Biomechanics of the shoulder in youth baseball pitchers: implications for the development of proximal humeral epiphysiolysis and humeral retrotorsion

The Immature Pediatric Appendicular Skeleton

Growth and maturation occur in a predictable pattern throughout the body and within each individual bone. In the appendicular skeleton, endochondral ossification predominates in long bones and growth plates. The ends of these long bones are sites of relative weakness in the immature skeleton and prone to injury from acute insult and overuse. We present the normal histoanatomy and physiology of the growth plate complex, highlighting the unique contribution of each component and shared similarities between primary and secondary complexes. Components of the growth plate complex include the physis proper, subjacent vascularity within the growth cartilage, and the ossification front. The second section describes imaging considerations and features of normal and abnormal growth. Finally, we review the Salter-Harris classification for acute fractures and offer examples of characteristic overuse injury patterns involving the epiphyseal (proximal humerus and distal radius), apophyseal (medial epicondyle and tibial tubercle), and secondary growth plate complexes (medial femoral condyle and capitellar osteochondritis dissecans). This article provides a foundation and basic framework to better understand and anticipate potential complications and growth disturbances and to ensure optimal follow-up and early intervention when treatment can be less invasive.

Kinematic Modeling of Pitch Velocity in High School and Professional Baseball Pitchers: Comparisons With the Literature

Background

Kinematic parameters predictive of pitch velocity have been evaluated in adolescent and collegiate baseball pitchers; however, they have not been established for high school or professional pitchers.

Purpose

To create multiregression models using anthropometric and kinematics features most predictive for pitch velocity in high school and professional pitchers and compare them with prior multiregression models evaluating other playing levels.

Study Design

Descriptive laboratory study.

Methods

High school (n = 59) and professional (n = 337) baseball pitchers threw 8 to 12 fastballs while being evaluated with 3-dimensional motion capture (480 Hz). Using anthropometric and kinematic variables, multiregression models for pitch velocity were created for each group. A systematic review was conducted to determine previous studies that established kinematic models for ball velocity in youth, high school, and collegiate pitchers.

Results

Leg length was predictive of pitch velocity for high school and professional pitchers (P < .001 for both). When compared with previously established models for pitch velocity, almost all groups were distinct from one another when assessing age (P maximum < .001), weight (P max = .0095), and pitch velocity (P max < .001). Stride length was a significant predictor for the youth/high school pitchers, as well as the current study's high school and professional pitchers (P < .001 for all). Maximal shoulder external rotation (collegiate: P = .001; professional: P < .001) and maximal elbow extension velocity (high school/collegiate: P = .024; collegiate: P < .001; professional: P = .006) were shared predictors for the collegiate and current study's professional group multiregression models. Trunk flexion at ball release was a commonly shared predictor in the youth/high school (P = .04), high school/collegiate (P = .003), collegiate (P < .001), and the current study's professional group (P < .001).

Conclusion

Youth, high school, collegiate, and professional pitchers had unique, predictive kinematic and anthropometric features predictive of pitch velocity. Leg length, stride length, trunk flexion at ball release, and maximal shoulder external rotation were predictive features that were shared between playing levels.

Clinical Relevance

Coaches, clinicians, scouts, and pitchers can consider both the unique and the shared predictive features at each playing level when attempting to maximize pitch velocity.

A narrative review of little league shoulder: proximal humeral physis widening is only one piece of the puzzle, it is time to consider posterior glenoid dysplasia

Baseball athletes across all levels of play are at an increased risk for upper extremity injury due to the supraphysiologic demands on the shoulder and elbow during overhead throwing. Little league baseball players present with a unique subset of injuries that can affect the growth plate, commonly at the shoulder or the elbow. Ascertaining a diagnosis and plan of care for little league shoulder (LLS) historically focuses on the proximal humeral physis in skeletally immature throwing athletes presenting with shoulder pain. However, while not a current standard of care, posterior glenoid dysplasia is often present in youth baseball athletes presenting with LLS, warranting a shift in the way clinicians evaluate for and treat the youth baseball athlete's pathologic shoulder. Therefore, purpose of this narrative review is 2-fold: first, to describe the current standard of care as it relates to a diagnosis of LLS, and second, to critically describe a comprehensive evaluation process for youth throwing athletes with shoulder pain that includes screening for evidence of posterior glenoid dysplasia. This paper summarizes the current state of the available evidence for anatomic considerations of LLS in the baseball athletes throwing shoulder. Additionally, we provide a framework for clinical evaluation using a multidisciplinary approach to evaluate the entire kinetic chain of the youth baseball athlete presenting with LLS and posterior glenoid dysplasia. A case study is presented to describe common presentations, clinical and objective examinations, and a plan of care from time of evaluation to return to throwing.

Humeral Torsion in Relation to Shoulder Range of Motion in Elite Field Hockey Players

CONTEXT

Sport-specific adaptations in shoulder rotation range of motion (ROM) and the relationship with humeral torsion have been described in overhead-throwing sports. However, information is lacking for other shoulder-loading sports such as field hockey. Therefore, this study's purpose was to evaluate humeral torsion in elite, male field hockey players and explore its association with shoulder ROM.

DESIGN

Cross-sectional study.

METHODS

Twenty-five male, elite field hockey players were included. Humeral torsion and shoulder external and internal rotation ROM were evaluated bilaterally by ultrasound and an inclinometer smartphone application, respectively.

RESULTS

Field hockey players showed a significantly increased humeral retroversion on the dominant compared with the nondominant side (P < .001; Cohen d = 1.75), along with a significantly increased external (P = .004; Cohen d = -0.64) and decreased internal rotation ROM (P = .003; Cohen d = 0.65). This finding illustrates a shift in total shoulder rotational ROM arc. Correlation analysis showed a significant moderate association between the increased humeral retroversion and decreased internal rotation ROM on the dominant side (r = .523).

CONCLUSIONS

Elite male field hockey athletes show sport-specific adaptations regarding humeral torsion and shoulder rotation ROM, similar to throwing athletes. These findings increase our insight into the field hockey athlete's shoulder, which is essential to optimize performance and assist in correctly interpreting shoulder rotational ROM measurements.

An Analysis of Intrapitch Variation in Joint and Segment Velocities With Throwing Arm Kinetics in High School and Professional Baseball Pitchers

BACKGROUND

Improper sequencing order of maximal joint and segment velocities has been identified as an important predictor for both throwing arm kinetics and ball velocity.

PURPOSE

To investigate the intrapitcher variation of maximal segment velocities and the relationship to throwing arm kinetics and ball velocity in high school (HS) and professional (PRO) pitchers.

STUDY DESIGN

Descriptive laboratory study.

METHODS

HS (n = 59) and PRO (n = 338) pitchers, instructed to throw 8 to 12 fastball pitches, were evaluated with 3-dimensional motion capture (480 Hz). Maximal joint and segment velocities were calculated for each pitch, and the standard deviation of the maxima was calculated per pitcher. These standard deviations were used to classify pitchers as "low variance" or "high variance" for each segmental velocity subgroup, "overall low variance" or "overall high variance" based on cumulative segment velocity variation, or "population," with any pitcher eligible to be included in multiple subcategories. Maximal velocities and throwing arm kinetics were compared among the various subgroups.

RESULTS

The HS low-variance shoulder internal rotation velocity subgroup (4949 ± 642 deg/s) had significantly lower maximal shoulder internal rotation velocity compared with HS population (5774 ± 1057 deg/s) (P < .001); similar findings were observed for PROs (5269 ± 835 vs 5824 ± 1076 deg/s; P < .001), as well as lower shoulder superior force compared with the PRO population (14.8% ± 8.8% vs 17.8% ± 8.8% body weight; P = .001). The PRO low-variance lead knee extension velocity subgroup had significantly lower maximal lead knee extension velocity (216 ± 135 vs 258 ± 125 deg/s; P = .001) and shoulder distractive force (111.5% ± 14.4% vs 115.6% ± 15.9% body weight; P = .003) compared with the PRO population. The PRO overall low-variance subgroup had significantly lower shoulder distractive force (111.8% ± 14.1% vs 119.6% ± 15.5% body weight; P = .008) and elbow anterior force (40.6% ± 5.0% vs 43.6% ± 6.2% body weight; P = .008) compared with the PRO overall high-variance subgroup.

CONCLUSION

HS and PRO pitchers with low variance for joint and segment velocities achieved significantly lower maximal velocities in the subgroup of interest, while preserving ball velocity. PRO pitchers with overall low variance among multiple maximal joint and segment velocities demonstrated decreased shoulder distractive and elbow anterior force.

CLINICAL RELEVANCE

PRO pitchers with low intrapitch variation in maximal joint and segment velocities may be viewed as kinetically conservative throwers. These pitchers with similarly maintained mechanics between pitches may have an increasingly regimented form that preserves kinetic forces about the throwing arm. The opposite may be true for PRO pitchers with increased variability in segmental velocities during their pitching motion, as they showed increased throwing arm kinetics including shoulder distractive and elbow anterior force compared with the overall low-variance group, theoretically increasing their risk of injury.

