Effect of Anterior Capsular Laxity on Horizontal Abduction and Forceful Internal Impingement in a Cadaveric Model of the Throwing Shoulder

Capsule elongation occurs after first time shoulder dislocation A biomechanical in-vitro investigation on human cadaveric specimen

Purpose

As capsule elongation is assumed to weaken the static stability of the shoulder joint, the purpose of this biomechanical study was to demonstrate that capsule elongation occurs immediately after a first-time shoulder dislocation and not just after recurrent dislocation events. We hypothesize an increment in joint clearance due to joint capsule elongation after a first-time dislocation.

Methods

An experimental in-vitro study was conducted on 6 paired fresh frozen human shoulders (4 females; 2 males; 12 specimen) with a mean age of 80 (Range 67-89) years. The shoulder joint with the articular capsule was exposed and an inferior static tension force of 2.5 N was applied to the humerus prior to dislocation. Next, the humeral head was dislocated and was then immediately reduced back into the start position. The joint gap as well as joint capsule deformation was assessed using optical techniques.

Results

The radiographic joint gap increased from 13.7 ± 6.9 mm (prior to dislocation) to 18.1 ± 6.5 mm (post dislocation) (p < .001). The increase in joint clearance was 4.4 mm. The joint capsule elongated from 5.9 ± 0.005 % (prior to dislocation) to 9.4 ± 0.007 % (post dislocation) (p < .001). The mean increase in joint capsule elongation was 3.5 %.

Conclusions

Capsule elongation was observed immediately after a simulated first-time shoulder dislocation in an in-vitro model of elderly human cadavers. It might therefore not only be a phenomenon of recurrent dislocation events.

Relationships between throwing mechanics and shoulder anterior force in high school and professional baseball pitchers

Background

Excessive shoulder anterior force has been implicated in pathology of the rotator cuff in little league and professional baseball pitchers; in particular, anterior laxity, posterior stiffness, and glenohumeral joint impingement. Distinctly characterized motions associated with excessive shoulder anterior force remain poorly understood.

Methods

High school and professional pitchers were instructed to throw fastballs while being evaluated with 3D motion capture (480 Hz). A supplementary random forest model was designed and implemented to identify the most important features for regressing to shoulder anterior force, with subsequent standardized regression coefficients to quantify directionality.

Results

130 high school pitchers (16.3 ± 1.2 yrs; 179.9 ± 7.7 cm; 74.5 ± 12.0 kg) and 322 professionals (21.9 ± 2.1 yrs; 189.7 ± 5.7 cm; 94.8 ± 9.5 kg) were included. Random forest models determined nearly all the variance for professional pitchers (R2 = 0.96), and less than half for high school pitchers (R2 = 0.41). Important predictors of shoulder anterior force in high school pitchers included: trunk flexion at maximum shoulder external rotation (MER) (X.IncMSE = 2.4, β = -0.23, p < 0.001), shoulder external rotation at ball release (BR)(X.IncMSE = 1.7, β = -0.34, p < 0.001), and shoulder abduction at BR (X.IncMSE = 3.1, β = 0.17, p < 0.001). In professional pitchers, shoulder horizontal adduction at foot contact (FC) was the highest predictor (X.IncMSE = 13.9, β = 0.50, p < 0.001), followed by shoulder external rotation at FC (X.IncMSE = 3.6, β = 0.26, p < 0.001), and maximum elbow extension velocity (X.IncMSE = 8.5, β = 0.19, p < 0.001).

Conclusion

A random forest model successfully selected a subset of features that accounted for the majority of variance in shoulder anterior force for professional pitchers; however, less than half of the variance was accounted for in high school pitchers. Temporal and kinematic movements at the shoulder were prominent predictors of shoulder anterior force for both groups.

Clinical relevance

: Our statistical model successfully identified a combination of features with the ability to adequately explain the majority of variance in anterior shoulder force among high school and professional pitchers. To minimize shoulder anterior force, high school pitchers should emphasize decreased shoulder abduction at BR, while professionals can decrease shoulder horizontal adduction at FC.

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.

Is Workload Associated With Internal Impingement in Professional Baseball Pitchers? An Analysis of Days of Rest, Innings Pitched, and Batters Faced

Background

Internal impingement is a common cause of shoulder pain and dysfunction in baseball pitchers.

