Burkhart, Morgan & Kibler (2003) The disabled throwing shoulder: spectrum of pathology Part I: pathoanatomy and biomechanics

Several years ago, when we began to question microinstability as the universal cause of the disabled throwing shoulder, we knew that we were questioning a sacrosanct tenet of American sports medicine. However, we were comfortable in our skepticism because we were relying on arthroscopic insights, clinical observations, and biomechanical data, thereby challenging unverified opinion with science. In so doing, we assembled a unified concept of the disabled throwing shoulder that encompassed biomechanics, pathoanatomy, kinetic chain considerations, surgical treatment, and rehabilitation. In developing this unified concept, we rejected much of the conventional wisdom of microinstability-based treatment in favor of more successful techniques (as judged by comparative outcomes) that were based on sound biomechanical concepts that had been scientifically verified. Although we have reported various components of this unified concept previously, we have been urged by many of our colleagues to publish this information together in a single reference for easy access by orthopaedic surgeons who treat overhead athletes. We are grateful to the editors ofArthroscopy for allowing us to present our view of the disabled throwing shoulder. Part I: Patho- anatomy and Biomechanics is presented in this issue. Part II: Evaluation and Treatment of SLAP Lesions in Throwers will be presented in the May-June issue. Part III: The “SICK” Scapula, Scapular Dyskinesis, the Kinetic Chain, and Rehabilitation will be presented in the July-August issue. We hope you find it thought-provoking and compelling.

Burkhart, Morgan & Kibler (2003) The disabled throwing shoulder: spectrum of pathology part II: evaluation and treatment of SLAP lesions in throwers

As we stated in Part I, Pathoanatomy and Biome- chanics in the April issue of the Journal, the pathologic cascade that leads to production of a SLAP lesion is devastating to the overhead athlete. Once the SLAP lesion is produced, the thrower can no longer perform. It is imperative that the orthopaedic surgeon be able to accurately diagnose and adequately treat this pathologic lesion, which we believe is the most common cause of the dead arm.

Andersson, Bahr, Clarsen & Myklebust (2017) Preventing overuse shoulder injuries among throwing athletes: a cluster-randomised controlled trial in 660 elite handball player

Objective To evaluate the effect of a comprehensive exercise program designed to reduce the prevalence of shoulder problems in elite handball.
Design Stratified cluster-randomised controlled trial with teams as the unit of randomisation
Setting 45 handball teams (22 female, 23 male) from the two upper divisions in Norway (22 in the intervention group, 23 in the control group) were followed for one competitive season (7 months).
Participants 660 players aged 16-47 (331 in the intervention group, 329 in the control group).
Intervention Ten-minute comprehensive exercise program to increase glenohumeral internal rotation, external rotation strength and scapular control, as well as improve kinetic chain and thoracic mobility, to be delivered by coaches and team captains three times per week as a part of the handball warm-up throughout the season.
Main outcome measures Prevalence of shoulder problems and substantial shoulder problems.
Results The average prevalence of shoulder problems during the season was 17% (95% CI: 16% to 19%) in the intervention group and 23% (95% CI: 21% to 26%) in the control group (mean difference: 6%). The average prevalence of substantial shoulder problems was 5% (95% CI: 4% to 6%) in the intervention group and 8% (95% CI: 7% to 9%) in the control group (mean difference: 3%). Using generalized estimating equation models, a 28% lower risk of shoulder problems (OR 0.72, 95% CI: 0.52 to 0.98, p=0.038) and 22% lower risk of substantial shoulder problems (OR 0.78, 95% CI: 0.53 to 1.16, p=0.23) was observed in the intervention group compared to the control group.
Conclusion A comprehensive exercise program reduced the prevalence of shoulder problems in elite handball.

Burkhart & Lo (2007) The cam effect of the proximal humerus: its role in the production of relative capsular redundancy of the shoulder

Purpose The purpose of this study was to investigate quantitatively the cam effect of the proximal humerus whereby the anteroinferior capsule of the shoulder is tensioned in abduction–external rotation by virtue of asymmetric rotation of the eccentrically positioned humeral head), as well the extent to which a reduction in the cam effect would cause a relative capsular redundancy, in the cadaveric shoulder. 
Methods Five fresh-frozen cadaveric shoulders were tested. K-wires were used to sequentially position the shoulder in 3 different positions: neutral anatomic position, with contact at the glenoid bare spot; 90°-90° neutral shift position, with contact at the glenoid bare spot; and 90°-90° posterosuperior shift position, with contact 4.3 mm posterosuperior to the glenoid bare spot. The topographic anterior band distance (TABD) was measured with the shoulder in each of the 3 positions. The relative redundancy that occurred by shifting the glenohumeral contact point was determined by subtracting the TABD in the 90°-90° posterosuperior shift position from the TABD in the 90°-90° neutral shift position.
Results The results of repeated-measures analysis of variance showed significant differences among the mean TABD values for the 3 positions (P < .010). There was a significant increase in TABD when the shoulder was brought from the neutral anatomic position to the 90°-90° neutral shift position (P < .020), confirming the cam effect of the proximal humerus in the 90°-90° position. Furthermore, the TABD decreased significantly when the 90°-90° neutral shift position changed to the 90°-90° posterosuperior shift position (P < .005), indicating a significant reduction in the cam effect with a concomitant relative redundancy in the anteroinferior capsuloligamentous complex.
Conclusions The proximal humerus produces a significant cam effect on the anteroinferior capsule when the shoulder is brought into a position of 90° abduction and 90° external rotation. A reduction in the cam effect as a result of a posterosuperior shift of the glenohumeral contact point with the shoulder in the 90°-90° position results in a relative redundancy of the anteroinferior capsuloligamentous complex. This relative capsular redundancy, coupled with the pseudolaxity that occurs with SLAP lesions, can produce a degree of apparent anterior laxity that is independent of any true translational anterior instability.
Clinical Relevance The relative redundancy in the anteroinferior shoulder capsule caused by a decrease in the cam effect of the proximal humerus may have clinical implications in the pathophysiology of the disabled throwing shoulder. This relative redundancy is a secondary pseudolaxity, with the primary pathology being a tight posteroinferior capsule. Appropriate treatment (stretching of the posteroinferior capsule) of the primary pathology is a more appropriate initial treatment than instability surgery.

Tristan Chai