Some studies have evaluated anatomic variation among pitchers as a risk factor for injury. Polster and colleagues20 performed computed tomography (CT) scans with 3-dimensional reconstructions on the humeri of both the throwing and non-throwing arms of 25 MLB pitchers to determine if humeral torsion was related to the incidence and severity of upper extremity injuries in these athletes. The authors defined a severe injury as those which kept the player out for >30 days. Overall, 11 pitchers were injured during the 2-year study period. There was a strong inverse relationship between torsion and injury severity such that lower degrees of dominant humeral torsion correlated with higher injury severity (P = .005). However, neither throwing arm humeral torsion nor the difference in torsion between throwing and non-throwing humeri were predictive of overall injury incidence. While this is a nonmodifiable risk factor, it is important to understand how the pitcher’s anatomy plays a role in risk of injury.20 Understanding nonmodifiable risk factors may be helpful in the future to risk stratify, prognosticate, and modulate modifiable risk factors such as cumulative work.
Elbow
Injuries to the elbow have become more common in recent years amongst MLB players, although the literature regarding risk factors for elbow injuries is sparse.4,6 Wilk and colleagues21 performed a prospective study to determine if deficits in glenohumeral passive range of motion (ROM) increased the risk of elbow injury in MLB pitchers. Between 2005-2012, the authors measured passive shoulder ROM of both the throwing and non-throwing shoulder of 296 major and minor league pitchers and followed them for a median of 53.4 months. In total, 38 players suffered 49 elbow injuries and required 8 surgeries, accounting for a total of 2551 days spent on the disabled list (DL). GIRD and external rotation insufficiency were not correlated with elbow injuries. However, pitchers with deficits of >5° in total rotation between the throwing and non-throwing shoulders had a 2.6 times greater risk for injury (P = .007) and pitchers with deficits of ≥5° in flexion of the throwing shoulder compared to the non-throwing shoulder had a 2.8 times greater risk for injury (P = .008).21 Prior studies have demonstrated trends towards increased elbow injury in professional baseball pitchers with an increase in both elbow valgus torque as well as shoulder external rotation torque; maximum pitch velocity was also shown to be an independent risk factor for elbow injury in professional baseball pitchers.10,11 These injuries typically occur during the late cocking/early acceleration phase of the pitching cycle, when the shoulder and elbow experience the most significant force of any point in time during a pitch (Figure 2).17 At our institution, there are several ongoing studies to determine the relative contributions of pitch velocity, number, and type to elbow injury rates. Prospective studies are also ongoing at other institutions.
Shoulder
Shoulder injuries are one of the most common injuries seen in MLB players, specifically pitchers. Similar to the prior study, Wilk and colleagues22 recently performed a prospective study to determine if passive ROM of the glenohumeral joint in MLB pitchers was predictive of shoulder injury or shoulder surgery. As in the previous study, the authors’ measured passive shoulder ROM of the throwing and non-throwing shoulder of 296 major and minor league pitchers during spring training between 2005-2012 and obtained an average follow-up of 48.4 months. The authors found a total of 75 shoulder injuries and 20 surgeries among 51 pitchers (17%) that resulted in 5570 days on the DL. While total rotation deficit, GIRD, and flexion deficit had no relation to shoulder injury or surgery, pitchers with <5° greater external rotation in the throwing shoulder compared to the non-throwing shoulder were more than 2 times more likely to be placed on the DL for a shoulder injury (P = .014) and were 4 times more likely to require shoulder surgery (P = .009).22 The authors concluded that an insufficient side-to-side difference in external rotation of the throwing shoulder increased a pitcher’s likelihood of shoulder injury as well as surgery.
Other
One area that has not received as much attention as repetitive use injuries of the shoulder and elbow is acute collision injuries. Collision injuries include concussions, hyperextension injuries to the knees, shoulder dislocations, fractures of the foot and ankle, and others.23 Catchers and base runners during scoring plays are at a high risk for collision injury. Recent evidence has shown that catchers average approximately 2.75 collision injuries per 1000 athletic exposures (AE), accounting for an average of 39.1 days on the DL per collision injury.23 However, despite these collision injuries, catchers spend more time on the DL from non-collision injuries (specifically shoulder injuries requiring surgical intervention), as studies have shown 19 different non-collision injuries that accounted for >100 days on the DL for catchers compared to no collision injuries that caused a catcher to be on the DL for >100 days.23 The position of catcher is not an independent risk factor for sustaining an injury in MLB players.5