A Model for Causality of Pitching-related Overuse Injuries in Women's Fastpitch Softball

Fastpitch softball is a popular women's sport, and athletes, particularly pitchers, are at high risk for overuse injury. Softball-related injury rates are low; however, the prevalence of overuse injuries is high. Injuries at the high school and collegiate levels occur early in the season, and approximately 50% of shoulder and elbow injuries in softball are attributable to overuse. Survey research showed 77% of high school pitchers pitch with pain, and 73% of collegiate pitchers reported an overuse injury in the previous season. Modifiable and non-modifiable intrinsic and extrinsic risk factors contribute to injury risk in a model that can be used in history taking, clinical examination, and management of softball-related injuries. In this manuscript, we present a scoping review of fastpitch softball injury research by competitive levels from 1990 to present. We also introduce a model for overuse injury causality in this athlete population. With this information, clinicians will be able to identify risk factors related to injury in softball pitchers. More research is needed to make evidence-based recommendations for injury prevention in this athlete population.

Extracorporeal Shock Wave Therapy and the Handstand-Position Radiography for Proximal Humeral Epiphysiolysis in Elite Gymnasts: A Report of Two Cases

We report two cases of proximal humeral epiphysiolysis in elite gymnasts. Both patients presented with shoulder pain during weight-bearing movements. The patient in case 1, treated with extracorporeal shock wave therapy (ESWT), exhibited rapid bone repair and pain relief, allowing an early return to competition. In the case 2 patient, humeral shortening was identified. Handstand-position radiography revealed compensatory scapular movements, negating the need for surgical intervention. These findings highlight ESWT's potential in promoting bone repair and the utility of handstand-position radiography in assessing humeral length. Both methods provide innovative treatment approaches for proximal humeral epiphysiolysis in gymnasts.

Biomechanical Characteristics of Scapular and Glenohumeral Movements during Pitching Motion in Injury-prone College Baseball Pitchers

OBJECTIVES

The coordination of glenohumeral (GH) and scapular movements is central to the injury prevention of baseball pitchers. However, there is no objective data establishing the direct relationship between pitching injuries and associated GH and scapular movements. Therefore, this study demonstrated the biomechanical differences in the scapular and GH movements during pitching between injury-prone pitchers and healthy college baseball pitchers.

METHODS

A total of 30 collegiate baseball pitchers were classified into two groups according to their injury status: injury-prone group (n = 15) and control group (n = 15). We obtained pitching motion data using three-dimensional motion analysis technique.

RESULTS

The horizontal abduction angles of the GH joint during cocking and acceleration phases were considerably greater in the injury-prone pitchers (19.0° at stride foot contact [SFC], -4.0° at maximum external rotation [MER], and -0.3° at ball release) than those in healthy controls (11.7° at SFC, -10.0° at MER, and -6.9° at ball release). Additionally, in the cocking phase, the amount of angular change in the scapular external rotation (ER) was significantly smaller in the injury-prone group than that in the control group (mean difference, -13.0).

CONCLUSION

These results suggest that the injury-prone pitchers have less internal rotation of the scapula and a more horizontal abduction of the GH joint during the cocking and acceleration phases. Therefore, sports medicine practitioners may need to pay considerable attention to the coordination of scapular and GH horizontal movements during pitching for prevention of shoulder injuries.

Little League Shoulder and Subsequent Proximal Humeral Fracture in the Setting of Human Growth Hormone Use: A Case Report

CASE

A 16-year-old right-hand dominant male baseball player presented with little league shoulder in the setting of recombinant growth hormone utilization for growth hormone deficiency. After a prolonged treatment course, including physical therapy and throwing programs, the patient returned to baseball but suffered an ipsilateral proximal humerus fracture around the growth plate.

CONCLUSION

The occurrence of such an injury in the context of human growth hormone treatment merits consideration in youth athletes undergoing similar treatment regimens. Clinically, we recommend screening pediatric patients with sports-related epiphysiolysis for current or previous growth hormone use because of the possible prognostic implications of such treatment.

Increased Pitch Velocity Is Associated With Throwing Arm Kinetics, Injury Risk, and Ulnar Collateral Ligament Reconstruction in Adolescent, Collegiate, and Professional Baseball Pitchers: A Qualitative Systematic Review

PURPOSE

To assess the relationship between pitch velocity and throwing arm kinetics, injury, and ulnar collateral ligament reconstruction (UCLr) among high school, collegiate, and professional baseball pitchers.

METHODS

The Cochrane Database of Systematic Reviews, the Cochrane Central Register of Controlled Trials, PubMed (2008-2019), and OVID/MEDLINE (2008-2019) were queried for articles that reported on pitch velocity predicting throwing arm kinetics, injury, or UCLr. The Methodological Index for Non-randomized Studies checklist was used to evaluate the quality of all included studies. Descriptive statistics with ranges were used to quantify data where appropriate.

RESULTS

A total of 24 studies examining 2,896 pitchers, with Level of Evidence II-V were included. Intergroup analysis noted pitch velocity was significantly correlated with elbow varus torque in high school (R² = 0.36), collegiate (R² = 0.29), and professional (R² = 0.076) pitchers. Elbow distraction force was positively associated with ball velocity in interpitcher analyses of high school (R² = 0.373), professional (R² = 0.175), and mixed-cohort evaluations (R² = 0.624). Intragroup analysis demonstrated a strong association between pitch velocity and elbow varus torque (R² = 0.922-0.957) and elbow distraction force (R² = 0.910) in professional pitchers. Faster ball velocity was positively associated with a history of throwing arm injury (R² = 0.194) in nonadult pitchers. In 2 studies evaluating professionals, injured pitchers had faster pitch velocity before injury compared with uninjured controls (P = .014; P = .0354). The need for UCLr was positively correlated with pitch velocity (R² = 0.036) in professional pitchers. The consequences of UCLr noted little to no decrease in pitch velocity.

CONCLUSIONS

Professional baseball pitchers with faster pitch velocity may be at the greatest risk of elbow injury and subsequent UCLr, potentially through the mechanism of increased distractive forces on the medial elbow complex. When a pitcher ultimately undergoes UCLr, decreases in pitching performance are unlikely, but may occur, which should encourage pitchers to caution against maximizing pitch velocity.

LEVEL OF EVIDENCE

Level IV, systematic review of Level II-IV studies.

Effect of Pitching Restrictions and Mound Distance on Youth Baseball Pitch Counts

Background:

Studies have shown that higher pitch counts are directly related to a greater incidence of elbow and shoulder pain among youth baseball pitchers.

Purpose/Hypothesis:

The purpose of this study was to examine the effect of different pitching restriction rules on the number of pitches thrown in youth baseball leagues. We hypothesized that more pitches would be thrown in leagues with inning restrictions versus leagues with pitch count restrictions as well as in leagues with a longer mound distance (from pitching mound to home plate).

Study Design:

Cohort study; Level of evidence, 2.

Methods:

Pitch count data were collected for 2 consecutive years over a 10-week season from 3 different leagues of 9- to 12-year-old baseball players in a single city. The Eastern league had a pitch count restriction and 46-ft (14.02-m) mound distance. The Southeastern and South leagues’ pitching restrictions were based on innings per week. The Southeastern league had a 50-ft (15.24-m) mound distance, while the South league had a 46-ft mound distance. Comparisons of total seasonal pitches thrown were made of the 3 highest-volume pitchers on each team. League averages for each value were then compared utilizing analysis of variance with Bonferroni post hoc analysis. The number of pitchers in each league who threw >600 pitches per season was compared using the chi-square test.

Results:

No significant difference in seasonal pitch counts or innings pitched was noted between the Eastern and South leagues, which differed only in their pitching restrictions. The Southeastern league, with a longer mound distance, was found to have higher seasonal pitch counts per thrower (598 ± 195 pitches) than the South league (463 ± 198 pitches) for the 3 highest-volume throwers for each team (P = .004). The Southeastern league also had a significantly larger number of pitchers who threw >600 pitches per season (33 vs 20 for Eastern and 13 for South; P = .009).

Conclusion:

There was no significant difference in seasonal pitch counts when the leagues in this study differed based on pitching restrictions. However, the league with a greater mound distance (Southeastern) had higher seasonal pitch counts for the highest-volume throwers. Pitching restrictions based on pitch counts, as opposed to innings, may be advisable.

The influence of shoulder abduction and external rotation on throwing arm kinetics in professional baseball pitchers

BACKGROUND

The relationships between shoulder abduction and external rotation with peak kinetic values at the shoulder and elbow in professional baseball pitchers are not well established.

METHODS

Professional pitchers (n = 322) threw 8-12 fastballs under 3D motion analysis (480 Hz). Pitchers were stratified into quartiles by shoulder abduction and external rotation at distinct timepoints. Regression analyses were performed to quantify associations between shoulder position and kinetics.

RESULTS

Shoulder abduction remained relatively consistent throughout the pitch (foot contact-ball release: 85.5 ± 11.1-90.7 ± 8.4°); shoulder external rotation increased dramatically (foot contact-ball release: 30.8 ± 24.6-165.2 ± 9.7°). For every 10° increase in maximum shoulder rotation, shoulder superior force increased by 2.3% body weight (p < 0.01), shoulder distraction force increased by 5.9% body weight (p < 0.01), and ball velocity increased by 0.60 m/s (p < 0.01). Shoulder abduction was significantly associated with shoulder superior force at all timepoints but not with ball velocity (p > 0.05). For every 10° increase in shoulder abduction at ball release, shoulder superior force increased by 3.7% body weight (p < 0.01) and shoulder distraction force increased by 11.7% body weight (p < 0.01).