Purpose/Hypothesis

The purpose of this study was to determine if the amount of rest days between outings, the number of innings pitched in each outing, and the number of batters faced in each outing are risk factors for internal impingement in professional baseball pitchers. It was hypothesized that a higher workload would significantly increase a pitcher's risk of developing internal impingement.

Study Design

Case-control study; Level of evidence, 3.

Methods

All professional (Major and Minor League) baseball pitchers who were diagnosed with internal impingement between 2011 and 2017 were identified using the Major League Baseball's Health and Injury Tracking System. A separate player usage data set was used to determine workload. The authors compared workload variables (days of rest, innings pitched, and batters faced per game) between each of 4 injury-exposure groups (pitchers with documented internal impingement <2, <6, <12, and >12 weeks after a game) and a control group of pitchers with no internal impingement using Student t tests or Mann-Whitney U tests. In a within-pitcher paired analysis of the injury groups, the workload variables during 3 acute periods (<2, <6, and <12 weeks preinjury) were compared with the baseline values (>12 weeks preinjury).

Results

Overall, there were 624 professional baseball pitchers diagnosed with internal impingement during the study period. Compared with pitcher games (n = 213,964), pitchers in all 4 injury-exposure groups had significantly more innings pitched per game (P ≤ .003 for all) and faced significantly more batters per game (P < .001 for all). There were significantly more starting pitchers in each of the injury-exposure groups when compared with the controls (P < .001 for all). However, when comparing acute and baseline workloads in the pitchers diagnosed with internal impingement, there were no significant differences in the number of innings pitched, batters faced, or days of rest.

Conclusion

This analysis revealed significantly greater pitcher workload and percentage of starting pitchers in professional baseball players diagnosed with internal impingement when compared with healthy controls. However, this injury did not seem to be associated with an acute increase in workload.

The relationship between scapular position and glenohumeral rotational range of motion in high school baseball players

BACKGROUND

Past research indicated that scapular malposition is related to the glenohumeral internal rotation deficit (GIRD). However, there is no research examining the effect of throwing-related pain on this relationship. This study investigated the relationship between scapular position and range of motion (ROM) and compared the difference in this relationship between with and without throwing-related pain.

METHODS

Forty male baseball players in high school were recruited for this study. The existence and degree of throwing-related pain were obtained from a questionnaire. Participants were divided into 2 groups according to the presence or absence of the pain. Glenohumeral internal and external rotation ROM (abduction internal rotation angle and abduction external rotation angle [ABER], respectively) were measured using a digital inclinometer. The pectoralis minor muscle length was measured using a vernier caliper and scapula index, which indicated the scapular position, measured using a measuring tape. All these measurements were taken on both dominant and nondominant sides. The GIRD and total motion arc (TMA) deficit were calculated from the ROM measurements. Groups were compared using a mixed-model analysis of variance.

RESULTS

There was a significant interaction between group and ABER dominance. Other variables were not seen as the interaction effect. There was a significant positive correlation between the scapula index and TMA (r = 0.47, P = .02) and a negative correlation between the scapula index and GIRD (r = -0.65, P < .01) in the dominant side of the pain group. In addition, in the nondominant side of the pain group, the scapula index and ABER were significantly correlated (r = 0.43, P = .04).

CONCLUSIONS

The results of this study indicate that the scapular position is associated with the glenohumeral ROM in high school baseball players. In addition, this study demonstrated that the scapular internally rotated position was correlated with the GIRD and TMA deficit in high school baseball players who had throwing-related pain. On the other hand, the scapular externally rotated position was correlated with increased ABER, mainly in the pain-free baseball players or on the nondominant side. These results indicated that the scapular position might affect the glenohumeral rotational ROM in high school baseball players.

Increased external rotation related to the soft tissues is associated with pathologic internal impingement in high-school baseball players

BACKGROUND

Changes in soft-tissue structures such as anterior laxity and posterior tightness are thought to contribute to the development of pathologic internal impingement in baseball players. Although side-to-side differences in shoulder rotational range of motion (ROM) is commonly used in clinical practice to quantify the soft-tissue changes, the ROM does not accurately reflect the soft-tissue changes because the ROM is affected not only by the soft tissues, but also by the bone. Increased retroversion of the humeral head is often observed in the dominant shoulder of throwing athletes. The purpose of this study was to determine the relationship between the soft-tissue-related (STR) ROM and pathologic internal impingement in baseball players.

