Triangle Tilt Surgery: Effect on Coracohumeral Distance and External Rotation of the Glenohumeral Joint

Objective: Shoulder muscle imbalances and bone deformities that develop secondary to obstetric brachial plexus injury have been extensively studied. Less emphasis has focused on coracohumeral distance, a small value potentially being linked to impaired shoulder external rotation. The purpose of this study is to analyze coracohumeral distances and shoulder external rotation in obstetric brachial plexus injury patients before and after triangle tilt surgery. Methods: Twenty patients with deformities secondary to obstetric brachial plexus injury were included. Coracohumeral distances were measured on computed tomographic images. Clinical functioning was evaluated through video recordings by using a modified Mallet scale. Paired Student t tests were used to determine statistical significance of anatomic and functional parameters, pre- and postoperatively. Results: Coracohumeral distance (P < .0006), total Mallet score (P < .0001), supination angle (P < .0001), and individual Mallet scores for all external rotation parameters including hand-to-mouth (P < .0001), supination (P = .0010), external rotation (P < .0001), hand-to-neck (P < .0001), and hand-to-spine (P = .0064) were significantly higher postoperatively than preoperatively for affected shoulders. Hand-to-mouth angles were significantly lower postoperatively than preoperatively (P < .0001). Coracohumeral distance in unaffected shoulders remained unchanged. Conclusions: Triangle tilt surgery significantly improves coracohumeral distance and clinical functioning in obstetric brachial plexus injury patients. Coracohumeral distance plays a key role in shoulder external rotation. Increasing coracohumeral distance significantly improves all external rotation parameters and total Mallet scores. The triangle tilt surgery relieves excessive tightness of the anterior stabilizing complex, widens coracohumeral distance, and improves external rotation of shoulder.