CONCLUSION

Increased shoulder abduction at ball release and increased maximum shoulder external rotation were associated with greater superior and distraction forces in the shoulder. Pitchers can consider decreasing shoulder abduction at later stages of the pitch to around 80° in order to minimize shoulder superior force, with no impact on ball velocity.

The Relationship Between Maximum Shoulder Horizontal Abduction and Adduction on Peak Shoulder Kinetics in Professional Pitchers

BACKGROUND

Repetitive horizontal shoulder abduction during pitching can cause increased contact between the posterosuperior aspect of the glenoid and the greater tuberosity of the humeral head, theoretically putting baseball pitchers at increased risk of shoulder internal impingement and other shoulder pathologies.

HYPOTHESIS

Increased shoulder horizontal abduction is associated with increased shoulder anterior force, while increased horizontal adduction is associated with increased shoulder distraction force.

STUDY DESIGN

Descriptive laboratory study.

LEVEL OF EVIDENCE

Level 4.

METHODS

A total of 339 professional baseball pitchers threw 8 to 10 fastball pitches using 3D motion capture (480 Hz). Pitchers were divided into 2 sets of quartiles based on maximum shoulder horizontal abduction and adduction. Elbow flexion, shoulder external rotation, and peak shoulder kinetics were compared between quartiles with post hoc linear regressions conducted for the entire cohort.

RESULTS

At maximum shoulder horizontal abduction, there was no difference in ball velocity between quartiles (P = 0.76). For every 10º increase in maximum shoulder horizontal abduction, shoulder anterior force decreased by 2.2% body weight (BW) (P < 0.01, B = -0.22, β = -0.38), shoulder adduction torque decreased by 0.5%BW × body height (BH) (P < 0.01, B = -0.05, β = -0.19), and shoulder horizontal adduction torque decreased by 0.4%BW × BH (P < 0.01, B = -0.04, β = -0.48). For every 10º increase in maximum shoulder horizontal adduction, shoulder anterior force increased by 2%BW and ball velocity decreased by 1.2 m/s (2.7 MPH).

CONCLUSION

Professional pitchers with the least amount of maximum horizontal adduction had faster ball velocity and decreased shoulder anterior force. Pitchers with greater maximum shoulder horizontal abduction had decreased shoulder anterior force, shoulder adduction torque, and shoulder horizontal adduction torque. To maximize ball velocity as a performance metric while minimizing shoulder anterior force, pitchers can consider decreasing maximum shoulder adduction angles at later stages of the pitch.

CLINICAL RELEVANCE

Identifying risk factors for increased throwing shoulder kinetics (ie, shoulder anterior force, shoulder adduction torque) has potential implications in injury prevention. Specifically, mitigating shoulder anterior forces may be beneficial in reducing risk of injury.

Disabled Throwing Shoulder 2021 Update: Part 1-Anatomy and Mechanics

The purpose of this article is to provide updated information for sports health care specialists regarding the Disabled Throwing Shoulder (DTS). A panel of experts, recognized for their experience and expertise in this field, was assembled to address and provide updated information on several topics that have been identified as key areas in creating the DTS spectrum. Each panel member submitted a concise presentation on one of the topics within these areas, each of which were then edited and sent back to the group for their comments and consensus agreement in each area. Part 1 presents the following consensus conclusions and summary findings regarding anatomy and mechanics, including: 1) The current understanding of the DTS identifies internal impingement, resulting from a combination of causative factors, as the final common pathway for the great majority of the labral pathoanatomy; 2) intact labral anatomy is pivotal for glenohumeral stability, but its structure does not control or adapt well to shear or translational loads; 3) the biceps plays an active role in dynamic glenohumeral stability by potentiating "concavity compression" of the glenohumeral joint; 4) the ultimate function of the kinetic chain is to optimize the launch window, the precise biomechanical time, and position for ball release to most effectively allow the ball to be thrown with maximum speed and accuracy, and kinetic chain function is most efficient when stride length is optimized; 5) overhead throwing athletes demonstrate adaptive bony, capsular, and muscular changes in the shoulder with repetitive throwing, and precise measurement of shoulder range of motion in internal rotation, external rotation, and external rotation with forearm pronation is essential to identify harmful and/or progressive deficits. LEVEL OF EVIDENCE: Level V, expert opinion.

An anatomic and 3D study of the development of the proximal humeral physis

PURPOSE

During maturation, the ossification centers of the proximal humerus form a characteristic pattern consisting of a metaphyseal peak and corresponding epiphyseal valley. The surface topographies of the metaphyseal peak and epiphyseal valley are not well described and may have variation with age and structural importance to the pathogenesis of proximal humeral epiphysiolysis.

METHODS

High-resolution 3-dimensional surface scans of 24 cadaveric proximal humeral epiphyses and metaphyses in specimens aged 3 to 18 years were obtained. Computer modeling software was used to measure the peak height of the metaphysis and maximal depth of the epiphysis relative to a perpendicular line drawn across the proximal humeral physis.

RESULTS

The metaphyseal peak had a mean height of 12.7 ± 1.6 mm while the epiphyseal valley had a mean depth of 13.1 ± 2.1 mm, both consistently positioned in the posterolateral quadrant. Both the absolute metaphyseal peak height (R² = 0.536; p < 0.001) and absolute epiphyseal valley depth (R² = 0.524; p < 0.001) increase with advancing age. Multiple linear regression analysis demonstrated that normalized metaphyseal peak height + sex (adjusted R² = 0.408; p < 0.002) correlated more with age than normalized epiphyseal valley depth + sex (adjusted R² = 0.128; p < 0.091).

CONCLUSION

Prominence of the metaphyseal peak and epiphyseal valley both increase with advancing age, with a lower correlation between normalized sizes with age as compared to the absolute sizes, suggesting that these structures stay relatively proportional with growth.

The Thrower's Shoulder

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The thrower's shoulder has been a subject of great interest for many decades. Different theories have been proposed to clarify the pathophysiology, clinical presentation, and treatment options for this condition. In this review article, we summarize the relevant anatomy and pathophysiology and how these translate into signs, symptoms, and imaging findings. Also, a historical review of the treatment methodologies in the setting of an evolving concept is presented.

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The initial event in the cascade is thickening and contracture of the posteroinferior capsule resulting from repetitive tensile forces during the deceleration phase of throwing. This is known as "the essential lesion" and is clinically perceived as glenohumeral internal rotation deficit (GIRD), and a Bennett lesion may be found on radiographs.

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Change in the glenohumeral contact point leads to a series of adaptations that are beneficial for the mechanics of throwing, specifically in achieving the so-called "slot," which will maximize throwing performance.

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The complexity of the throwing shoulder is the result of an interplay of the different elements described in the cascade, as well as other factors such as pectoralis minor tightness and scapular dyskinesis. However, it is still unclear which event is the tipping point that breaks the balance between these adaptations and triggers the shift from an asymptomatic shoulder to a painful disabled joint that can jeopardize the career of a throwing athlete. Consequences are rotator cuff impingement and tear, labral injury, and scapular dyskinesis, which are seen both clinically and radiographically.

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A thorough understanding of the pathologic cascade is paramount for professionals who care for throwing athletes. The successful treatment of this condition depends on correct identification of the point in the cascade that is disturbed. The typical injuries described in the throwing shoulder rarely occur in isolation; thus, an overlap of symptoms and clinical findings is common.

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The rationale for treatment is based on the pathophysiologic biomechanics and should involve stretching, scapular stabilization, and core and lower-body strengthening, as well as correction of throwing mechanics, integrating the entire kinetic chain. When nonoperative treatment is unsuccessful, surgical options should be tailored for the specific changes within the pathologic cascade that are causing a dysfunctional throwing shoulder.

Torso kinematic patterns associated with throwing shoulder joint loading and ball velocity in Little League pitchers

The purpose of this study was to investigate the associations between kinematic patterns of the torso segment and shoulder joint loading as well as pitching performance in youth pitchers. Twenty-four Little League pitchers threw fastballs while motion capture and force plate data were collected and ball speed was measured with a radar gun. Three-dimensional torso segment kinematics (absolute angles and angular velocities) and shoulder net joint moments (NJM) and forces were calculated. The time-series kinematic data were used as inputs to a principal components analysis to extract torso movement patterns. Associations between torso movement patterns and discrete peak shoulder NJM, compressive force, and ball speed were investigated with nonparametric correlations. Torso segment motion patterns related to forward flexion, lateral flexion (away from pitching arm), and axial rotation and rotational velocities were associated with shoulder joint kinetics and ball speed. In addition, excessive axial (transverse plane) torso rotation at ball release correlated positively with shoulder joint loads but not ball speed, which may indicate the prospect for decreasing joint kinetics while maintaining pitching performance through targeted interventions. These results provide a deeper understanding about the interrelationships between torso kinematic patterns, shoulder kinetics, and pitching performance.

Reliability of an Observational Biomechanical Analysis Tool in Adolescent Baseball Pitchers

BACKGROUND

Improper pitching mechanics are a risk factor for arm injuries. While 3-dimensional (3D) motion analysis remains the gold standard for evaluation, most pitchers and clinicians do not have access to this costly technology. Recent advances in 2-dimensional (2D) video technology provide acceptable resolution for clinical analysis. However, no systematic assessment tools for pitching analysis exist.