METHODS

Bilateral humeral retroversion and ranges of glenohumeral external rotation (ER) and internal rotation (IR) were investigated in 81 high-school baseball players. The players were divided into two groups: the internal impingement group (19 players) and the control group (62 players). Humeral retroversion was measured using the ultrasound-assisted technique to assess the bone-related ER and IR. The STR ER and IR were defined as subtracting the amount of humeral retroversion from the measured ER and IR.

RESULTS

The side-to-side difference (throwing shoulder - nonthrowing shoulder) in humeral retroversion showed no significant difference between the internal impingement group (6° ± 10°) and control group (11° ± 11°) (P = .064). The side-to-side difference in STR ER was significantly greater in the internal impingement group (12° ± 12°) than that in the control group (1° ± 14°) (P = .002). No significant difference was observed in the side-to-side difference in STR IR between the internal impingement group (-7° ± 16°) and control group (-5° ± 15°) (P = .696). Pathologic internal impingement was significantly associated with the side-to-side difference of STR ER (odds ratio, 1.06 for increase of 1°; 95% confidence interval, 1.02-1.11; P = .008).

CONCLUSION

In high-school baseball players, the increased STR ER in the throwing shoulder may be associated with pathologic internal impingement. An increase of 10° in side-to-side difference in STR ER would increase the risk of pathologic internal impingement by 1.8 times.

Anterior glenohumeral capsular ligament reconstruction with hamstring autograft for internal impingement with anterior instability of the shoulder in baseball players: preliminary surgical outcomes

BACKGROUND

Shoulder pain and dysfunction are common in baseball players, and although "internal impingement" is recognized as one of the most common pathologies of shoulder dysfunction, the optimal surgical treatment for internal impingement with anterior instability of the shoulder remains controversial. This study evaluated baseball players' preliminary outcomes following anterior glenohumeral capsular ligament reconstruction for internal impingement with anterior instability of the shoulder.

METHODS

Twelve baseball players (all male; mean age, 20.5 ± 2.2 years) with internal impingement and anterior instability managed via anterior glenohumeral capsular ligament reconstruction were examined. The mean follow-up period was 25.3 ± 4.6 months. Anterior glenohumeral capsular ligament reconstruction was performed with a knee hamstring autograft for balanced stability and laxity with two major targets: to prevent hyperangulation and translation in horizontal abduction and to mimic the individual arm cocking position at the final decision of tension. Preoperative and final follow-up evaluations were performed using Jobe's postoperative grading system; the Kerlan-Jobe Orthopaedic Clinic Overhead Athletes Shoulder and Elbow Score; Disabilities of the Arm, Shoulder and Hand sports module; plain radiographs; and magnetic resonance imaging.

RESULTS

Jobe's postoperative grading system score, the Kerlan-Jobe Orthopaedic Clinic Overhead Athletes Shoulder and Elbow Score, and the Disabilities of the Arm, Shoulder and Hand sports module score improved significantly from 20.4 ± 12.2, 28.4 ± 8.3, and 80.2 ± 11.1 points preoperatively to 88.8 ± 13.6, 80.8 ± 7.7, and 22.4 ± 18.7 points postoperatively, respectively (P < .001, .0025, <0.001, respectively). Both clinical and imaging evaluations revealed improved internal impingement with anterior instability after anterior glenohumeral capsular ligament reconstruction. The mean external rotation at abduction significantly decreased from 113° preoperatively to 104° postoperatively. At follow-up, 10 of the 12 athletes (83.3%) returned to their prior competitive level. Plain radiographs and magnetic resonance imaging revealed no obvious loosening of the graft or screws.

CONCLUSIONS

Anterior glenohumeral capsular ligament reconstruction resulted in preferable clinical outcomes for young baseball players who experienced pain during the throwing motion. Stabilization of the glenohumeral joint with autografting of the knee hamstring may thus represent a solution for internal impingement with anterior instability in overhead throwing athletes.

