Overhead athletes, including baseball players, are subject to an increased risk of shoulder pain and injuries. Shoulder injuries such as rotator cuff tendonitis, tendonosis, bursitis, tears, impingement, and superior labrum anterior posterior (SLAP) lesions are commonly seen in this population.2 These injuries can account for over 90% of shoulder injuries observed in professional baseball pitchers.21
Baseball is a sport that involves repetitive overhead throwing during both competition and practice. As result, shoulder pain and injury are a common complaint among baseball players. Surveillance data have demonstrated that among high school sports from 2005 to 2007, baseball has the third highest shoulder injury rate, following football and wrestling;13 however, the underlying mechanism of shoulder injury among these sports can be very different. Approximately 44% of shoulder injuries in baseball were non-contact, the highest percentage among the sports.14 From 2005 to 2008, 43% of high school shoulder injuries in baseball were non-contact.20 Sprains and strains accounted for 55% of shoulder injuries in baseball, second only to volleyball. Of the shoulder injuries reported in baseball, 24% and 33% resulted from throwing and pitching, respectively. Others have reported that the shoulder is the most frequent site of injury in high school baseball, accounting for 18% of the total baseball injuries.14
Similar results were observed in higher levels of competition as well. From 1992 to 2004, non-contact injuries accounted for 42% and 64% of all competition and practice injuries in
National Collegiate Athletic Association (NCAA) baseball.15 Throwing and pitching accounted for 5% and 15% of all NCAA baseball injuries, respectively, and the shoulder was the most common injury site during competition (23%) and practice (16%). Two prospective studies of collegiate baseball players demonstrated that the shoulder was the first and second most frequent injury site, accounting for 24% and 13% of total injuries, respectively.16,17 In minor league baseball, the shoulder was the most commonly injured site, with 24% of all injuries occurring at the shoulder.18 Finally, in Major League baseball, injury of the shoulder caused the most disabled list days, at 28% of total, from 1989 to 1999.19 In a 5-year prospective study that followed 144 professional pitchers, 59% of the recorded injuries occurred at the shoulder.21
Whether in baseball competition or practice, pitchers perform the greatest amount of maximum effort throwing, usually while pitching. Catchers perform the greatest amount of moderate effort throwing, typically when passing the ball back to pitchers, and some maximum effort throwing to pick off a runner. On average, catchers make 4.4 to 6.5 pick-off throws per game at an average 90 to 97% of maximum effort, with mean throwing distance approximately 31 meters.94 Outfielders and infielders make fewer throws than pitchers and catchers, with outfielders performing more maximum effort throwing than infielders. The mean throwing distance of shortstops was about 24 meters, while the mean throwing distance of centerfielders ranged from 27 to 48 meters depending on competition levels.94 Among different positions in high school baseball, Collins and Comstock14 reported that injuries at shoulder were the most common in pitchers (34%), followed by catchers (25%), outfielders (24%), and infielders (7%). Similarly, Krajnik et al.20 found that 38% of shoulder injuries in high school baseball occurred in pitchers, followed by outfielders (26%), infielders (18%), and catchers (9%). Pitchers represented 48% of disabled list reports and 56% disabled list days in Major League Baseball.19
Such patterns indicated that the risk of shoulder injuries in baseball is associated with both intensity and volume of throwing.
Epidemiological evidence further supports the influence of throwing intensity in baseball pitchers. Adolescent pitchers with a fastball more than 85mph were at significantly higher risk of undergoing shoulder or elbow surgery.22 A prospective cohort study showed a significant association between pitch velocity and elbow injury in professional baseball.95 Furthermore, the three pitchers with the highest pitch velocity in the injured group required surgical intervention, while non-operative rehabilitation was assigned to others. Although it is plausible to assume the existence of significant relationship between throwing intensity and shoulder injury, the exact relationship remains unclear.
Epidemiological evidence also supports that the volume of throwing can contribute to increased risk of shoulder pain and injury. In a prospective cohort study, increased risk of shoulder pain was associated with increased pitch count per game and per season in youth baseball pitchers.23 In a case-control study, increased number of warm-up pitches, pitching appearance per year, innings pitched per year, pitches per game, pitches per year, and months per year of pitching were identified as risk factors for undergoing shoulder surgery in adolescent baseball pitchers.22
Pitching while fatigued or in pain were also identified as risk factors of shoulder surgery in adolescent baseball pitchers.22 Between 1999 and 2003, 73% of Major League baseball players placed on the disabled list had injuries classified as “wear and tear” or as caused by “overuse” or “insufficient rest”.24 Sports medicine experts generally agree that although baseball throwing is a very intense task, a single bout of throwing typically does not cause shoulder injury.26 While a baseball player may be able to identify a single throwing event which
precipitates the injury, it is the microtrauma accumulated with repetitive throwing over months or years that results in clinical structural damage.25,26 Complaints of simple shoulder pain, common in youth baseball, can be an early indicator of the development of an overuse injury.23