Anterior shoulder anatomy and subcoracoid impingement: An anatomical study

The aim of our study was to describe the anatomy of the anterior shoulder, specifically structures potentially involved in subscapularis tears pathophysiology and also to identify structures at risk during surgical approaches of this area.

We designed an observational, experimental study based on cadaveric models. Dissection was performed and several structures of the anterior shoulder were characterized including the subscapularis, coracoid morphology, the coracoacromial ligament, coraco-humeral distance, and the axillary and musculocutaneous nerves.

Our sample included 16 shoulders. The coracoacromial ligament presented two bands in 37.5%, and these variants were significantly wider and thinner, and were associated with inferior coraco-humeral distance in internal rotation. The subscapularis footprint was longer and the coracoid process was bigger in male specimens, and the median coracoid angle was 122°, corresponding to a Leite-Torres type I. The Subscapularis showed a median thickness of 0.7cm, while the coraco-humeral distance in our sample ranged from 0.30cm in internal rotation to 0.85cm in external rotation. Neurologic relevant structures were at least more than 2.55cm from the coracoid tip.

This is the first paper to explore the eventual relationship between the presence of a double band coracoacromial ligament variant and subcoracoid impingement. Also, to our knowledge, this is the first cadaveric model study to postulate a possible anatomic base for subcoracoid impingement, as the SS myotendinous junction thickness was found to be greater than the coraco-humeral distance in neutral position and in IR.