Supraspinatus Tendon Changes and Glenohumeral Range of Motion in College Baseball Players

Baseball players commonly show altered glenohumeral range of motion during internal rotation, external rotation, total rotation, and horizontal adduction. These altered ranges of motion appear to be associated with throwing shoulder injuries, which frequently involve the supraspinatus tendons; thus, we aimed to examine the relationship between altered glenohumeral range of motion and supraspinatus tendon changes in collegiate baseball players. To investigate this association using the Pearson correlation coefficient, we measured glenohumeral internal rotation, external rotation, total rotation, and horizontal adduction ranges of motion and supraspinatus tendon thickness in 22 college baseball players. Consequently, there was a significant relationship between increase in supraspinatus tendon thickness and greater deficit of internal rotation (r=-0.520, P=0.013). Increased supraspinatus tendon thickness tended to be associated with greater external rotation gain (r=0.394, P=0.073). No other range of motion had any relationship with supraspinatus tendon changes. These results might indicate that restricted glenohumeral internal rotation and excessive gain in external rotation increase the risk of supraspinatus tendon abnormalities in baseball players.

Management Options for Shoulder Impingement Syndrome in Athletes: Insights and Future Directions

Athletes participating in overhead sports are at particularly high risk of shoulder impingement syndrome. Subcoracoid impingement is defined as impingement of the anterior soft tissues of the shoulder between the coracoid process and the lesser tuberosity. Subacromial impingement syndrome (SIS) occurs due to extrinsic compression of the rotator cuff between the humeral head and coracoacromial structures or intrinsic degeneration of the supraspinatus tendon and subsequent superior migration of the humerus. Internal impingement is a major cause of shoulder pain in overhead athletes, and it occurs due to repetitive impingement of the articular surface of the rotator cuff with the glenoid during maximum abduction and external rotation of the arm. When examining athletes with suspected impingement of the shoulder, it is important to discuss the sport-specific motion that regenerates the symptoms and perform a combination of physical examination tests to improve the diagnostic accuracy. Radiographic evaluation is recommended, and the extent of soft tissue abnormalities can be assessed on ultrasound or magnetic resonance imaging of the shoulder. Management of shoulder impingement syndrome can be conservative or operative, based on the severity and chronicity of symptoms and the associated structural abnormalities. This review provides an update on the management of SIS, subcoracoid impingement, and internal impingement in the athletic population.

The cricketer's shoulder and injury: Asymmetries in range of movement and muscle length

Background

Shoulder injuries in cricket are often undetected and untreated.

Objectives

To determine whether there are associations between shoulder internal and external rotation range of movement (ROM), throwing arc (TA) ROM, glenohumeral internal rotation deficit (GIRD), external rotation gain (ERG), pectoralis minor muscle length and the incidence of shoulder injury during the first 3 months of a cricket season amongst provincial and club cricketers.

Method

Male, actively participating, provincial and club cricketers were included in this prospective longitudinal cohort study. The independent variables included shoulder pain, which did not limit participation in cricket training and matches; shoulder external and internal rotation (ROM, TA ROM, GIRD and ERG) and pectoralis minor muscle length. Time-loss dominant shoulder injury was recorded for 3 months.

Results

Nine of the 32 participants sustained dominant shoulder injuries. Initial non-time-loss shoulder pain during baseline testing was associated with time-loss in-season shoulder injury (p = 0.007). Statistically significant side-to-side differences were found for all of the independent variables (internal rotation ROM, TA ROM and pectoralis minor muscle length distance), with the exception of external rotation ROM, amongst the uninjured players.

Conclusion

Non-time-loss-defined shoulder pain in actively participating cricketers seems to be a precursor to time-loss shoulder injury. Asymmetries in ROM and pectoralis minor muscle length in uninjured cricketers may have a protective role to play in the case of shoulder injury.

Clinical implications

The presence of shoulder pain and asymmetries in ROM should be investigated during the pre-season screening procedures, and early intervention should be implemented where appropriate.

Partial-Thickness Rotator Cuff Tear by Itself Does Not Cause Shoulder Pain or Muscle Weakness in Baseball Players

BACKGROUND

Partial-thickness rotator cuff tears are common shoulder injuries in baseball players. For some tears, the symptoms can be relieved through physical therapy or debridement without rotator cuff repair.

PURPOSE

To assess whether partial-thickness rotator cuff tear by itself causes shoulder pain and muscle weakness in baseball players.

STUDY DESIGN

Cross-sectional study; Level of evidence, 3.

METHODS

We studied 87 university baseball players (age, 19.5 ± 0.8 years; baseball career, 11.5 ± 1.6 years). All data were obtained during a full-participation annual medical check in 1 team. Rotator cuff tendons were examined ultrasonographically and allocated to 4 groups: (1) no tear, (2) supraspinatus tendon tear, (3) infraspinatus tendon tear, and (4) both supraspinatus and infraspinatus tendon tears. Current shoulder pain and shoulder muscle strength (dominant/nondominant) in abduction, external rotation, and internal rotation were compared by using chi-square and t tests. All players could play baseball with or without shoulder pain in this study.

