Purpose: This study was conducted to define what portion of the subscapularis tendon is visualized during standard diagnostic glenohumeral arthroscopy and to determine the distance between the inferior aspect of the visible portion of the subscapularis tendon and the axillary nerve.
Type of study: Anatomic (cadaveric) analysis.
Methods: Six fresh-frozen human cadaveric shoulders were placed in a simulated lateral decubitus position with longitudinal traction and 45 degrees of shoulder abduction. Glenohumeral arthroscopy was performed on each specimen using a standard posterior portal for visualization. The 4 corners of the visible portion of the subscapularis were tagged with arthroscopic sutures. The shoulders were subsequently dissected. The surface area defined by the 4 suture tags and the surface area of the entire subscapularis tendon were calculated for each specimen. The dimensions of these areas and the distance between the inferior aspect of the visible portion of the subscapularis tendon and the axillary nerve were measured with calipers.
Results: The arthroscopically tagged portion of the subscapularis tendon represented only a small percentage (26% +/- 11%) of the entire tendon. The majority of the subscapularis tendon is veiled by the middle and inferior glenohumeral ligaments. There was a significant distance between the inferior aspect of the visible portion of the subscapularis tendon and the axillary nerve (32.8 +/- 6.0 mm). The mean height of the visible portion of the tendon represented 44% of the mean overall height of the subscapularis.
Conclusions: These data suggest that arthroscopic visualization of the subscapularis is incomplete. Lesions involving the concealed portion of the subscapularis tendon may not be detected arthroscopically. The wide margin of safety between the inferior aspect of the visible portion of the subscapularis tendon and the axillary nerve is relevant to the placement of anteroinferior (trans-subscapularis) arthroscopy portals as well as to performing arthroscopic anterior capsular releases.