In-Game Workload Demands of Position Players in Major League Baseball.

BACKGROUND: Athletes who are well prepared for the physical demands of competition are less susceptible to injury. Defining and then preparing athletes for these in-game demands is critical to athlete health and performance. The injury burden within Major League Baseball (MLB) is significant and differs by position. Despite its importance, the workload demands have not been described for position players in MLB. HYPOTHESIS: That running demands would be significantly higher for outfielders, followed by infielders, and catchers, respectively, while batting and baserunning metrics would be similar across positions. STUDY DESIGN: Cohort study. LEVEL OF EVIDENCE: Level 3. METHODS: Total and high-speed running distance (>75% Vmax), high-speed running count, hard accelerations (>2.78 m/s/s), defensive and baserunning minutes, total and hard throws (>75% max), and bat swing counts were calculated from Statcast data. Players with 100 games or more in the 2018 season (n = 126) were included for analysis. RESULTS: All offensive and baserunning metrics were similar across positions; however, significant positional differences were observed for defensive and overall workload metrics. High-speed running was highest among outfielders (F1,7 = 27.1, P < 0.01), followed by infielders, then catchers. Hard accelerations (F1,7 = 12.9, P < 0.01) were highest among first basemen, then outfielders, remaining infielders, and catchers. Total throws (F1,7 = 17.7, P < 0.01) were highest among middle infielders. Hard throws (P < 0.01) were highest among shortstops and third basemen. CONCLUSION: In-game workloads differ significantly by defensive position in MLB. These differences in running, throwing, and hitting volumes have significant implications for physical preparation and injury return-to-play progressions to optimize performance and minimize injury and reinjury risk for these athletes. CLINICAL RELEVANCE: These data provide insight into how best to prepare athletes of different positions for the demands of the game both in terms of preseason preparation as well as return-to-play benchmarks following injury. These data should also serve as a platform for future research into the relationship between workload and injury among professional baseball players.

Differences in Glenohumeral Range of Motion and Humeral Torsion Between Right-Handed and Left-Handed Professional Baseball Pitchers.

BACKGROUND: Elite pitchers have demonstrated significant differences in glenohumeral range of motion and humeral torsion compared with the nonthrowing population. Furthermore, abnormal shoulder range of motion measurements have been associated with different injury risks and challenges in assessing rehabilitation progress. Variations in range of motion and torsion due to handedness in the asymptomatic professional population have yet to be investigated in the literature. HYPOTHESIS: No significant differences in glenohumeral range of motion and humeral torsion would exist between asymptomatic right- and left-handed professional pitchers. STUDY DESIGN: Cross-sectional study; Level of evidence, 3. METHODS: 217 Major League Baseball pitchers from a single organization were evaluated over a 7-year period between 2013 and 2020. Range of motion was measured with a standard goniometer. Ultrasound scanning was used to determine neutral position of the shoulder, and the degree of humeral torsion was measured with a goniometer. RESULTS: Right-handed pitchers demonstrated significantly greater values of glenohumeral external rotation (118.5° vs 112.7°; P < .001) in their throwing arms compared with their left-handed counterparts. Right-handed pitchers also showed greater values of glenohumeral internal rotation deficit (13.9° vs 4.8°; P < .001) and side-to-side differences in humeral retrotorsion (-23.1° vs -2.2°; P < .001). Left-handed pitchers demonstrated significantly greater flexion deficits in the throwing arm compared with their right-handed counterparts (7.5° vs 0.0°; P < .001). CONCLUSION: In the throwing arm, right-handed pitchers demonstrated significantly greater measures of external rotation, glenohumeral internal rotation deficit, and humeral retrotorsion compared with left-handed counterparts. Furthermore, right-handed pitchers demonstrated a significant side-to-side difference in retrotorsion, whereas left-handed pitchers did not. However, left-handed pitchers demonstrated a side-to-side shoulder flexion deficit that was not present in the cohort of right-handed pitchers. The correlation between humeral retrotorsion and increased external rotation indicates that osseous adaptations may play a role in range of motion differences associated with handedness. Additionally, these findings may explain observed differences in several throwing metrics between right- and left-handed pitchers. Knowledge of these differences can inform rehabilitation programs and shoulder maintenance regimens.