PURPOSE

To determine the reliability of the Assessment of biomeChanical Efficiency System (ACES) screening tool using 2D video analysis to identify common biomechanical errors in adolescent pitchers.

STUDY DESIGN

Cross-sectional.

METHODS

Adolescent baseball pitchers underwent analysis using 2D video in indoor settings. Observational mechanics were collected using a 20-item scoring tool (ACES) based on 2D video analysis. Fleiss' kappa, interclass correlation coefficients (ICC), and frequencies were used to examine intra-/interrater reliability based on common pitching errors.

RESULTS

Twenty asymptomatic pitchers ages 12-18 years were included. Total ACES scores ranged from 1 to 13, normally distributed. ACES total score demonstrated excellent intra-rater reliability within each rater (ICC for rater 1 = 0.99 (95% CI; 0.98, 0.99); ICC for rater 2 = 0.94; 95% CI: 0.84, 0.97); ICC for rater 3 = 0.98 (95% CI: 0.96, 0.99)). There was excellent interrater reliability across the trials and raters (ICC = 0.91; 95% CI: 0.82, 0.96). The ACES tool demonstrated acceptable kappas for individual items and strong ICC 0.91 (95% CI: 0.82, 0.96) for total scores across the trials. Regarding identification of biomechanical errors, "front side position" was rated erroneous in 84/120 ratings (70%), stride length in 52/120 ratings (43.3%) and lead hip position in 53/120 ratings (44.2%).

CONCLUSIONS

The 20-item ACES scoring tool with 2D video analysis demonstrated excellent intra- and interrater reliability when utilized by raters of different musculoskeletal disciplines. Future studies validating 2D vs. 3D methodology are warranted before ACES is widely disseminated and utilized for adolescent pitchers. ACES is a practical and reliable clinical assessment tool utilizing 2D video analysis for coaches, instructors, and sports medicine providers to screen adolescent pitchers for common biomechanical errors.

LEVEL OF EVIDENCE

3b.

Development and internal validation of a humeral torsion prediction model in professional baseball pitchers

BACKGROUND

Humeral torsion (HT) has been linked to pitching arm injury risk after controlling for shoulder range of motion. Currently measuring HT uses expensive equipment, which inhibits clinical assessment. Developing an HT predictive model can aid clinical baseball arm injury risk examination. Therefore, the purpose of this study was to develop and internally validate an HT prediction model using standard clinical tests and measures in professional baseball pitchers.

METHODS

An 11-year (2009-2019) prospective professional baseball cohort was used for this study. Participants were included if they were able to participate in all practices and competitions and were under a Minor League Baseball contract. Preseason shoulder range of motion (external rotation [ER], internal rotation [IR], horizontal adduction [HA]) and HT were collected each season. Player age, arm dominance, arm injury history, and continent of origin were also collected. Examiners were blinded to arm dominance. An a priori power analysis determined that 244 players were needed for accurate prediction models. Missing data was low (<3%); thus, a complete case analysis was performed. Model development followed the transparent reporting of a multivariable prediction model for individual prognosis or diagnosis (TRIPOD) recommendations. Regression models with restricted cubic splines were performed. Following primary model development, bootstrapping with 2000 iterations were performed to reduce overfitting and assess optimism shrinkage. Prediction model performance was assessed through root mean square error (RMSE), R², and calibration slope with 95% confidence intervals (CIs). Sensitivity analyses included dominant and nondominant HT.

RESULTS

A total of 407 professional pitchers (age: 23.2 [standard deviation 2.4] years, left-handed: 17%; arm history prevalence: 21%) participated. Predictors with the highest influence within the model include IR (0.4, 95% CI 0.3, 0.5; P < .001), ER (-0.3, 95% CI -0.4, -0.2; P < .001), HA (0.3, 95% CI 0.2, 0.4; P < .001), and arm dominance (right-handed: -1.9, 95% CI -3.6, -0.1; P = .034). Final model RMSE was 12, R² was 0.41, and calibration was 1.00 (95% CI 0.94, 1.06). Sensitivity analyses demonstrated similar model performance.

CONCLUSIONS

Every 3° of IR explained 1° of HT. Every 3° of ER explained 1° less of HT, and every 7° of HA explained 1° of HT. Right-handers had 2° less HT. Models demonstrated good predictive performance. This predictive model can be used by clinicians to infer HT using standard clinical test and measures. These data can be used to enhance professional baseball arm injury examination.

Shoulder External Rotational Properties During Physical Examination Are Associated With Injury That Requires Surgery and Shoulder Joint Loading During Baseball Pitching

BACKGROUND

Throwing arm injuries are common because of the demand on the shoulder. The shoulder is qualitatively checked regularly by team physicians. Excessive instability and joint loading in baseball pitching are risk factors for throwing arm injuries. Knowledge of shoulder flexibility, range of motion, and joint loading may provide new insights for treatments to reduce the likelihood of injury incidence.

PURPOSE

To investigate the relationship among injuries, shoulder external rotational properties, and shoulder joint loading in baseball pitchers.

STUDY DESIGN

Descriptive laboratory study.

METHODS

Pitching kinetics, shoulder rotational tests, and self-reported injury questionnaires were used to study 177 collegiate baseball pitchers. Pitching motion data were collected at 240 Hz using a motion capture system. A custom program calculated the shoulder joint loading. The shoulder rotational test quantitatively records shoulder range of motion and flexibility using a custom-made wireless device. Self-reported injury questionnaires were filled out during tests and yearly follow-ups. The total length of the study was 5 years. Analysis of variance, chi-square, and regression tests were performed to compare differences among groups and detect correlations with surgery and shoulder joint loadings.

RESULTS

There were significant differences in shoulder flexibility among surgery groups. Shoulder external rotational properties during physical examination were significantly associated with shoulder joint loading in baseball pitching. High shoulder external rotation was associated with 14% to 36% lower shoulder posterior force and adduction, internal rotation, and horizontal adduction torque (P < .05). High shoulder flexibility was associated with 13% higher anterior force (P < .05). High shoulder external rotation before external rotation torque was applied was associated with 13% to 33% lower shoulder inferior force and adduction, internal rotation, and horizontal adduction torque (P < .05). There were no significant differences in shoulder joint loading among the surgery groups.

CONCLUSION

Shoulder injuries that require surgery were associated with shoulder external rotation flexibility. High shoulder external rotation may be advantageous because it lowers the force and torque on the shoulder joint.

CLINICAL RELEVANCE

The ability to understand shoulder external rotational properties, joint loading, and injury during baseball pitching helps further our understanding of injury mechanisms. The shoulder rotational test should be used as a screening tool to identify players at risk.

Intra- versus inter-pitcher comparisons: Associations of ball velocity with throwing-arm kinetics in professional baseball pitchers

BACKGROUND

The association between ball velocity and elbow varus torque has shown differences when evaluated within a single pitcher and within a cohort. The impact of increasing ball velocity on additional throwing-arm kinetics, in particular shoulder distraction forces, with intra- vs. inter-pitcher evaluations has not been evaluated, even though these kinetic measures have been implicated in injury risk. The purpose of this study was to compare intra- vs. inter-pitcher relationships between ball velocity and all major kinetics at the shoulder and elbow in professional pitchers.

METHODS

A total of 323 professional baseball pitchers threw 8-12 fastball pitches while simultaneously being evaluated with 3-dimensional motion-capture technology (480 Hz). A linear regression analysis was performed to evaluate pitch velocity as a predictor of peak kinetic values at the shoulder and elbow among pitchers. A linear mixed model with random intercepts was then created to evaluate ball velocity as a predictor of peak kinetic values when comparing pitches within an individual pitcher.

RESULTS

91 pitchers were included in the analyses. Ball velocity among pitchers had weak correlations with shoulder distraction force (R² = 0.228, P < .001) and elbow distraction force (R² = 0.175, P < .001). Within an individual pitcher, strong correlations (R² > 0.85) were observed for (1) shoulder internal rotation torque (P < .001), (2) shoulder horizontal adduction torque (P = .006), (3) shoulder superior force (P < .001), (4) shoulder anterior force (P < .001), (5) elbow varus torque (P < .001), (6) elbow medial force (P < .001), (7) elbow anterior force (P < .001), (8) elbow flexion torque (P < .001), (9) shoulder distractive force (P < .001), and (10) elbow distractive force (P < .001).

CONCLUSION

Faster pitch velocity is a weak predictor of shoulder and elbow distraction forces experienced among professional pitchers. However, when controlling for an individual pitcher, peak kinetics at the shoulder and elbow can be strongly predicted by ball velocity. Therefore, the assumption that higher peak throwing-arm kinetic values are experienced by pitchers with faster ball velocity is likely an inappropriate assumption among pitchers but may be correct for each player who increases pitch velocity.

The Effects of Physical Activity on Physeal and Skeletal Development

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There is increasing evidence in the literature regarding the important health impact of and risk factors for injury in youth sport.

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Increasing pediatric and adolescent activity intensity, such as is seen in earlier single-sport focus and specialization, may be associated with morphological changes in the growing skeleton.

