Abstract
Background: The quantitative relationship between increased anterior shoulder laxity and increased humeral external rotation observed in throwers remains unclear. Hypothesis: An elongated anterior capsule, especially the anterior band of the inferior glenohumeral ligament, produced by excessive humeral external rotation will result in increased anterior shoulder laxity and increased humeral external rotation. Study Design: Controlled laboratory study. Methods: Seven cadaveric shoulders were tested to measure the humeral rotational range of motion, glenohumeral translations, and length of the anterior band of the inferior glenohumeral ligament. Data were collected for the intact shoulders and after non-destructive stretching of 10%, 20%, and 30% beyond maximum humeral external rotation. Results. Nondestructive excessive external rotational stretching resulted in a significant increase in superior (30%, 3.3 mm) and inferior (30%, 2.3 mm) length of the anterior band of the inferior glenohumeral ligament, external rotation (30%, 35°), and anterior (30%, 2.4 mm), inferior (30%, 2.2 mm), and anterior-posterior (30%, 5.1 mm) translations. There were significant positive linear correlations between the length of the anterior band of the inferior glenohumeral ligament, external rotation, and anterior translation. Conclusions: Excessive humeral external rotation results in an elongation of the anterior band of the inferior glenohumeral ligament and an increase in anterior and inferior glenohumeral translations and humeral external rotation. Clinical Relevance: Repetitive excessive humeral external rotation observed in throwers may be one of the biomechanical causes for increased shoulder laxity and increased humeral external rotation.