Pectoralis muscle injuries in Major and Minor League Baseball.

BACKGROUND AND HYPOTHESIS: Although shoulder and elbow injuries in professional baseball players have been thoroughly studied, little is known about the frequency and impact of pectoralis muscle injuries in this population. The purpose of this study was to use the official league injury surveillance system to describe pectoralis muscle injuries in professional baseball players in Major League Baseball (MLB) and Minor League Baseball (MiLB). Specifically, (1) player demographic characteristics, (2) return to play (RTP), (3) injury mechanism, (4) throwing- and batting-side dominance, and (5) injury rate per athlete exposure (AE) were characterized to guide future injury prevention strategies. METHODS: The MLB Health and Injury Tracking System database was used to compile all pectoralis muscle injuries in MLB and MiLB athletes in the 2011-2017 seasons. Injury-related data including diagnosis (tear or rupture vs. strain), player demographic characteristics, injury timing, need for surgical intervention, RTP, and mechanism of injury were recorded. Subanalyses of throwing- and batting-side dominance, as well as MLB vs. MiLB injury frequency, were performed. RESULTS: A total of 138 pectoralis muscle injuries (32 MLB and 106 MiLB injuries) were reported in the study period (5 tears or ruptures and 133 strains), with 5 of these being recurrent injuries. Operative intervention was performed in 4 athletes (2.9%). Of the 138 injuries, 116 (84.1%) resulted in missed days of play, with a mean time to RTP of 19.5 days. Starting pitchers sustained the greatest proportion of pectoralis injuries (48.1%), with pitching being the most common activity at the time of injury (45.9%). A majority of injuries (86.5%) were sustained during non-contact play. Overall, 87.5% of injuries occurred on the player's dominant throwing side and 81.3% occurred on the player's dominant batting side. There was no significant difference in the rate of pectoralis injuries in the MLB regular season (0.584 per 10,000 AEs) vs. the MiLB regular season (0.425 per 10,000 AEs) (P = .1018). CONCLUSION: Pectoralis muscle injuries are most frequently non-contact injuries, most commonly sustained by pitchers. An understanding of these injuries can guide athletic trainers and management in expectation management and decision making, in addition to directing future efforts at injury prevention.

Chronic adaptations of the long head of the biceps tendon and groove in professional baseball pitchers.

BACKGROUND AND HYPOTHESIS: The long head of the biceps tendon (LHBT) plays a significant shoulder stabilizing role during pitching, with the large forces and repetitions involved in overhead throwing likely contributing to LHBT pathology. Determining whether the LHBT undergoes adaptive changes in baseball pitchers and how these changes relate to bicipital groove morphology can improve our understanding of the biceps function at the glenohumeral joint. Therefore, the purpose of this study was to determine the chronic adaptations of the bicipital groove morphology and the LHBT in professional baseball pitchers, with a secondary purpose of evaluating biceps integrity as it relates to torsional changes of the bicipital groove. We hypothesized that the throwing arm of professional baseball pitchers would exhibit chronic adaptations of the LHBT compared with their nonthrowing arm, and that these adaptations would be related to the bicipital groove morphology. MATERIALS AND METHODS: Fifty-three professional baseball pitchers were enrolled at the beginning of the 2015 Major League Baseball spring training. Ultrasound was used to bilaterally measure humeral retroversion and to capture images of the bicipital groove and the LHBT. MATLAB software was used to calculate the area of the bicipital groove, and ImageJ software was used to quantify the area, echogenicity, and circularity of the LHBT. RESULTS: The dominant arm LHBT cross-sectional area was significantly smaller than the nondominant arm (9 mm2 vs. 10 mm2; P = .011), whereas the dominant arm LHBT echogenicity was significantly higher than the nondominant arm (65 optical density vs. 59 optical density; P = .002). Pitchers with more bicipital groove rotational adaptation (more retroversion) had significantly more LHBT echogenicity adaptation compared with pitchers with less bicipital groove rotational adaptation (12 vs. 2; P = .023). CONCLUSION: There are significant bilateral differences in the LHBT of professional baseball pitchers. An adaptation in bony rotation was associated with a larger bilateral difference in LHBT echogenicity but was not related to bilateral differences in LHBT area or circularity. Therefore, the bilateral difference in echogenicity is impacted by bony morphology, whereas the bilateral difference in cross-sectional area may be independent of bony morphology in this healthy population.