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Chronic subacute injury to the developing physes in the active child can lead to stress on the growth plate and surrounding tissues that induces developmental morphological changes in the joint.

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There is evidence to suggest that frequent participation in sports that place particular stress across the physes of the proximal humerus, the proximal femur, and the distal radius can be associated with an increased risk of inducing developmental and morphological changes that could lead to future joint dysfunction and premature degeneration.

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Additional research is necessary to better define the pathoetiology of activity-mediated morphological changes, as well as to create and validate parameters for safe involvement in competitive physical activities.

Investigation of Ultrasound as a Diagnostic Imaging Modality for Little League Shoulder

Objective Ultrasound (US) is an established imaging modality in adult sports medicine but is not commonly used in the diagnosis of pediatric sports conditions, such as Little League shoulder (LLS). This study was conducted to determine the reliability of US measurement of width of the physis at the proximal humerus in diagnosed LLS and to compare US to radiography (RA) in detecting a difference between the affected (dominant) (A) and unaffected (U) shoulders.

Materials and Methods Ten male baseball players diagnosed with LLS were enrolled in the study. US images of the proximal humeral physis at the greater tuberosity of both shoulders were obtained by an US-trained sports medicine physician, and the physeal width was measured. Blinded to prior measurements, a separate physician performed measurements on the stored US images. Measurements were compared with RA on the anteroposterior (AP) view for both A and U at the time of the initial visit and for A at follow-up.

Results The physeal width (mm) at A and U at the initial visit averaged 5.94 ± 1.69 and 4.36 ± 1.20 respectively on RA, and 4.15 ± 1.12 and 3.40 ± 0.85 on US. Median difference of averaged US measurements between A and U at initial evaluation was 0.75 mm (p = 0.00016). A linear model showed US measurements to be predictive of RA on A (R2 = 0.51) and U (R2 = 0.48).

Conclusion US was able to reliably measure the width of the proximal humeral physis and detect a difference between A and U. US correlated well with RA (standard for LLS). US should be considered by the US-trained physician for the diagnosis of LLS.

Shoulder Range of Motion Deficits in Youth Throwers Presenting With Elbow Pain

BACKGROUND

Glenohumeral internal rotation deficit (GIRD) and total arc of motion difference (TAMD) have been associated with elbow injuries in throwing athletes.

HYPOTHESIS

Youth pitchers with elbow pain will have greater GIRD and TAMD compared with youth pitchers without elbow pain.

STUDY DESIGN

Cross-sectional study.

LEVEL OF EVIDENCE

Level 3.

METHODS

Glenohumeral range of motion of 25 consecutive throwing athletes presenting with elbow pain and that of a matched control group of 18 asymptomatic throwing athletes were compared. Bilateral glenohumeral internal rotation, external rotation, and horizontal adduction at 90° were measured and GIRD and TAMD were then calculated. An analysis of variance was performed to compare range of motion between throwers with and without elbow pain.

RESULTS

The average GIRD of the elbow pain group was 32.7° compared with 14.5° in the control group (P < 0.05). The average TAMD in the elbow pain group was 28.3° compared with 6.7° in the control group (P < 0.05). GIRD and TAMD were present in 88% (22 of 25) and 96% (24 of 25) of the elbow pain group versus 33.3% (6 of 18) and 55.6% (10 of 18) of the control group, respectively.

CONCLUSION

Compared with asymptomatic youth pitchers, those presenting with elbow pain have a statistically significant GIRD and TAMD.

CLINICAL RELEVANCE

This study suggests that a GIRD and TAMD may predispose youth pitchers to present with symptomatic elbow pain.

The association between gird and overhead throwing biomechanics in cricket

The development of GIRD is a well-documented adaptation associated with repetitive overhead throwing in numerous sports. In occurrence with total rotational range of motion deficit, GIRD is considered pathological and increases shoulder injury risk. While cricketers demonstrate these deficits in rotational range; the association between GIRD and overhead throwing has yet to be explored. Therefore, the aim of this study was to determine the relationship between GIRD and overhead throwing biomechanics in cricketers. Passive shoulder rotational range of motion was measured in 15 cricketers (elite = 8, amateur = 7). Kinetic and kinematic data were obtained during overhead throws from a stationary and run-up approach. Linear regression was used to determine potential relationships between GIRD and discrete shoulder kinetics for both throwing approaches. One-dimensional statistical parametric mapping regression was conducted to assess relationships between GIRD and throwing kinematics. When throwing overhead from a stationary position, GIRD was associated with reduced hip abduction during the preparatory arc (p = 0.002); superior shoulder (p = 0.003) and elbow compressive (p = 0.009) forces, at cocking. In addition, GIRD was associated with increased posterior shoulder force during arm deceleration for both stationary (p = 0.013) and run-up approaches (p = 0.03) to overhead throwing. Cricketers with GIRD utilise a shorter stride, creating early pelvic rotation and a slow throwing arm with an associated reduction in forces about the shoulder and elbow at cocking, when throwing from a stationary position. Further, overload of the posterior shoulder occurs during arm deceleration, irrespective of throwing approach. These findings highlight potential shoulder injury risk.

Diagnosis and Management of Little League Shoulder: A Systematic Review

Background:

Little League shoulder (LLS) is an overuse injury characterized by throwing-related pain that commonly presents in adolescent male athletes. Investigations into the optimal duration of rest from throwing and protocols for graduated return to sports (RTS) are lacking.

Purpose:

To summarize the current literature with respect to the diagnosis, management, RTS, and return to throwing for LLS.

Design:

Systematic review; Level of evidence, 4.

Methods:

The databases EMBASE, MEDLINE, and PubMed were searched between inception and April 22, 2020. References of retrieved records were reviewed for potentially eligible studies. English-language studies that reported the diagnosis and/or management of LLS in children or adolescents were included. Studies of animals or cadavers, review articles, and non—peer reviewed records were excluded. Data were summarized narratively using descriptive statistics.

Results:

Overall, 23 studies (21 level 4 studies, 2 level 3 studies) met the criteria for a total of 266 participants with a weighted mean age of 12.8 years (range, 7.4-17 years). Treatment recommendations evolved from prolonged rest and complete cessation of throwing to shorter periods of rest and graduated RTS. Less than half (11/23) of studies reported specific criteria to RTS; 1 case report discussed a coaching strategy to resume throwing, and 1 case report discussed a regimented throwing program. The proportion of participants returning to any sport participation was 94.0% (n = 157/167). The proportion returning to their preinjury level of sport was 92.5% (n = 123/133). Upon RTS, 18.7% (n = 35/187) of participants experienced a recurrence of symptoms. Premature closure of the epiphysis was reported in 1 participant.

Conclusion:

Young athletes with LLS may return to play after a period of rest, and a high proportion return to their preinjury level of sport. Further prospective studies are warranted to develop evidence-based, graduated RTS protocols and to better capture any long-term sequelae of the condition.

Physeal injury in a skeletally immature male athlete

A 12-year-old skeletally immature male athlete presented for evaluation with acute bilateral knee pain. Initial radiographs revealed subtle lucency of the medial proximal tibial physis and MRI was recommended. On MRI, broad-based intravasation of the physis into the proximal femoral and tibial physes was observed. This represented physeal widening, a phenomenon that has been observed in skeletally immature athletes presenting for acute knee pain. While such changes to the physis may be quite prominent on MRI, conventional radiographic findings may be much more subtle. As many causes of chronic knee pain in this population are managed with active rehabilitation, a high index of suspicion for this diagnosis in the presence of physeal abnormalities may warrant evaluation with MRI. The literature suggests this pathology will resolve with rest, but, if weight-bearing activities are continued, there is a risk for significant growth abnormalities.

Junior and Collegiate Tennis Players Display Similar Bilateral Asymmetries of Humeral Retroversion

CONTEXT

Overhead throwing athletes consistently display significant bilateral differences in humeral retroversion (HRV). However, there is limited evidence regarding HRV asymmetries in tennis players despite similarities between the overhead throw and tennis serve.

OBJECTIVE

To determine if junior and collegiate tennis players demonstrate bilateral differences in HRV, and whether the magnitude of the side-to-side difference (HRVΔ) was similar across different age groups.

DESIGN

Cross-Sectional Study Setting: Field-Based Patients or Other Participants: Thirty-nine healthy tennis players were stratified into three age groups: Younger Juniors (n = 11; age = 14.5 ± 0.5 years), Older Juniors (n = 12; age = 17.1 ± 0.9 years), and Collegiate (n = 16; age = 19.6 ± 1.2 years).

MAIN OUTCOME MEASURES

Three-trial means were calculated for HRV for the dominant and nondominant limbs, and HRVΔ was calculated by subtracting the mean of the nondominant side from the dominant side. Paired-sample t-tests were utilized to determine bilateral differences in HRV, while a one-way ANOVA was used to compare HRVΔ between groups.

RESULTS

For all three groups, HRV was significantly greater in the dominant arm compared to the nondominant arm (Younger Juniors: dominant = 62.8° ± 9.1° vs nondominant = 56.3° ± 6.8°, P = .039; Older Juniors: dominant = 75.5° ± 11.2° vs nondominant = 68.6° ± 14.2°, P = .043; Collegiate: dominant = 71.7° ± 8.5° vs nondominant = 61.2° ± 6.9°, P = .001). However, no significant differences were detected in HRVΔ when compared across age groups (P = .511).

