitchers will experience shoulder or elbow pain. This prevalence increases with age (38).
Dr. Willard Dotter published one of the first descriptions of a pitching injury in a skeletally immature athlete in 1953. His case study discussed a fracture through the epiphysis of the proximal humerus of a 12-year-old pitcher (15). Early recommendations to limit pitching in youth baseball date back to 1966 when Adams suggested an innings count restriction and throwing limitations for young pitchers because of increasing number of reported injuries (1). In 1976, two large surveys attempted to characterize the effects that baseball participation had on the pitching elbow of youth league participants. Gugenheim et al. noted that approximately 17% of participants reported elbow discomfort (23), and Larson et al. showed 20% incidence of elbow complaints (32). By the mid-1990s, most experts believed that to limit these overuse injuries, limitations should be on the number of pitches and not on the number of innings pitched. The American Sports Medicine Institute (ASMI), commissioned by USA Baseball Medical and Safety Advisory Committee (USAB-MSAC), first investigated pitch limits along with additional risk factors with a survey to baseball experts. Unsurprisingly, the number of pitches thrown proved a more important risk factor than the number of innings pitched (6). New specific pitch count guidelines were then introduced by Little League Baseball in 2007, replacing a decade-old guideline that limited pitchers to pitching six innings per week. Subsequent studies have come to similar conclusions (41), and today, the USAB-MSAC along with the ASMI (5), Little League Baseball (36), Baseball Canada (7), and the American Academy of Pediatricians (4) all have recommendations for pitch count limitations based on the age of the athlete (Fig. 1). The recommendations are similar in that pitch count limitations increase with age and recommended rest periods lengthen as the number of pitches per event increases.
Despite almost 50 years of awareness and research into youth overuse throwing injuries, some alarming misconceptions still abound. A 2012 study revealed that 31% of baseball coaches, 28% of players, and 25% of parents do not believe that pitch count is a risk factor for elbow injury. In that same study, 37% of parents, 51% of high school athletes, and 26% of collegiate athletes also believed that “Tommy John surgery” or ulnar collateral ligament (UCL) reconstruction should be performed prophylactically on athletes without elbow injury to improve performance (2). In 2012, Fazarale et al. (18) conducted an internet-based survey to assess whether youth baseball coaches were aware of and were following the recommended guidelines set forth by the USAB-MSAC. Seventy-three percent of coaches reported that they follow the recommendations; however, only 43% of the questions regarding pitch count and rest periods were answered correctly. In addition, only 53% of respondents felt that the other coaches in the league abided by the recommendations. A similar study was performed the following year in Japan by Yukutake et al. (51), with their results indicating that only 40% of coaches had correct knowledge of pitching guidelines.
These data indicate continued need for education and risk assessment for overuse throwing injuries. Hopefully, with better understanding of the mechanisms and risk factors for overuse throwing injuries, adherence to pitch count guidelines will improve. Better adherence together with appropriate treatment of overuse injuries, when they do occur, should allow children to stay healthy and active in a game they enjoy.
Prevalence of Shoulder/Elbow Injuries
Epidemiologic studies on the incidence and prevalence of shoulder and elbow pain related to youth baseball date back decades. Pitchers are 3.6 (45) to 4.5 (25) times as likely to experience an upper extremity injury compared with a position player. Studies examining elbow symptoms alone in youth baseball players have found a prevalence of symptoms ranging from approximately 17% (23) to 26% (38), with approximately 7% of all pitching performances resulting in elbow symptoms. Additionally, nearly 9% of all pitching performances result in shoulder symptoms (37). When looking at youth baseball pitchers alone, between 26% and 35% will experience elbow or shoulder pain each year (38). Furthermore, in 2011, the results of a 10-year prospective study following 481 initially healthy youth pitchers aged 9 to 14 years demonstrated 5% incidence of serious injury resulting in surgery or retirement from baseball (21).
Anatomic and physiologic differences between the mature and developmentally immature skeleton include increased bone plasticity, ligamentous laxity, open epiphyseal growth plates, and underdeveloped musculature (27). These factors are hypothesized to contribute to the risk of adolescent injury. Risk factors regardless of age include throwing mechanics (13), total exposure, and pitching while fatigued (41).