Epidemiology of acromioclavicular joint injuries in professional baseball: analysis from the Major League Baseball Health and Injury Tracking System.

BACKGROUND: Shoulder injuries account for a large portion of all recorded injuries in professional baseball. Much is known about other shoulder pathologies in the overhead athlete, but the incidence and impact of acromioclavicular (AC) joint injuries in this population are unknown. We examined the epidemiology of AC joint injuries in Major League Baseball (MLB) and Minor League Baseball (MiLB) players and determined the impact on time missed. METHODS: The MLB Health and Injury Tracking System was used to compile records of all MLB and MiLB players from 2011 to 2017 with documented AC joint injuries. These injuries were classified as acute (sprain or separation) or chronic (AC joint arthritis or distal clavicular osteolysis), and associated data extracted included laterality, date of injury, player position, activity, mechanism of injury, length of return to play, and need for surgical intervention. RESULTS: A total of 312 AC joint injuries (183 in MiLB players and 129 in MLB players; range, 39-60 per year) were recorded: 201 acute (64.4%) and 111 chronic (35.6%). A total of 81% of acute and 59% of chronic injuries resulted in time missed, with a mean length of return to play of 21 days for both. Of the injuries in outfielders, 79.6% were acute (P < .0001), as were 66.3% of injuries in infielders (P = .004). Pitchers and catchers had more equal proportions of acute and chronic AC injuries (P > .05 for all). Acute AC injuries occurred most often while fielding (n = 100, 84.7%), running (n = 25, 80.6%), and hitting (n = 19, 61.3%), whereas chronic injuries tended to be more common while pitching (n = 26, 68.4%). Of contact injuries, 82.5% were acute (P < .0001), whereas 59.0% of noncontact injuries were chronic (P = .047). MLB players showed consistently higher regular-season rates of both acute and chronic AC injuries than MiLB players (P < .0001 for each). CONCLUSION: Acute AC joint injuries are contact injuries occurring most commonly among infielders and outfielders while fielding that result in 3 weeks missed before return to play, whereas chronic AC joint injuries occur more commonly in pitchers and catchers from noncontact repetitive overhead activity. Knowledge of these data can better guide expectation management in this elite population to better elucidate the prevalence of 2 common injury patterns in the AC joint.

Preventing Concussions From Foul Tips and Backswings in Professional Baseball: Catchers' Perceptions of and Experiences With Conventional and Hockey-Style Masks.