CONCLUSIONS

Consistent with studies involving overhead throwing athletes, tennis players demonstrated significantly greater measures of HRV in the dominant limb. Further, the development of HRV asymmetries appear to have occurred prior to the teenage years as no changes were observed in HRVΔ between age groups.

Distal Femoral Physeal Bar Resection Combined With Guided Growth for the Treatment of Angular Limb Deformity Associated With Growth Arrest: A Preliminary Report

PURPOSE

Distal femoral growth arrest can result in progressive deformities and functional disability. The treatment is challenging given the significant growth potential of the distal femoral physis. This study addresses the short-term outcomes after distal femoral physeal bar resection combined with guided growth for the treatment of angular limb deformity.

METHODS

We conducted a retrospective analysis of patients treated with distal femoral physeal bar resection, fat graft interposition, and growth modulation with a tension-band plate. Data recorded included patient demographics, growth arrest cause, physeal bar size, time-to-surgery, details of the operative procedure, and complications. The mechanical axis zones, tibiofemoral angle, and the anatomic lateral distal femoral angle were assessed on 51-inch anteroposterior standing radiographs.

RESULTS

Five patients (3 male individuals) with valgus (n=4) and varus deformities (n=1) due to physeal arrests of the distal femur were analyzed. The cause of the physeal arrest was trauma (n=3) and infection (n=2). The average age at the time of surgery was 6.6 years (range: 2 to 11 y). Average size of the physeal bar was 413.4 mm, which represented 16.8% of the total distal femoral physis (range: 12% to 26%). Four of the 5 patients had a total correction of the deformity in 14.3 months (range: 9 to 22 mo). One patient required correction by osteotomy and external fixation. Postoperatively, 1 patient presented no improvement, and 4 had restoration of the longitudinal bone growth and alignment. Two patients had rebound valgus: one is being observed and another has undergone a repeat guided growth procedure.

CONCLUSIONS

Distal femoral physeal bar resection combined with tension-band hemiepiphysiodesis provides a viable option for the correction of angular deformities associated with physeal arrest. Longer follow-up is required to evaluate future growth of the distal femoral physis after this combined procedure.

LEVEL OF EVIDENCE

Level IV-therapeutic study.

Does Youth Baseball Result in Morphologic Changes of the Lateral Elbow? A Prospective MRI Study

BACKGROUND

Stress from overhead throwing results in morphologic changes to the shoulder in youth baseball players. With greater valgus torque stresses, the elbow experiences injuries specifically attributed to throwing. However, no previous work that we know of has assessed throwing-related morphologic changes of the elbow without associated conditions.

QUESTIONS/PURPOSES

(1) Do children who play competitive baseball have enlargement or overgrowth of their radial head shape and/or capitellum compared with the nondominant elbow on MRI? (2) Do children who stop playing year-round baseball have less enlargement of the lateral elbow structures than children who maintain a high level of play?

METHODS

A prospective study was conducted between 2015 and 2018 on preadolescent boys who underwent voluntary MRI of their bilateral elbows before the start of the spring baseball season. Twenty-six children agreed to participate out of a four-team league that was asked to participate; their first MRI was obtained at a mean (range) age of 12 years (10 to 13). We also obtained their history related to throwing and performed a physical examination. Players had a mean of 5.6 years of playing before their first MRI, and half the children (13 of 26) were year-round baseball players. Sixty-two percent (16 of 26) reported being either or both a pitcher or catcher as their primary position. No child was excluded from participation. Three years later, these boys were asked to return for repeat MRI and physical examinations. Fifty-eight percent (15 of 26) of players were still playing at the 3-year MRI. Continued play or new onset of pain was documented. Radiographic measurements were then compared between dominant and nondominant arms, and the differences of these changes were compared between those who had continued playing during the study period and those who had quit. The measurements were made in all three planes of the radial head and capitellum, both osseous and cartilaginous. Measurement intrarater and interrater reliability were in the good-to-excellent range (intraclass correlation coefficient 0.77 to 0.98).

RESULTS

When we compared dominant and nondominant arms, we found there was no dominant arm overgrowth (difference between baseline and 3-year measurements) in any measurement; for example, sagittal capitellum measurements in dominant arms were 2.5 ± 1.1 mm versus non-dominant arms: 2.8 ± 1.1 mm (mean difference -0.23 [95% CI -0.55 to 0.08]; p = 0.13). There was only undergrowth of the cartilaginous axial diameter of the radial head (change in dominant: 2.5 ± 1.3 mm; change in nondominant: 3.2 ± 1.7 mm; mean difference -0.64 mm [95% CI -1.2 to -0.06]; p = 0.03). There was no enlargement of the lateral elbow structures when children who continued to play were compared with children who stopped playing; for example, the difference in the bone-only growth ratio of the sagittal radial head to humerus of those still playing was 0.001 ± 0.03 and it was 0.01 ± 0.03 for those not playing (mean difference -0.01 [95% CI -0.04 to 0.01]; p = 0.29).

CONCLUSION

In healthy children who play baseball for multiple years between the ages of 6 to 11 years, continued torque at the elbow from throwing does not result in morphologic changes as it does in the shoulder. Despite evidence that injuries and surgery because of long-term participation in a throwing sport results in a larger radial head and capitellum, our study presents evidence that outside an injured elbow, throwing alone does not appear to change the morphology of the lateral elbow. Therefore, changes to the radial head size could presuppose other elbow pathology and future study could be performed to better evaluate the correlation.

LEVEL OF EVIDENCE

Level I, prognostic study.

Relationship between humeral retroversion and baseball positions during elementary and junior-high school

BACKGROUND

Humeral retroversion is greater in the dominant shoulder than in the nondominant shoulder in baseball players. However, the effect of different baseball positions during childhood on humeral retroversion remains unknown. The purpose of this study was to investigate the following: (1) the relationship between humeral retroversion and baseball positions played during elementary and junior-high schools; (2) the association between humeral retroversion and the prevalence of pain during the medical checkup and self-reported history of injuries in the dominant shoulder or elbow.

METHODS

We enrolled 149 male high-school baseball players who started playing baseball in elementary school. The subjects were classified into 3 groups according to their baseball positions in elementary and junior-high schools. All participants completed questionnaires regarding their current and past positions, current incidence and history of injuries in their shoulder or elbow joints, and the age they started playing baseball. Shoulder range of motion, humeral retroversion on ultrasonographic-assisted measurement, and the association between humeral retroversion and shoulder and elbow pain were evaluated.

RESULTS

Humeral retroversion was significantly greater in the dominant shoulder than in the nondominant shoulder in all groups (P < .001). In addition, humeral retroversion in the dominant shoulder was significantly greater in players who were pitchers in both elementary and junior-high schools than in those who were fielders during both periods (96.2° and 89.4°, respectively; P = .02). Humeral retroversion in the dominant shoulder was positively correlated (P = .005, r = 0.23) with the length of career as a pitcher during elementary and junior-high schools. Humeral retroversion was not correlated with the prevalence of pain during the medical checkup or self-reported history of injuries in the dominant shoulder or elbow (P values ranging from 0.09-0.99).

CONCLUSION

These results suggest that playing baseball as a pitcher during elementary school and junior-high school affects the increase in humeral retroversion in the dominant shoulder. Increased humeral retroversion in the dominant shoulder by repetitive throwing motion is an adaptive change, rather than a pathologic change.

Single Sport Specialization in the Skeletally Immature Athlete: Current Concepts

Youth sport participation patterns have drastically changed over the past two decades. Increasingly, young individuals are specializing in single sport while skeletally immature. Sport specialization in the growing athlete has profound effects on performance, short- and long-term injury risks, and joint health. Evidence continues to mount as the detrimental effects of this trend on the immature athlete. The knee, shoulder, and elbow of these young athletes are particularly affected by this emphasis on skill-based sporting activity as opposed to generalized fitness and participation. An understanding of the epidemiology of sport participation, particularly financial impacts, and the effects on elite sport performance are critical so that the clinician can effectively educate athletes, parents, and coaches.

Peak horizontal ground reaction forces and impulse correlate with segmental energy flow in youth baseball pitchers

The purpose of this study was to determine associations between horizontal ground reaction force (GRF) kinetics and energy flow (EF) variables in youth baseball players. Twenty-four youth baseball players pitched fastballs in an indoor laboratory while motion capture and force plate data were collected. Horizontal GRF variables were extracted (peak GRF and GRF impulse) while EF was calculated by integrating magnitudes of mechanical powers transferred into and out of the pelvis, trunk, and arm segments via joint force power (JFP) and joint moment power (JMP) components. Peak propulsive GRF of the drive (back) leg correlated with EF into proximal segments, whereas peak braking GRF of the stride (lead) leg correlated with EF into distal segments. Furthermore, peak GRF of the drive leg and GRF impulse of both legs correlated with the JFP components of EF into the pelvis and trunk segments. In contrast, peak GRF and GRF impulse of the stride leg both correlated with the JMP components of EF into the arm segment. These results suggest that horizontal GRF impulse from the drive and stride leg contribute to EF between major segments of the lower and upper extremity. In addition, these results also suggest that propulsion kinetics of the drive leg play a role in transferring linear power via the pelvis and trunk segments in the throwing direction of the pitch, whereas braking kinetics of the stride leg play a role in creating rotational power that is transferred between the trunk and arm segment via the shoulder joint.