An adolescent athlete’s bones are able to absorb more energy before fracture and therefore have increased capacity to undergo bone remodeling when compared with mature bones. The large external rotation moment placed on the proximal humeral physis in late cocking results in bony growth in the direction of humeral retroversion. Retroversion is the angle between a line drawn through the humeral epicondyles and a line bisecting the articular margins of the humeral head at the anatomical neck. Studies have shown a 14° and 17° increase in humeral retroversion when comparing the dominant and nondominant shoulder in professional handball (42) and baseball pitchers, respectively. These athletes are typically asymptomatic. In fact, some authors have described this rotational motion change as a beneficial adaptation (44). The increased humeral retroversion allows increased external rotation, with decreased tension being placed on anterior soft tissues that may decrease the risk of injury. Also, an increase in external rotation will allow an increased angle for which the ball can be in the acceleration phase, with a theoretical increase in pitching velocity (34).
The shoulder has demonstrated increased laxity in adolescents compared with adults and could be the result of a greater proportion of type III to type I collagen seen in children (48). Increased laxity and microinstability have been implicated in pathology such as internal impingement.
The relatively weak epiphyseal growth plate is particularly vulnerable during periods of long bone growth. The epiphyseal plate is most resistant to tension and least resistant to torsion and poorly tolerates the biomechanical stress imposed by high-velocity throwing (35). Repetitive trauma typically results in physeal injuries in adolescents as opposed to ligamentous injuries in adults (34).
It is hypothesized that, compared with adults, children are substantially less capable of recruiting or fully using their higher-threshold, type II motor units. In addition, children have lower size-normalized maximal voluntary force, speed, and power than adults (14). These differences become particularly relevant in light of a study by Trakis et al. (46) who found that weakness in muscles of the posterior shoulder in the throwing arm of adolescent pitchers compared with the nonthrowing arm was substantial in adolescents with pain.
Furthermore, in cadaveric studies, the UCL has been directly measured to fail between 22.7 and 33 N·m while 120 N·m of peak valgus torque has been measured at the elbow of experienced overhead throwers (3). Although most of this discrepancy can be explained by flexor-pronator muscle activation as a dynamic elbow joint stabilizer, youth pitchers with relatively decreased muscle strength may place more force through the epiphyseal plate and further predispose to injury.
With the exception of some data that youth pitchers have improper timing with trunk rotation, the kinematics of pitching is generally similar for both youth and elite adult pitchers (30). However, joint forces and torques increase with age and levels of competition. Maximum anterior force present during the cocking phase has been found to be approximately twice as high in professional pitchers (33.8 N·kg−1) as compared with youth pitchers (16.2 N·kg−1) (43). Poor pitching mechanics have been associated with shoulder injury. One biomechanical study did indeed show decreased humeral internal rotation torque and increased efficiency with proper mechanics (13), suggesting that pitchers should learn proper throwing mechanics as early as possible.
The kinematics of various pitch types differ, but despite this, velocity may be the single most important risk factor when it comes to risk of injury and pitch type. In a study by Dun et al. (16), elbow and shoulder loads were greatest in the fastball and least in the change-up, with the curveball producing midrange loads. Additionally, Nissen et al. (40) examined adolescent pitchers with 2 years of experience to assess differences of various pitches and found that lower moments at the shoulder and elbow existed when throwing the curveball versus the fastball. Despite lack of evidence, the position statement for youth baseball from the ASMI, based on expert opinion, expresses concern over throwing curveballs too early since this may impede mastering proper pitching mechanics (5). Olsen et al. (41) retrospectively examined risk factors associated with the need to undergo shoulder or elbow surgery in adolescent baseball players. Pitching with higher velocity was shown to be present in the injured group. The mean self-reported fastball in the injured group was 88 mph compared with 83 mph in the uninjured group. Even more importantly, pitching with a fastball speed of greater than 85 mph increased the injury risk by 2.58 times.
In a retrospective study of 140 adolescent pitchers aged 14 to 20 years (41), multivariable logistic regression comparing the uninjured group with those requiring surgery found that averaging more than 80 pitches per game almost quadrupled the chance of surgery (odds ratio, 3.83) and pitching competitively more than 8 months per year increased the odds of surgery by fivefold (odds ratio, 5.05). Most alarming was the finding that a pitcher who regularly pitched with his arm fatigued was 36 times as likely to be in the surgery group. Fatigue also has been shown to impair proprioception and potentially contribute to risk of injury (47).
Recent prospective studies also have identified overuse as a principle risk factor for pitching injury. In a 10-year ASMI study looking at 9- to 14-year-old pitchers (21), pitching more than 100 competition innings in a calendar year more than tripled the risk of serious elbow or shoulder injury. In that study, pitchers who also played catcher were 2.7 times more likely to suffer a serious injury than a pitcher who did not catch.