OBJECTIVE: To understand catchers' preferences for mask type and perceptions regarding safety, comfort, and fit, and determine whether mask type is correlated with self-reported concussion and related symptoms after impacts from foul tips or backswings. DESIGN: Cross-sectional study. SETTING: Survey of active baseball catchers. PARTICIPANTS: Professional baseball catchers. INTERVENTION: From May 1, 2015, to June 30, 2015, an online survey was administered in English and Spanish to all Major and Minor League catchers (n = 836). MAIN OUTCOME MEASURES: Survey items addressed the type of mask routinely and previously used (conventional or hockey style); brand and material (steel or titanium); perceptions regarding safety, comfort, and fit; and experiences with concussions. RESULTS: The sample consisted of 596 catchers of which 26% reported being diagnosed with a concussion. Some concussions occurred from non-baseball activities, such as car accidents or off the field incidents. For those that occurred playing baseball, 35% resulted from a foul tip. Once catchers entered professional baseball, the use of a conventional mask rose significantly: 71% of catchers reported wearing conventional-style masks, and 30% hockey-style masks at the time the survey was conducted (P < 0.05). Both conventional and hockey-style mask wearers significantly selected hockey-style masks as providing better overall safety and protection than conventional masks (P < 0.05). CONCLUSIONS: This research supports foul tips as an important cause of concussion in catchers and provides important information about preferences among catchers for masks that are not perceived as the safest and strongest. Future research should supplement these data by conducting laboratory testing to determine which masks are stronger and by collecting qualitative data to explore why some players are more likely to wear a mask type that they perceive as offering less safety or protection.

Management of common upper extremity injuries in throwing athletes: a critical review of current outcomes.

Given the rising incidence and prevalence of shoulder injuries in throwing athletes, this review aims to evaluate management options and outcomes of common shoulder injuries in overhead throwers. Laxity of the glenohumeral joint is often adaptive for overhead athletes to achieve the velocity necessary to compete in the professional ranks. Surgical repair of the stabilizers of the humeral head-specifically the labrum and rotator cuff-often causes inflammation, scarring, and overtensioning of the glenohumeral joint which lead to poor postoperative performance. Thus, nonsurgical management should be exhausted in this population before considering surgical intervention.

Epidemiology and Impact of Prior Musculoskeletal Injury and Orthopaedic Surgery on Draft Rank, Availability, and Short-term Performance in Major League Baseball: A Summary Analysis and Matched Cohort of 1890 Predraft Players.

BACKGROUND: Despite the many reports of injury rates in Major League Baseball (MLB), little is known about the epidemiology or impact of prior musculoskeletal injuries and surgical procedures among players entering the MLB draft. PURPOSE: To determine the (1) epidemiology of all musculoskeletal injuries and surgical procedures among players entering the MLB draft, (2) impact of injury or surgery on draft rank, (3) impact of injury or surgery on availability within the first 2 years of play in the MLB, and (4) impact of injury or surgery on performance. STUDY DESIGN: Cohort study; Level of evidence, 3. METHODS: We retrospectively reviewed 1890 medical records that were completed by MLB team physicians as preparticipation physical assessment prior to the draft from 2014 to 2018. Players were divided into 3 groups: noninjured, nonoperative, and operative. Draft status, overall draft rank, missed games, batting average, and earned run average for the first 2 seasons of MLB play were obtained for all available players. Players across all 3 groups were compared with linear, logistic, and beta regression models, controlling for age, position, injury status, and draft rank. Unadjusted differences among groups were assessed with 1-way analysis of variance. RESULTS: Overall, 750 position players and 1140 pitchers were included, of whom 22.8% had no reported injury history; 48.8% reported injury treated nonoperatively; and 28.5% were treated operatively. The most common predraft injuries were elbow tendinitis (n = 312), ulnar collateral ligament injury (n = 212), and shoulder labral tear (n = 76). The most common predraft treatments were physical therapy (n = 922), ulnar collateral ligament reconstruction (n = 115), and fracture fixation (n = 69). Of the 1890 players, 719 were drafted and played for at least 2 years. No difference was found among noninjured, nonoperative, and operative groups in terms of draft rank, games missed, or performance. Players with a nonoperative injury had a decreased odds ratio of being drafted (0.738; P = .017). CONCLUSION: More than half of the players entering the MLB reported a history of musculoskeletal injury requiring treatment, and the most commonly affected joints were the shoulder and elbow. Musculoskeletal history did not affect draft rank, short-term availability, or performance for MLB prospects.

Effects of Ulnar Collateral Ligament Reconstruction on Pitch Selection in Major League Baseball Pitchers.

