Arthroscopic anatomy medial to the coracoid: an anatomic study of the axillary and musculocutaneous nerves

Purpose The purpose of this study was to provide arthroscopic measurements and orientations of the axillary and musculocutaneous nerves medial to the coracoid. Methods A retrospective chart review of 29 patients undergoing arthroscopic subscapularis repair and arthroscopic cadaveric dissection of 23 shoulders was used to analyze neuroanatomical distances to arthroscopic landmarks and to document the orientations of the axillary and musculocutaneous nerves using a clock face analogy. The clock face data was analyzed by separating the clock face into four quadrants and the frequency of any crossing nerve within each of the four quadrants was then determined. Results In vivo, the axillary nerve was found 1.5 +/- 0.5 cm medial to the coracoid tip and the musculocutaneous nerve was found 1.6 +/- 0.6 cm medial to the coracoid tip. In cadavera, the axillary nerve was found 2.0 +/- 0.6 cm medial to the coracoid tip and the musculocutaneous nerve was found 1.5 +/- 0.5 cm medial to the coracoid tip. The posterosuperior quadrant of the subcoracoid space contained a crossing nerve in 4 of 29 (13.8%) patients undergoing arthroscopic rotator cuff repair medial to the coracoid, compared to 9 of 23 (39.1%) cadavera undergoing arthroscopic dissection medial to the coracoid. The posteroinferior quadrant contained a crossing nerve in 16 of 29 (55.2%) patients compared to 17 of 23 (73.9%) cadavera. Conclusions The axillary and musculocutaneous nerves run in close proximity to the coracoid tip and coracoid arch, most consistently within 1-2 cm medial to these structures, which is closer than has been previously documented in the literature. Crossing nerves are least frequently encountered within the posterosuperior quadrant of the subcoracoid space medial to the coracoid, followed by the posteroinferior quadrant. Arthroscopic dissection of this space should begin in the posterosuperior quadrant and carefully progress to the posteroinferior quadrant to decrease the risk of intraoperative nerve injury. Given the close proximity and frequently encountered nerves in this area, extreme caution must be exercised when working arthroscopically within the subcoracoid space.