Little Leaguer’s shoulder
The developing physis is the weak link implicated in pediatric shoulder pathology. The growth plate is weakest to torsional stress and is most susceptible to injury during periods of rapid growth commonly seen during puberty. Most chronic shoulder injuries thus occur in throwing athletes between the ages of 13 and 16 years (22). Little League shoulder refers to an epiphyseal widening caused by rotational stress placed on the proximal humeral epiphysis during overhead throwing and is medically referred to as an epiphysiolysis.
Patients with Little League shoulder will typically present with diffuse shoulder pain aggravated with throwing. History suggests recent increase in their throwing regimen. Examination findings include tenderness over the anterolateral aspect of the shoulder, with weakness to abduction and internal rotation that may mimic rotator cuff injury. There may be a glenohumeral internal rotation deficit (34). Radiographic imaging should include an axillary and AP radiograph with the shoulder in 30° of external rotation and comparative contralateral views. Radiographic findings typically include physeal widening and also may demonstrate metaphyseal sclerosis, osteopenia, and fragmentation (12).
Treatment involves complete rest from throwing until symptoms resolve, typically 2 to 3 months. Following this, patients should undergo a progressive throwing program as part of their physical therapy with slow increase in velocity and distance. Emphasis should be on proper throwing mechanics with rotator cuff strengthening and scapular stabilization as well as capsular stretching. On review of 23 cases of Little League shoulder treated conservatively with an average of 3 months of rest from throwing, 21 patients (91%) were able to return to play and remain asymptomatic (12).
A valgus force is generated during the late cocking and early acceleration phases of throwing. This valgus force results in traction on the medial elbow structures, compression to the lateral side of the joint, and impingement posteriorly (10). Repetitive microtrauma can become pathologic when the elbow’s static and dynamic stabilizers are overwhelmed by physiologic demand. Several injuries are characteristically seen and collectively referred to as Little Leaguer’s elbow.
Medial epicondylar apophysitis (classic Little Leaguer’s elbow)
Little Leaguer’s elbow is a generic diagnosis often used in reference to medial epicondylar apophysitis. The apophysitis occurs from traction of the flexor-pronator musculature at the apophyseal insertion. The flexor-pronator musculature works to stabilize the elbow against the valgus force generated during late cocking. The medial epicondylar apophysis is the last elbow physis to close, usually 14 years of age in females and 17 years in males (9). As the apophysis is the weakest elbow structure in children, it is the site most vulnerable to injury in the developing elbow.
Affected athletes are usually 10 years of age or younger and present with progressive medial elbow pain, focal tenderness, and eventually decreased throwing distance and velocity. Pain usually occurs during the late cocking and early acceleration phase, which correlates with the highest valgus loads of the throwing cycle. Physical examination may reveal swelling over the medial epicondyle and tenderness to direct palpation. Upon elbow extension, a flexion contracture may be present. Patients do not typically exhibit valgus instability. AP and lateral radiographs should be obtained with comparison contralateral views. Radiographs may demonstrate widening or fragmentation of the medial epicondyle apophysis. Similar findings, however, have been noted in asymptomatic patients and may suggest an adaptive response to throwing. Relative rest from throwing and exacerbating activities is the mainstay of treatment, with ice and analgesics used for symptomatic management. Core and lower extremity strengthening is encouraged. After a 4- to 6-wk relative rest period, the athlete is progressed back to throwing if symptom free, with a 6-wk reintegration program as part of physical therapy, and focus is placed on future prevention and correct pitching mechanics (39).
As the patient approaches skeletal maturity and the medial epicondyle physis closes, the physis itself becomes less vulnerable to valgus stress (24). Both static and dynamic elbow stabilizers attach to the medial epicondyle. Typically, a discrete event (such as a throw home from outfield) overwhelms the closing physis in an older adolescent and can lead to an avulsion fracture. Workup and examination findings are similar to apophysitis; however, swelling is more commonly seen with fracture as opposed to apophysitis. In the general pediatric population, medial epicondyle fractures are often managed nonoperatively with cast immobilization. Indications for surgical referral for open reduction and internal fixation include intraarticular fragmentation, ulnar nerve involvement, open fracture, gross instability, and significant displacement. Despite lack of literature consensus, most fractures with <5 mm of displacement are treated nonoperatively (17).
However, in the throwing athlete, the threshold for fixation may be significantly lower owing to fear of instability affecting overhead motion. Outcomes for both operative and nonoperative treatment of avulsion fracture have been favorable. Lawrence et al. (33) examined a cohort of 20 adolescent athletes with medial epicondyle avulsion, wherein six were treated nonoperatively and 14 were treated surgically. Those undergoing surgery had an average displacement of 7 mm. All patients developed union after treatment and reported excellent satisfaction. All players, regardless of surgical or nonsurgical management, returned to a competitive level of sports participation. Half of those players managed surgically developed slight positional numbness postoperatively.