RESULTS

Of the 87 players, 41 (47%) had articular-sided partial-thickness rotator cuff tears diagnosed on ultrasonography; the remaining 46 athletes were tear-free. Of the 41 affected patients, 19 had tears in the supraspinatus, 13 in the infraspinatus, and 9 in both the supraspinatus and infraspinatus tendons. Tear depth (mean ± SD) was 4.6 ± 2.3 mm in the supraspinatus and 6.2 ± 3.6 mm in the infraspinatus. Neither the rate of shoulder pain nor muscle strength differed significantly among the 4 groups (P = .96 and P = .15-.70, respectively).

CONCLUSION

Articular-sided partial-thickness rotator cuff tear-by itself-did not cause shoulder pain and muscle weakness in university baseball players. Most so-called articular-sided partial-thickness rotator cuff tears may not be pathologic tendon tears.

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.

Estimation of Shoulder Behavior From the Viewpoint of Minimized Shoulder Joint Load Among Adolescent Baseball Pitchers

BACKGROUND

During pitching, an overloaded joint reaction force exerted on the shoulder and excessive shoulder horizontal abduction at ball release are considered risk factors causing anterior shoulder pain for young baseball pitchers. Hypothesis/Purpose: The first aim was to examine the relationship between shoulder horizontal abduction position and force on the shoulder at ball release. The second was to identify the relative rotational position of the shoulder and the range of shoulder motion at ball release that minimize force on the shoulder. It was hypothesized that the amount of force on the shoulder would be exacerbated by excessive shoulder horizontal abduction.

STUDY DESIGN

Descriptive laboratory study.

METHODS

Participants were 183 adolescent baseball pitchers (mean ± SD age, 15.5 ± 1.2 years) without shoulder/elbow problems. Each pitcher threw 5 fastballs to a catcher behind a home plate. The kinematics and kinetics of the throwing shoulder during fastball pitching were calculated with 3-dimensional measurements from 36 reflective markers. In data analysis, the correlations were calculated between the relative rotational positions of the shoulder (abduction, horizontal adduction-abduction) and the forces on the shoulder (anterior-posterior, proximal, and superior-inferior) at ball release. Subsequently, the specific rotational position and range of motion of the shoulder at ball release that minimized forces on the shoulder were determined.

RESULTS

Statistically significant correlations were identified between the magnitude of superior-inferior force on the shoulder and shoulder abduction position ( R² = 0.44, P < .001) as well as between the magnitude of anterior-posterior force on the shoulder and shoulder horizontal adduction-abduction position ( R² = 0.72, P < .001). Minimal anterior-posterior and superior-inferior forces were obtained with a combination of 80.6° of shoulder abduction and 10.7° of shoulder horizontal adduction. Any deviation >5° from this position significantly increased the anterior-posterior and superior-inferior forces on the shoulder.

CONCLUSION

Increasing shoulder horizontal abduction position significantly increased the magnitude of anterior force on the shoulder at ball release. The combination of 80.6° of shoulder abduction and 10.7° of horizontal shoulder adduction minimized the shear forces on the shoulder at this point.

CLINICAL RELEVANCE

The present data can be useful for screening pitching technique to prevent shoulder pain and injury with motion capture assessment.

Lower shoulder abduction during throwing motion may cause forceful internal impingement and decreased anterior stability

BACKGROUND

Internal impingement and decreased anterior stability, which result from shoulder capsular loosening, are common shoulder pathologies in throwing athletes. The purpose of this study was to assess the effect of shoulder abduction angle on shoulder internal impingement and anterior shoulder stability during the simulated throwing motion.

METHODS

Eight cadaveric shoulders were tested by simulating the late-cocking and acceleration phases of the throwing motion for intact and thrower's shoulder conditions. The maximal glenohumeral external rotation, anterior translation, location of the rotator cuff insertion with respect to the glenoid, length and site of internal impingement, and glenohumeral contact pressure were measured. All data were compared between shoulder abduction angles of 80°, 90°, and 100°.