Youth Single-Sport Specialization in Professional Baseball Players

Background:

An increasing number of youth baseball athletes are specializing in playing baseball at younger ages.

Purpose:

The purpose of our study was to describe the age and prevalence of single-sport specialization in a cohort of current professional baseball athletes. In addition, we sought to understand the trends surrounding single-sport specialization in professional baseball players raised within and outside the United States (US).

Study Design:

Cross-sectional study; Level of evidence, 3.

Methods:

A survey was distributed to male professional baseball athletes via individual team athletic trainers. Athletes were asked if and at what age they had chosen to specialize in playing baseball at the exclusion of other sports, and data were then collected pertaining to this decision. We analyzed the rate and age of specialization, the reasons for specialization, and the athlete’s perception of injuries related to specialization.

Results:

A total of 1673 professional baseball athletes completed the survey, representing 26 of the 30 Major League Baseball (MLB) organizations. Less than half (44.5%) of professional athletes specialized in playing a single sport during their childhood/adolescence. Those who reported specializing in their youth did so at a mean age of 14.09 ± 2.79 years. MLB players who grew up outside the US specialized at a significantly earlier age than MLB players native to the US (12.30 ± 3.07 vs 14.89 ± 2.24 years, respectively; P < .001). Additionally, MLB players raised in the US recalled a significantly higher incidence of sustaining an injury attributed to specializing in baseball than MLB athletes raised outside the US (27.7% vs 20.6%, respectively; P = .05).

Conclusion:

This study challenges the current trends toward early youth sport specialization, finding that the majority of professional baseball athletes studied did not specialize as youth and that those who did specialize did so at a mean age of 14 years. With the potential cumulative effects of pitching and overhead throwing on an athlete’s arm, the trend identified in this study toward earlier specialization within baseball is concerning.

The Relationship Between Humeral Torsion and Arm Injury in Baseball Players: A Systematic Review and Meta-analysis

CONTEXT

Humeral torsion (HT) has been linked to various injuries and benefits. However, the exact interplay between HT, shoulder range of motion (ROM), competition level differences, and injury risk is unclear.

OBJECTIVE

To determine the relationship between HT, ROM, and injury risk in baseball players. Secondarily, to determine HT based on competition level.

DATA SOURCES

PubMed, Embase, Web of Science, CINAHL, and Cochrane databases were searched from inception until November 4, 2018.

STUDY SELECTION

Inclusion criteria consisted of (1) HT measurements and (2) arm injury or shoulder ROM.

STUDY DESIGN

Systematic review.

LEVEL OF EVIDENCE

Level 3.

DATA EXTRACTION

Two reviewers recorded patient demographics, competition level, HT, shoulder ROM, and injury data.

RESULTS

A total of 32 studies were included. There was no difference between baseball players with shoulder and elbow injuries and noninjured players (side-to-side HT difference: mean difference [MD], 1.75 [95% CI, -1.83 to 2.18]; dominant arm: MD, 0.17 [95% CI, -1.83 to 2.18]). Meta-regression determined that for every 1° increase in shoulder internal rotation (IR), there was a subsequent increase of 0.65° in HT (95% CI, 0.28 to 1.02). HT did not explain external rotation (ER ROM: 0.19 [95% CI, -0.24 to 0.61]) or horizontal adduction (HA ROM: 0.18 [95% CI, -0.46 to 0.82]). There were no differences between HT at the high school, college, or professional levels.

CONCLUSION

No relationship was found between HT and injury risk. However, HT explained 65% of IR ROM but did not explain ER ROM or HA ROM. There were no differences in HT pertaining to competition level. The majority of IR may be nonmodifiable. Treatment to restore and maintain clinical IR may be important, especially in players with naturally greater torsion. HT adaptation may occur prior to high school, which can assist in decisions regarding adolescent baseball participation.

Pediatric Sports Injuries

With increasing pediatric participation in organized sport and the early specialization of children in single sports, the number of injuries seen in the pediatric and adolescent athletic population continues to increase. Children experience acute traumatic injuries during practice and competition as well as chronic overuse injuries secondary to the repetitive stress on their developing bodies. The unique nature of the pediatric patient often requires a different diagnostic, prognostic, and treatment approach to sports injuries compared with their adult counterparts.

Sport Specialization and Increased Injury Frequency in Youth Baseball Players: A Prospective Study

CONTEXT

Sport specialization is thought to be a primary contributor to the throwing-related injury risk in youth baseball players.

OBJECTIVE

To (1) establish arm-injury incidence in a cohort of male youth (9-12 years old) baseball players and (2) examine sport specialization and the frequency of arm injuries in the same cohort.

DESIGN

Cohort study.

SETTING

Greenville, South Carolina, youth baseball programs and tournaments.

PATIENTS OR OTHER PARTICIPANTS

A total of 159 asymptomatic youth baseball players (age = 11.1 ± 1.1 years) were physically assessed and then were prospectively followed for 6.7 ± 1.5 months.

MAIN OUTCOME MEASURE(S)

Athlete demographics and playing and injury histories were initially recorded. Athlete-exposures and presence of arm injury were prospectively tracked. All injuries were physically confirmed by a licensed physical therapist.

RESULTS

Youth players demonstrated an arm-injury incidence rate of 2.22 per 1000 athlete-exposures. Parents and players underestimated sport-specialization status based on the standard research definition (self versus research based: 31% versus 83%, respectively; P = .001). The frequency of arm injuries was higher in specialized players (100%) than in nonspecialized players (80%, P = .03) but did not differ between pitchers and position players (13.2% each, P = 1.00).

CONCLUSIONS

Sport specialization was associated with throwing-related arm injuries in a small cohort of youth baseball players. It is concerning that 57.9% of parents and specialized players were unaware of the athletes' status. Larger studies with longer follow-up periods are needed to further evaluate injury-risk profiles in physically developing youth populations.

The distal radial physis: Exploring normal anatomy on MRI enables interpretation of stress related changes in young gymnasts

Rationale: Explore the MRI-appearance of the healthy distal radial physis and the distribution of stress-related changes in physeal thickness in young gymnasts to aid in the understanding of the pathophysiological process of stress-related physeal injury. Methods: Symptomatic gymnasts with clinically suspected overuse injury of the distal radial physis and age and gender-matched asymptomatic gymnasts and healthy non-gymnasts underwent an MRI-scan of the wrist. A cartilage-specific sequence was used to obtain three-dimensional reconstructions of the distal radial physis. Heat maps and line charts of these reconstructions visualised distribution of physeal thickness per study group and were used to explore differences between study groups. Symptomatic gymnasts displaying the most profound physeal widening (n = 10) were analysed separately. Results: Twenty-seven symptomatic - (skeletal age 12.9 ± 1.5 years), 16 asymptomatic - (skeletal age 12.8 ± 1.9 years) and 23 non-gymnasts (skeletal age 13.6 ± 1.9 years) were included for analysis. Physes of healthy non-gymnasts had a thin centre and increased in thickness towards the borders. Gymnasts demonstrated an increase in thickness of the entire physeal surface. In symptomatic gymnasts increase in physeal thickness was most prominent at the volar side when compared to asymptomatic gymnasts and non-gymnasts. Conclusion: The healthy distal radial physis is characterised by a thin centre surrounded by thicker borders. Stress applied to the wrist during gymnastics causes an overall increase in physeal thickness. Profound thickness increase is present at the volar side of the physis mainly in symptomatic gymnasts. These results can help unravel the pathophysiological mechanism of stress-related physeal injury in gymnasts and aid early injury identification.

Humeral Retroversion and Injury Risk After Proximal Humeral Epiphysiolysis (Little Leaguer's Shoulder)

BACKGROUND

The increased humeral retroversion on the dominant side of throwing athletes is thought to result from repetitive throwing motion. Little Leaguer's shoulder-a rotational stress fracture of the proximal humeral epiphyseal plate-may influence the risk of humeral retroversion and injury of the shoulder or elbow joint.

PURPOSE

To investigate the effect of Little Leaguer's shoulder on humeral retroversion and the rates of shoulder and elbow injuries.

STUDY DESIGN

Cohort study; Level of evidence, 3.

METHODS

10 high school baseball players (average age, 16.6 years; range, 16-18 years) who had experienced Little Leaguer's shoulder during elementary or junior high school (average age, 12.6 years; range, 11-15 years) were enrolled in the study. As a control group, 22 high school baseball players (average age, 16.9 years; range, 16-18 years) who had never had any shoulder or elbow injury during elementary and junior high school were included. Humeral retroversion on ultrasonographic measurement, shoulder range of motion, and rates of shoulder and elbow injuries were evaluated.

RESULTS

Humeral retroversion was significantly greater on the dominant side than on the nondominant side in both players with Little Leaguer's shoulder (dominant, 104°± 8°; nondominant, 84°± 12°; P < .001) and controls (dominant, 91°± 13°; nondominant, 81°± 10°; P < .001). In the dominant shoulder, humeral retroversion was greater in the Little Leaguer's shoulder group than in the control group (P = .008). When the effects of humeral retroversion were excluded, maximal external rotation was significantly less in the dominant shoulder than in the nondominant shoulder in the Little Leaguer's shoulder group (by 11°± 12°, P = .02), whereas no significant difference was found between dominant (110°± 11°) and nondominant (111°± 13°) shoulders in the control group (P = .64). The rates of shoulder and elbow pain were significantly higher in the Little Leaguer's shoulder group (shoulder pain 80%, elbow pain 70%) than in the control group (shoulder pain 9%, P < .001; elbow pain 32%, P = .04).