BACKGROUND: Ulnar collateral ligament (UCL) injuries represent one of the most common impairments to the throwing arm of professional pitchers. Return to play and postoperative performance metrics have been studied extensively, but pitch selection before and after surgery has not been evaluated. PURPOSE/HYPOTHESIS: This study aimed to characterize the effects of UCL reconstruction on pitch selection in Major League Baseball (MLB) pitchers. We hypothesized that pitchers will throw fewer fastballs and a greater percentage of off-speed pitches after undergoing UCL reconstruction. STUDY DESIGN: Retrospective cohort study; Level of evidence, 3. METHODS: Using publicly available data, we evaluated MLB pitchers who underwent UCL reconstruction between 2003 and 2014. Pitching data were collected for the 2 seasons before UCL reconstruction as well as the first 2 seasons after reconstruction; the data consisted of the total number of pitches thrown and the percentage of fastballs, curveballs, changeups, and sliders. Repeated-measures analysis of variance was used with post hoc least significant difference pairwise t tests to evaluate for statistical significance at P < .05. RESULTS: Overall, 87 pitchers (mean age, 28.2 ± 3.5 years) met all inclusion and exclusion criteria. There was a statistically significant difference in the total number of pitches thrown before and after surgery (P < .01) as well as in the percentage of fastballs thrown before and after surgery (P = .02). There was also a statistically significant increase in the use of curveballs between 1 and 2 years postoperatively (7.5% and 8.8%, respectively; P = .01). No other findings were statistically significant. CONCLUSION: Pitchers who underwent UCL reconstruction were shown to have a statistically significant decline in the percentage of fastballs thrown postoperatively as compared with before injury, with a compensatory trend toward an increased use of curveballs and sliders.

Fat Fracture: A Rare Cause of Anterior and Medial Knee Pain in a Professional Baseball Player.

Blunt trauma to the anterior knee typically results in a contusion or fracture of the patella. Additionally, injury to the extensor mechanism may come from a partial or full disruption of the patellar or quadriceps tendon. A professional baseball player suffered an injury to his knee after he collided with an outfield wall. Acute swelling in the suprapatellar soft tissues concealed a palpable defect, which initially was suspected to be an injury to the quadriceps tendon. Magnetic resonance imaging of the knee revealed an intact extensor mechanism; moreover, a fracture of the subcutaneous fat anterior to the quadriceps tendon was evident and diagnosed as a fat fracture. Fat fracture is a rare diagnosis, and to the best of our knowledge, this is the first reported diagnosis in a professional athlete. Conservative management including, but not limited to, range of motion exercises, hydrotherapy, and iontophoresis effectively treated the athlete's injury.

The Thrower's Shoulder.

Overhead athletes subject their shoulders to extreme repetitive torque, compression, distraction, and translation stresses, resulting in adaptive changes of the soft tissues and osseous structures within and around the glenohumeral joint. These anatomic adaptations result in biomechanical enhancements, which improve performance. Understanding the difference between necessary and adaptive changes and pathologic findings is critical when making treatment decisions. Injuries to the shoulder of the overhead athlete can be generally classified into three groups: internal impingement, internal impingement with acquired secondary anterior instability, and primary anterior or multidirectional instability. Although advances in surgical techniques have allowed surgeons to address the pathology in these groups, merely attempting to restore the shoulder to so-called normal can adversely alter adaptive changes that allow high levels of performance.

Magnetic Resonance Imaging Predictors of Failure in the Nonoperative Management of Ulnar Collateral Ligament Injuries in Professional Baseball Pitchers.

