Humeral head retroversion in competitive baseball players and its relationship to glenohumeral rotation range of motion

Imaging shoulder instability in the athlete

Athletes who partake in overhead or throwing activities frequently suffer from shoulder pain. Glenohumeral instability plays an important role in sports-related shoulder pain. Shoulder instability can be traumatic, atraumatic, or microtraumatic in origin. In athletes, atraumatic and microtraumatic instabilities can lead to secondary impingement and chronic damage to intra-articular structures. MR arthrography is the modality of choice for assessing glenohumeral instability and diagnosing labroligamentous injuries. This article reviews imaging of instability-related injuries in athletes, with special emphasis on MR imaging.

Throwing induces substantial torsional adaptation within the midshaft humerus of male baseball players

Athletes participating in unilateral dominant sports are useful models for investigating skeletal responses to mechanical loading as they provide controlled evidence in the absence of completing a randomized controlled trial. Throwing athletes may be an additional model for this purpose as they overload their dominant upper extremity enabling the contralateral side to act as an internal control and load the bones of the upper extremity purely via the generation of internal (i.e. muscular) forces without superposition of externally applied loads (i.e. impact with an external object). The aim of this study was to investigate upper extremity bone adaptation in throwing athletes and explore factors that predict this adaptation. Two cohorts were recruited-male baseball players (throwers; n=15) and matched controls (controls; n=15). Each subject was assessed for shoulder range and strength, and upper extremity bone mass, structure and estimated strength. Throwers had substantially greater skeletal differences between their dominant and nondominant upper extremities than controls, indicating that throwing induces greater adaptation than induced by habitual loading of the dominant upper extremity. Bone adaptation in throwers was localized to the humerus, with the midshaft humerus in the dominant upper extremity of throwers having enhanced bone mass, structure and estimated strength. The largest effect was for estimated strength of the midshaft humerus which had 30% greater polar moment of inertia (I(P)) in throwers and suggests adaptation to resist torsional loads. The skeletal effect of throwing at the midshaft humerus was influenced by playing position with pitchers and catchers displaying greater dominant-to-nondominant differences than fielders, and was predicted by years throwing and dominant-to-nondominant difference in upper arm lean cross-sectional area. The latter two variables explained 67% of the variance in dominant-to-nondominant differences in I(P). Collectively, these data indicate that throwing induces substantial adaptation within the midshaft humerus. Adaptation was primarily in the direction of torsion which is consistent with biomechanical and injury data suggesting throwing introduces high magnitude torsional forces. As the magnitude of adaptation in throwers was equivalent to that observed in athletes participating in other unilateral dominant sports, throwers represent an alternative model for investigating the skeletal effects of mechanical loading.

Sports participation and humeral torsion

STUDY DESIGN

Cross-sectional study.

OBJECTIVE

To examine differences between arms in humeral torsion in adult and adolescent throwing and nonthrowing athletes, and nonathletic adults.

BACKGROUND

It is hypothesized that humeral retrotorsion develops by, and is beneficial for, throwing. Thus throwers should demonstrate greater retrotorsion in their dominant arm relative to their nondominant arm and have more side-to-side retrotorsion difference than nonthrowing groups. In addition, adult throwers should have a greater side-to-side retrotorsion difference than adolescent throwers, and swimmers should not demonstrate a retrotorsion difference.

METHODS AND MEASURES

Using ultrasound to standardize the location of the bicipital groove, the amount of humeral torsion was measured in both arms of male baseball players (85 adult, 35 adolescent), female softball players (16 adult, 37 adolescent), 29 elite adolescent swimmers (19 female), and 16 nonathletic adults (8 female).

RESULTS

More retrotorsion was found in the dominant arm of almost all throwing athletes, irrespective of their gender or whether they were adults or adolescents (mean+/-SD side-to-side difference, 11.9 degrees+/-10.5 degrees). This difference was less for swimmers (6.4 degrees+/-9.9 degrees) and nonathletic adults (1.3 degrees+/-8.9 degrees).

CONCLUSION

Greater dominant armhumeral retrotorsion is observed contingent with participation in throwing sports.

Shoulder injuries in the overhead athlete

The overhead throwing motion is an extremely skillful and intricate movement. When pitching, the overhead throwing athlete places extraordinary demands on the shoulder complex subsequent to the tremendous forces that are generated. The thrower's shoulder must be lax enough to allow excessive external rotation but stable enough to prevent symptomatic humeral head subluxations, thus requiring a delicate balance between mobility and functional stability. We refer to this as the "thrower's paradox." This balance is frequently compromised and believed to lead to various types of injuries to the surrounding tissues. Frequently, injuries can be successfully treated with a well-structured and carefully implemented nonoperative rehabilitation program. The key to successful nonoperative treatment is a thorough clinical examination and accurate diagnosis. Rehabilitation follows a structured, multiphase approach, with emphasis on controlling inflammation, restoring muscles' balance, improving soft tissue flexibility, enhancing proprioception and neuromuscular control, and efficiently returning the athlete to competitive throwing. Athletes often exhibit numerous adaptive changes that develop from the repetitive microtraumatic stresses occurring during overhead throwing. Treatment should include the restoration of these adaptations.

LEVEL OF EVIDENCE

Level 5.

Humeral torsion and passive shoulder range in elite volleyball players

OBJECTIVES

To evaluate variations in humeral torsion in elite male volleyball players and determine whether these changes are related to training history, retrospective injury history and volleyball performance.

DESIGN AND SETTING

Cross sectional design.

PARTICIPANTS

Twenty-four elite male volleyball players.

MAIN OUTCOME MEASURES

Humeral torsion, passive gleno-humeral rotation ranges and the available internal and external rotation from the humeral torsion neutral position of the dominant and non-dominant arm were measured. Training history and retrospective injury status were ascertained from a questionnaire. Performance was assessed by coach perceived spiking ability and peak serve velocity measures.

RESULTS

Humeral torsion angles demonstrated the dominant arm to be on average 9.6 degrees more retroverted than the non-dominant arm (p=0.00). In the comparison of volleyball players with and without a history of overuse upper limb injury the most significant finding is on the non-dominant side, those with a history of injury had significantly decreased available external rotation from the humeral torsion neutral position (mean difference=-15.1, p=0.04). There was an unexpected negative weak relationship between age commenced and decreased humeral retroversion (r=-0.413, p=0.045). There did not appear to be any relationship between humeral torsion and performance measures.

CONCLUSION

The dominant arm of elite male volleyball athletes is more retroverted. There was a tendency for stronger findings in the non-dominant arm in volleyball players with retrospective injury history. We were unable to find any significant correlation between humeral torsion angle and performance measures.