Stress and strain in the anterior band of the inferior glenohumeral ligament during a simulated clinical examination

Abstract

The objective of this research was to predict, with a finite-element model, the stress and strain fields in the anterior band of the inferior glenohumeral ligament (AB-IGHL) during application of an anterior load with the humerus abducted. The stress and strain in the AB-IGHL were determined during a simulated simple translation test of a single intact shoulder. A 6-degree-of-freedom magnetic tracking system was used to measure the kinematics of the humerus with respect to the scapula. A clinician applied an anterior load to the humerus until a manual maximum was achieved at 60 degrees of glenohumeral abduction and 0 degrees of flexion/extension and external rotation. For the computational analysis, the experimentally measured joint kinematics were used to prescribe the motion of the humerus with respect to the scapula, whereas the material properties of the AB-IGHL were based on published experimental data. The geometry of the AB-IGHL, humerus, and scapula was acquired by use of a volumetric computed tomography scan, which was used to define the reference configuration of the AB-IGHL. Strains reached 12% along the inferior edge and 15% near the scapular insertion site at the position of maximum anterior translation. During this motion, the AB-IGHL wrapped around the humerus and transferred load to the bone via contact. Predicted values for von Mises stress in the ligament reached 4.3 MPa at the point of contact with the humeral head and 6.4 MPa near the scapular insertion site. A comparison of these results to the literature suggests that the computational approach provided reasonable predictions of fiber strain in the AB-IGHL when specimen-specific geometry and kinematics with average material properties were used. The complex stress and strain distribution throughout the AB-IGHL suggests that the continuous nature of the glenohumeral capsule should be considered in biomechanical analyses. In the future, this combined experimental and computational approach will be used for subject-specific studies of capsular function and could provide quantitative data to help surgeons improve methods for the diagnosis and treatment of glenohumeral instability.