BACKGROUND: A medial ulnar collateral ligament (UCL) injury of the elbow is an increasingly common injury in professional baseball pitchers. Predictors of success and failure are not well defined for the nonoperative management of these injuries. PURPOSE: To evaluate the efficacy of objective measures to predict failure of the nonoperative management of UCL injuries. STUDY DESIGN: Case-control study; Level of evidence, 3. METHODS: Thirty-two professional pitchers (82%) met inclusion criteria and underwent an initial trial of nonoperative treatment for UCL tears based on clinical and radiological findings. Age, preseason physical examination results, magnetic resonance imaging (MRI) characteristics, and performance metrics were analyzed for these pitchers. Successful nonoperative management was defined as a return to the same level of play or higher for >1 year. Failure was defined as recurrent pain or weakness requiring a surgical intervention after a minimum of 3 months' rest when attempting a return to a throwing rehabilitation program. RESULTS: Thirty-two pitchers (mean age, 22.3 years) who underwent initial nonoperative treatment of UCL injuries were evaluated. Thirty-four percent (11/32) failed and required subsequent ligament reconstruction. Sixty-six percent (21/32) successfully returned to the same level of play for 1 year without a surgical intervention. There was no significant difference seen in physical examination findings or performance metrics between these patients. When comparing MRI findings between the groups, 82% (9/11) ( P < .001) who failed nonoperative management had distal tears, and 81% (17/21) who did not fail had proximal tears ( P < .001). When adjusting for age, location, and evidence of chronic changes on MRI, the likelihood of failing nonoperative management was 12.40 times greater ( P = .020) with a distal tear. No other variable alone or in combination reached significance. When combining the parameters of a high-grade tear and distal location, 88% (7/8) failed nonoperative management. CONCLUSION: In professional pitchers, distal UCL tears showed significantly higher odds of failure with nonoperative management compared with proximal tears. Thus, tear location should be considered when deciding between operative and nonoperative management.

Throwing-related injuries of the subscapularis in professional baseball players.

OBJECTIVE: To describe the MR appearance of a series of throwing-related injuries to the subscapularis muscle-tendon complex among baseball players. MATERIALS AND METHODS: A retrospective review of MR scans of the shoulder in players from 1 professional baseball organization over the course of 5 years was performed to identify cases with findings suggestive of subscapularis injury. These findings were graded and the medical record was reviewed to assess clinical findings, treatment, and follow-up. Preinjury baseline measurements of arm external rotation at 90° of abduction were compared to measurements from a noninjured cohort to evaluate whether this measure is a risk factor for injury. RESULTS: A total of 133 MR scans of the shoulder were evaluated. Eleven of the scans demonstrated signal changes suggesting subscapularis injury; 10 of these 11 patients had clinical findings supporting a diagnosis of throwing-related subscapularis strain. There were four grade 1, four grade 2, and two grade 3 injuries. All injuries occurred in the inferior half of the subscapularis at the myotendinous junction. Risk of subscapularis injury increased with lower levels of dominant arm external rotation (odds ratio, 1.12; 95% CI, 1.07-1.21; p < 0.001). A threshold of dominant arm external rotation of <106° demonstrated sensitivity of 0.700 (95% CI, 0.392-0.897) and specificity of 0.951 (95% CI, 0.888-0.982) for subscapularis injury. CONCLUSION: Throwing-related subscapularis injuries occur in the inferior half of the muscle at the myotendinous junction. Our data suggest that there is an increased risk of these injuries with lower levels of dominant arm external rotation.

The Relationship Between Glenohumeral Internal Rotational Deficits, Total Range of Motion, and Shoulder Strength in Professional Baseball Pitchers.