CONCLUSION

Humeral retroversion was increased in baseball players without any history of shoulder or elbow injury during elementary and junior high school and was further increased in players who had had Little Leaguer's shoulder. Increased humeral retroversion after Little Leaguer's shoulder may be a risk factor for future shoulder or elbow injury.

Rehabilitation and Prehabilitation for Upper Extremity in Throwing Sports: Emphasis on Lacrosse

Lacrosse imposes multiple simultaneous physical demands during play including throwing and catching a ball while holding a crosse, running, cutting, and jumping. Often, these skills are completed while experiencing contact from another player leading to both on-and-off platform movements. Other motions include defensive blocking and pushing past defenders. Repetitive motions over sustained durations in practice or competition impart mechanical stresses to the shoulder or elbow joints, supportive muscles, and connective tissue. Preparation for lacrosse participation involves bilateral optimization of strength and durability of stabilizer muscles. Passing and shooting skills are encouraged to be equally effective on both sides; therefore, symmetric strength and flexibility are vital for prehabilitation and rehabilitation efforts. This article will: 1) provide insights on the upper-extremity musculoskeletal demands of lacrosse and related sports with similar throwing motion and 2) describe prehabilitation and rehabilitation methods that improve athlete durability and reduce likelihood of upper-extremity injury.

Impact of ball weight on medial elbow torque in youth baseball pitchers

HYPOTHESIS

Our hypothesis was that an increase in ball weight would result in an increase in medial elbow torque during the pitching motion.

METHODS

Youth pitchers were recruited for this study and instructed to throw 5 maximum-effort fastballs from ground level using baseballs of 4 different weights: 85 g (3 oz), 113 g (4 oz), 142 g (5 oz), and 170 g (6 oz). The validated Motus sensor was used to assess medial elbow torque, arm speed, arm slot, and shoulder rotation for each pitch. Pitch velocity was measured using a radar gun. Relationships between baseball weight and pitching kinetics and/or kinematics were evaluated using linear mixed-effects analysis. An exit survey was conducted detailing the pitcher's evaluation of the ball weights used.

RESULTS

A total of 19 youth baseball pitchers (average age, 11.8 ± 1.1 years; age range, 9-14 years) completed the study. For every 1-oz (28-g) increase in ball weight, ball velocity decreased 2.0 ± 0.1 mph (χ² = 52.68, P < .001), medial elbow torque increased 0.92 ± 0.37 newton meters (χ² = 5.36, P = .02), and arm speed decreased 8.52 ± 3.68 rpm (χ² = 5.03, P = .02). Shoulder rotation and arm slot were not significantly impacted by ball weight (P > .05). Survey results indicated that the 85-g (3-oz) baseball was most favored (8 of 19 pitchers) and believed to result in the highest pitch velocity (15 of 19 pitchers). The 170-g (6-oz) baseball was least favored (17 of 19 pitchers) and believed to result in the slowest pitch velocity (18 of 19 pitchers). No adverse outcomes were reported with the use of any ball weight or the mobile sensor.

CONCLUSION

Among youth pitchers, an increase in ball weight correlated with greater medial elbow torque, decreased pitch velocity, and decreased arm speed.

Characterization of glenoid bone remodeling in professional baseball pitchers

OBJECTIVE

To characterize the appearance, location, severity, and prevalence of focal glenoid retroversion on shoulder MRI in professional baseball pitchers versus age-matched controls.

MATERIALS AND METHODS

In this retrospective review, two musculoskeletal radiologists evaluated shoulder MRI examinations from 40 professional baseball pitchers and 40 age-matched controls. Images were scored for the presence of a focal posterior glenoid convexity and the clock face positions involved. A consensus interpretation was also performed. A third reader identified the presence of additional shoulder abnormalities.

RESULTS

After consensus, 60% (24/40) of pitchers were found to have focal glenoid retroversion versus 20% (8/40) of controls (p = 0.001). The most apparent location was posterior or posterior-superior, from 7.75 o'clock to 10.5 o'clock (median, 9.75 o'clock; interquartile range, 9.25-10 o'clock). The median clock angle of involvement was greater in pitchers than in controls (30° vs. 0°; p < 0.001). Interreader agreement regarding the presence or absence of focal glenoid retroversion was moderate (Cohen's kappa, 0.49). Focal glenoid retroversion was more prevalent among subjects with additional shoulder abnormalities (p = 0.014).

CONCLUSIONS

Glenoid remodeling occurs in the throwing shoulder of professional baseball pitchers and manifests as focally convex morphology of the posterior or posterior-superior glenoid. This type of remodeling does not appear to be associated with a lower prevalence of injuries related to posterior-superior impingement.

Maturation-dependent findings in the shoulders of pediatric baseball players on magnetic resonance imaging

PURPOSE

To compare the prevalence and characteristics of shoulder osseous and soft tissue findings on magnetic resonance imaging (MRI) with respect to skeletal maturation in symptomatic pediatric baseball players without a history of acute trauma.

METHODS

The IRB-approved, HIPAA-compliant retrospective study analyzed 87 consecutive pediatric baseball players (86 boys and 1 girl; mean age, 15.4 ± 2.1 years) with shoulder MRI performed between March 1, 2012 and September 30, 2017. In consensus, two radiologists assessed the MRI studies for findings involving the humerus, the glenoid, the labrum, the rotator cuff, and the acromioclavicular joint. Exact Cochran-Armitage trend and Mantel-Haenszel Chi-square tests were used to investigate the association between these findings and skeletal maturation.

RESULTS

The mean ages between players who are skeletally immature (37 shoulders), maturing (26 shoulders), and matured (24 shoulders) were significantly different (p < 0.001). Bone marrow edema (p < 0.001) and sclerosis (p < 0.001) within the proximal humeral metaphysis decreased with skeletal maturation. Glenoid remodeling (p = 0.038) was more severe in the skeletally immature players and the prevalence of Bennett lesions (p = 0.048) increased with skeletal maturation. The prevalence of labral tears, rotator cuff tendinosis, and acromioclavicular joint separation did not significantly change with skeletal maturation.

CONCLUSIONS

The change in the prevalence of findings within the proximal humerus and glenoid with skeletal maturation suggest differences in the distribution of stress within the shoulders of pediatric baseball players during development.

Review of Shoulder Range of Motion in the Throwing Athlete: Distinguishing Normal Adaptations from Pathologic Deficits

PURPOSE OF REVIEW

Overhand (OH) throwers demonstrate a unique motion profile of the shoulder joint complex. This manuscript reviews normal adaptations in the OH thrower and contrast findings with pathologic motion deficits.

RECENT FINDINGS

Multiple adaptations in range of motion have been associated with increased risk for arm injury. The use of a more conservative cutoff value for glenohumeral internal rotation deficit and horizontal adduction in younger throwers may help reduce injury risk. Deficits in glenohumeral internal rotation, total range of motion, shoulder flexion, and external rotation insufficiency have all been proposed as means to identify OH throwers at risk for arm injury, but conflicting evidence exists. Understanding normal adaptation due to repetitive stress of throwing is essential to effective management of these athletes. Adaptive change in bone and soft tissues is normal and contributes to the unique motion profiles expected in throwers. The causative link between normal adaptation and shoulder and elbow injury remains uncertain.

The differences of humeral torsion angle and the glenohumeral rotation angles between young right-handed and left-handed pitchers

BACKGROUND

The differences between young right-handed and left-handed baseball players are not well known. This study compared the range of the shoulder motion and humeral torsion angle (HTA) between right-handed and left-handed young baseball pitchers.

METHODS

A total of 65 young baseball pitchers (age, 9-12 years; 46 right-handed throwers, R group; and 19 left-handed throwers, L group) were analyzed. The glenohumeral internal rotation (IR) angle and external rotation (ER) angle were measured at 90° shoulder abduction, and HTA was assessed using indirect ultrasonographic techniques. The side-to-side difference in HTA (d-HTA), glenohumeral ER difference (GERD), and glenohumeral IR deficit (GIRD) were calculated. The adjusted GIRD and adjusted GERD were defined as the angles obtained by subtracting d-HTA from GIRD and GERD, respectively, to exclude the influence of humeral retrotorsion difference.

RESULTS

HTA and ER of the throwing limb were significantly greater than those of the nonthrowing limb in the R group (HTA: 84° vs. 77°; P < .001, ER: 116° vs. 111°; P < .001), but no significant differences were observed in the L group (HTA: 79° vs. 77°, P = .103; ER: 113° vs. 114°, P = .380). Compared with the R group, the L group showed a significantly smaller d-HTA (2° vs. 8°, P < .001) and GERD (5° vs. -2°, P = .004), but no significant difference was observed in adjusted GERD between the groups (-3° vs. -4°, P = .690).

CONCLUSION

Compared with the right-handed pitchers, the side-to-side differences of glenohumeral external rotation angle and humeral torsion angle were significantly smaller in the left-handed pitchers at a young age.