Whereas medial elbow injuries in throwers result from repetitive traction, lateral elbow injuries result from repetitive compression. Osteochondritis dissecans (OCD) is a localized area of avascular aseptic bone and, when present in the elbow, tends to occur on the anterolateral aspect of the capitellum. Subchondral collapse and loose body formation may ensue. Theories about the cause of OCD include simple repetitive mechanical trauma, disruption to the blood supply of a small area of subchondral bone, or disruption of endochondral ossification (19). Whereas OCD of the capitellum is typically seen in those over 10 years old, the younger child may develop the Panner disease. This self-limiting condition is characterized by fragmentation of the entire ossification center of the capitellum without the formation of loose bodies. Typically, there are no long-term sequelae, as opposed to OCD where the prognosis to return to high-level sports after surgical treatment is guarded (26). There is some argument that these conditions represent a disease continuum, given that in both, males are most commonly affected, the affected site and likely mechanisms similar, and earlier diagnosis facilitates full recovery; however, key differences include the presenting age, lesion morphology, and, most importantly, disease course (49). An older adolescent with a discrete chondral lesion on imaging warrants closer monitoring with a low threshold to refer to surgery.
Both OCD and the Panner disease typically present with insidious onset lateral elbow pain worse with throwing or axial loading (e.g., handstands in gymnastics). Physical examination commonly reveals an elbow effusion with loss of elbow extension and limitation of pronation and supination. Mechanical symptoms may suggest lesion instability or loose bodies and thus are more commonly seen in OCD. Radiographs of the elbow may show irregular calcification of the capitellum, while magnetic resonance imaging provides more sensitivity and allows visualization of the integrity of the chondral surface. Unstable OCD lesions, defined as violation of the chondral surface, may break off and form loose bodies. Unstable lesions and patients with mechanical symptoms may warrant surgical referral. The Panner disease and stable OCD lesions are initially treated conservatively with relative rest and graduated return to activity over the course of several months. Long-term studies suggest that the natural history of elbow OCD is not benign. Bauer et al. (8) reported that in 31 patients with OCD at a mean follow-up of 23 years, 50% had elbow symptoms and radiographic osteoarthritis was present in more than half of these patients. Data on long-term outcomes for surgical treatment of elbow OCD are limited. In a series of seven competitive female gymnasts with advanced OCD treated surgically, only one was able to return to high-level gymnastics (28). In a retrospective cohort study (11), arthroscopic surgery was performed on 10 baseball players (average age, 13.8 years) who failed conservative care. Prior to surgery, the average symptom duration was 9 months. Upon follow-up at an average of 3.9 years, only four returned to organized baseball out of eight who tried to continue playing.
Prevention of overuse throwing injuries revolves around limiting use and mitigating the risk factors discussed previously. Proper throwing mechanics should always be stressed and from as early an age as possible. Parents, coaches, and athletes should remain vigilant for signs of fatigue including decreased velocity, accuracy, or increased time between pitches. Two to three successive months of rest (four months is most preferable) from all overhead throwing should occur each year. The athlete should avoid pitching on multiple teams with overlapping seasons (20). Interestingly, a survey of 30 major league and 71 minor league pitchers conducted by Dr. Joseph Chandler suggests that earlier sport specialization may not be a necessity to pitch at a professional level. The pitchers recalled that high pitch counts (more than 75 per game) and reports of arm injuries were rare in their youth. The average age these professionals started pitching was 10.1 years, and major leaguers averaged later starts to throwing breaking pitches than minor leaguers.
Developing pitchers should focus on proper pitch placement and selection and situational awareness (i.e., throwing low with runners on base to force double plays) rather than trying to throw the fastest fastball. Pitch count guidelines should be followed. This starts with better awareness and education of these guidelines.
The trend of increasing adolescent throwing injuries has hopefully plateaued. This may be due to increased awareness and better adherence to pitch guidelines. However, single-sport specialization and the drive to throw faster march on. Teamwork, social interaction, and the handling of competition are a few of the skills learned on the baseball diamond that an adolescent continues to hone beyond an athletic career. We must remain vigilant to keep our youth healthy in one of our country’s pastimes, so they can reap the benefits of organized sports both within and beyond the playing field.
The authors declare no conflicts of interest and do not have any financial disclosures.
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