Bi-directional Mechanical Properties of the Axillary Pouch of the Glenohumeral Capsule: Implications for Modeling and Surgical Repair

The objective of this study was to determine the mechanical properties of the axillary pouch of the inferior glenohumeral ligament in the directions perpendicular (transverse) and parallel (longitudinal) to the longitudinal axis of the anterior band of the inferior glenohumeral ligament. A punch was used to excise one transverse and one longitudinal tissue sample from the axillary pouch of each cadaveric shoulder (n=10). Each tissue sample was preconditioned and then a load-to-failure test was performed. All tissue samples exhibited the typical nonlinear behavior reported for ligaments and tendons. Significant differences (p<0.05) were detected between the transverse and longitudinal tissue samples for ultimate stress (0.8±0.4 MPa and 2.0±1.0 MPa, respectively) and tangent modulus (5.4±2.9 MPa and 14.8±13.1 MPa, respectively). No significant differences (p>0.05) were observed between the ultimate strain (transverse: 23.5±11.5%, longitudinal: 33.3±23.6%) and strain energy density (transverse: 10.8±8.5 MPa, longitudinal: 21.1±15.4 MPa) of the transverse and longitudinal tissue samples. The ultimate stress determined for the longitudinal axillary pouch tissue samples was comparable to a previous study that reported it to be 5.5±2.0 MPa. The ratio of the longitudinal to transverse moduli (3.3±2.8) is considerably less than that of the medial collateral ligament of the knee (30) and interosseous ligament of the forearm (385), suggesting that the axillary pouch functions to stabilize the joint in more than just one direction. Future models of the glenohumeral joint and surgical repair procedures should consider the properties of the axillary pouch in its transverse and longitudinal directions to fully describe the behavior of the inferior glenohumeral ligament.