RESULTS

Decreasing shoulder abduction in the simulated late-cocking phase shifted the humeral head posteriorly (P < .03) and superiorly (P < .001), decreasing the total internal impingement area between the greater tuberosity and glenoid (P = .04) and increasing the glenohumeral contact pressure during internal impingement (P = .02). In the simulated acceleration phase, anterior glenohumeral translation significantly increased as the shoulder abduction angle decreased (P < .001).

CONCLUSION

Decreasing shoulder abduction significantly increased the contact pressure during internal impingement in the simulated late-cocking phase of the throwing motion. During the simulated acceleration phase of the throwing motion, anterior glenohumeral translation significantly increased as shoulder abduction decreased.

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.

Pathologies of the shoulder and elbow affecting the overhead throwing athlete

The overhead-throwing athlete is susceptible to a variety of predictable disease entities affecting the shoulder and elbow. While the pathophysiology and nomenclature of these diseases are ubiquitous throughout the clinical literature, this information is sparse within the radiology domain. We provide a comprehensive review of these unique injuries with accompanying imaging features in an effort to enhance the role of the radiologist during the management of the overhead thrower. When appropriately recognized and described, the imaging features aid in establishing a diagnosis and ultimately the implementation of appropriate clinical management.

Relationship Between Humeral Retroversion and Length of Baseball Career Before the Age of 16 Years

BACKGROUND

Humeral retroversion physiologically decreases during growth. However, in throwing athletes, the external forces caused by repetitive throwing are thought to increase humeral retroversion on the dominant side compared with that on the nondominant side.

PURPOSE

To investigate the correlation between humeral retroversion and length of baseball career before age 16 years.

STUDY DESIGN

Cross-sectional study; Level of evidence, 3.

METHODS

A total of 112 high school baseball players (32 pitchers and 80 position players) with a mean age of 15.6 years (range, 15-16 years) were enrolled in the study. All participants completed questionnaires regarding their player position and the age when they started baseball and were given physical examinations. Shoulder range of motion and humeral retroversion were assessed on the dominant and nondominant sides. Humeral retroversion (rotation angle of the proximal humerus relative to the distal humerus) was measured ultrasonographically.

RESULTS

Humeral retroversion was significantly greater on the dominant side than on the nondominant side in both pitchers (P < .0001) and position players (P = .0005). The side-to-side difference in humeral retroversion in pitchers (13.9° ± 11.2°) was significantly greater than that in position players (9.0° ± 11.1°, P = .0361). In pitchers, there was a significant negative correlation between humeral retroversion and the age at which the players had started baseball (P = .033, β = -2.494).

CONCLUSION

These results suggest that humeral retroversion increases with decreasing age at commencement of a baseball career before age 16 years in pitchers.

[Surgical treatment of posterosuperior impingement (PSI)]

OBJECTIVE

To restore the physiologic anterior and posterior capsular volume to achieve an anatomic central contact point of the glenohumeral articulation and treatment of concomitant glenohumeral injuries due to posterosuperior impingement (PSI).

INDICATIONS

Plateauing of clinical improvement despite adequate nonsurgical treatment (for at least 6-12 months).

CONTRAINDICATIONS

General contraindications for elective arthroscopic surgery.

SURGICAL TECHNIQUE

Diagnostic arthroscopy of the glenohumeral joint through the posterior portal to assess stability of the biceps-labral complex even in the Abduction and External Rotation (ABER) position to confirm the diagnosis of PSI and to detect concomitant glenohumeral injuries. In most cases posterosuperior SLAP (superior labrum anterior posterior) repair or tenodesis of the long head of the biceps.

POSTOPERATIVE MANAGEMENT

Arm sling for 6 weeks with limited range of motion. Free active range of motion of elbow and wrist. Limited shoulder external rotation for 6 weeks. Free shoulder range of motion from week 7, full daily life activities after 12 weeks. Modification of the postoperative management according to intraoperative findings.

RESULTS

At our hospital 18 overhead athletes (6 women, 12 men, mean age 31 years) with PSI without SLAP lesion or rotator cuff tear underwent isolated plication of the anteroinferior capsule after primary nonsurgical treatment. At a mean period of 9 months, 16 patients returned to their pre-injury sports activity level, 2 patients had to give up their sports due to persisting shoulder problems. At a mean follow-up of 27 months (range 12-55 months) the Walch Duplay score was on average 82.9 ± 8.3 for men and 73.8 ± 5.9 for women.