Subcoracoid impingement, while relatively uncommon in clinical incidence when compared to subacromial impingement, has been increasingly diagnosed in patients with anterior shoulder pain and tenderness. However, studies have suggested that subcoracoid impingement may not be as rare as once thought. In fact, one study reported that 19% of patients with combined subscapularis, supraspinatus, and infraspinatus tears had subcoracoid impingement, and another reported subcoracoid impingement as a postoperative complication in 5.1% of patients following rotator cuff repair and anterior acromioplasty.
Subcoracoid impingement has been defined as the encroachment of the posterolateral coracoid process upon the lesser tuberosity of the humerus. This mechanism is common in patients who repetitively engage in activities involving forward flexion, adduction, and internal rotation because this position reduces coracohumeral distance and potentially impinges the intervening soft tissue structures. This compression of the soft tissues between the lesser tuberosity and coracoid tip has been termed the roller-wringer effect and reportedly can lead to progressive degeneration and injury to the rotator cuff, specifically subscapularis tendon tears, long head biceps tendon injuries, and anterior shoulder pain.
Anatomic variations of the humerus and scapula, specifically lesser tuberosity prominences and coracoid length/ orientation, respectively, can decrease coracohumeral distance. Modern imaging techniques have a role in the evaluation of coracohumeral distance, lending to the diagnosis and treatment of patients with subcoracoid impingement. The coracoid index, or lateral extension of the coracoid process, is subject to individual variation, and the coracohumeral interval is affected by dynamic arm positions. No specific imaging positions have been described to help interpret coracohumeral distance. Therefore, the purpose of this study was to determine the variability in coracohumeral distance and coracoid index as a function of arm rotation in healthy male subjects. Our null hypothesis was that there would be no differences in coracohumeral distance with respect to shoulder rotation.
Full Article: Coracohumeral Distances and Correlation to Arm Rotation