INTRODUCTION: Although the lack of internal rotation (IR) and total range of motion (TRM) has been identified as a significant contributing factor of shoulder injuries, our goal was to determine whether a relationship exists between glenohumeral internal rotational deficits (GIRD), TRM, and shoulder strength in professional baseball pitchers. Our hypothesis was that GIRD with TRM differences within 5° will not lead to decreased shoulder strength; however, a shoulder with >5° of TRM difference with GIRD will lead to decreased shoulder strength. METHODS: The study was conducted over a 4-year period and included 193 major and minor league pitchers. All measurements were taken prior to the pitcher's engaging in any baseball-related activities on the day of measurements. The entire measurement arc of passive range of motion (PROM), including external rotation (ER) and IR, was defined as the TRM. GIRD was defined as a loss of 25° or more of IR of the throwing shoulder compared with the nonthrowing shoulder. Shoulder strength measurements were obtained using a validated digital dynamometer with the arm in 90° of abduction and with the arm in 110° of flexion and 30° of abduction measured in pounds. RESULTS: The IR deficit was 5.89° (SD = 9.24°) in non-GIRD pitchers and 25.52° (SD = 4.35°) in GIRD pitchers (P > 0.001). The ER change was 124.08° (SD = 11.21°) in non-GIRD pitchers and 127.79° (SD = 9.15°) in GIRD pitchers. The total arc of motion was 179.54° (SD = 14.53°) in non-GIRD pitchers and 171.93° (SD = 12.34°) in GIRD pitchers (P > 0.001). The strength in the shoulder, measured with the arm in 90° of abduction, was 29.61 lb (SD = 4.76 lb) in non-GIRD pitchers versus 28.65 lb (SD = 4.81 lb) in GIRD pitchers. The strength with the arm in 110° of flexion and 30° of abduction was 29.43 lb (SD = 5.01 lb) in non-GIRD pitchers versus 28.13 lb (SD = 4.76 lb) in pitchers with GIRD (P = 0.043). Deficiencies in total arc of motion (P < 0.001) and shoulder strength (P < 0.043) were significantly associated with GIRD. DISCUSSION: In our evaluation of 193 pitchers examined during their preseason physical examinations, we identified a statistically significant association between decreased total arc of motion, decreased shoulder strength, and GIRD.

Relationship between humeral torsion and injury in professional baseball pitchers.

BACKGROUND: High levels of humeral torsion allow baseball pitchers to achieve maximum external rotation in the late cocking phase of pitching with lower twisting and shear forces on the long head of the biceps tendon and rotator cuff tendons. HYPOTHESIS: Humeral torsion is inversely related to the incidence and severity of shoulder injuries and other upper extremity injuries in professional baseball pitchers. STUDY DESIGN: Case-control study; Level of evidence, 3. METHODS: A total of 25 professional pitchers from a single Major League Baseball organization were prospectively recruited into this study. Computed tomography (CT) was performed on dominant and nondominant humeri, and image data were processed with a 3-dimensional volume-rendering postprocessing program. The software program was then modified to model a simplified throwing motion and to measure potential internal impingement distances in a small subset of players. Players were followed for 2 years after CT, and the number of days missed from pitching activities was recorded as a measure of injury severity and incidence. RESULTS: The mean dominant humeral torsion was 38.5° ± 8.9°; the mean nondominant humeral torsion was 27.6° ± 8.0°. The difference between dominant and nondominant torsions was significant (P < .0001). Among the 11 pitchers (44%) injured during follow-up, 5 players had shoulder injuries, 7 had elbow injuries, and 2 had finger injuries. Dominant humeral torsion was a statistically significant predictor of severe injuries (≥30 days; P = .048) but not of milder injuries. Among injured players, higher numbers of days missed because of injury were strongly correlated with lower degrees of dominant humeral torsion (r = -0.78; P = .005) and smaller differences between dominant and nondominant humeral torsions (r = -0.59; P = .055). There was no significant association between the incidence of shoulder injury and minimum glenoid-tuberosity distance in the dominant or nondominant shoulder or degree of dominant glenoid version. CONCLUSION: A strong relationship was found between lower degrees of dominant humeral torsion and more severe upper extremity injuries as well as a trend relating lower side-to-side differences in torsion with more severe dominant upper extremity injuries. In addition, there was a higher incidence of severe injuries in players with lower degrees of dominant torsion. If future studies confirm these results, humeral torsion measurements could play a role in risk assessment in pitchers.