The current anatomical description of the inferior glenohumeral ligament does not correlate with its functional role in positions of external rotation

The objective of this study was to determine the strain distribution in the inferior glenohumeral ligament at 0°, 30°, and 60° of external rotation with an anterior load applied to the joint. Five cadaver shoulders were dissected free of all soft tissue except the glenohumeral capsule and a 7 × 11 grid of strain markers were affixed to the inferior glenohumeral ligament. The location of these strain markers was then determined for a reference strain configuration and while a 25 N anterior load was applied to simulate a clinical exam for instability. The magnitude and direction of the maximum principal strains were then determined at each joint position. For all specimens, the magnitude of the maximum principal strains were significantly greater for 30° and 60° of external rotation when compared to 0° of external rotation. Furthermore, when comparing 30° to 60° of external rotation, three of the five specimens were significantly different. Additionally, the previously described regions of the inferior glenohumeral ligament could not be identified with a qualitative evaluation of the strain distribution pattern for each specimen at all external rotation angles. This indicates that our current description of the three regions of the inferior glenohumeral ligament does not correspond to its functional role. Additionally, the directions of the maximum principal strains across the inferior glenohumeral ligament became more aligned with one another as external rotation was increased. The complex strain distributions observed indicates that future studies should treat the inferior glenohumeral capsule as a continuous sheet of fibrous tissue. © 2008 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res