The Glenohumeral Capsule Should be Evaluated as a Sheet of Fibrous Tissue: A Validated Finite Element Model

Abstract

The function of the glenohumeral capsule has typically been evaluated by isolating several discrete, ligamentous regions during experimental and computational investigations. However, recent data suggests that the regions of the glenohumeral capsule have significant interactions and function multiaxially. Therefore, examining the function of the inferior glenohumeral ligament as a discrete structure may not be appropriate. The objective of this work was to validate the predicted strain distribution and deformed shape of the inferior glenohumeral ligament using experimental data for two subject-specific finite element models: (1) a continuous model including all capsular regions, and (2) a discrete model including only the inferior glenohumeral ligament. The distribution of maximum principal strain and deformed shape of the glenohumeral capsule was determined for a cadaveric shoulder in a joint position frequently associated with dislocation (60° of glenohumeral abduction, 52° of external rotation, and a 25 N anterior load applied to the humerus). The experimental kinematics were then applied to the two finite element models constructed from the geometry and material properties from the same cadaveric shoulder and the predicted strain distributions and deformed shapes were determined. For the continuous model, the average difference between predicted strains and experimental strains was less than 5%. The predicted deformed shape was also similar to experimental data, with the anterior band of the inferior glenohumeral ligament clearly wrapped around the humeral head. In contrast, large differences existed between the strains predicted by the discrete model when compared to the experimental strains for this joint position (average difference from experimental data was 20%). In addition, the predicted deformed shape of the inferior glenohumeral ligament did not wrap around the humeral head. These differences may be attributed to neglecting the complex interactions between the anterior band of the inferior glenohumeral ligament with the neighboring capsular regions. Thus, the glenohumeral capsule should not be evaluated as several discrete structures. Rather, it should be evaluated as a single sheet of fibrous tissue.

Capsule function following anterior dislocation: Implications for diagnosis of shoulder instability

“…The joint was moved to 608 of abduction; the path of internal-external rotation was then determined by applying a 3 N-m rotation moment and a 22 N compressive force. 16,27 The compressive force ensured that the humeral head was centered within the glenoid and simulated contributions to joint stability from the negative intra-articular pressure of the capsule and the rotator cuff muscles. The positions that most closely corresponded to 608 of abduction and 08, 308, and 608 of external rotation served as reference positions for the application of the anterior load.…”

“…Previous evaluations of the strain distributions in the anteroinferior capsule showed a wide variability among shoulders. 16,22,24,27 Therefore, strain ratios were computed by normalizing the maximum principal non-recoverable strain and strain during the simulated physical exams in each element to the peak non-recoverable strain and peak strain in the intact state, respectively, for each specimen. Any elements containing strain values less than the experimental repeatability of 3.5% 16 were set to zero, which allowed differences to be detected between the intact and injured states when elements that were initially unloaded became loaded following dislocation.…”

“…16,27 Each joint was then positioned via the testing system in a position along the reference strain path. The capsule was then inflated to 0.75 psi via the rotator interval to remove folds and wrinkles in the tissue for the purpose of establishing a reference state for strain calculations.…”

Experimental validation of finite element predicted bone strain in the human metatarsal

“…As CT attenuations only provide a scalar value at each point, many studies assume isotropic elasticity (164)(165)(166)(167)(168)(169), although anisotropic material properties have also been implemented using information within the voxel (170). The elastic moduli for early isotropic models have been homogeneous (171)(172)(173), but more recent studies have used inhomogeneous materials (8,164,165,170,174-178) as they have been found to be more accurate than the models using homogeneous material properties (9,179,180).…”

A Method for Predicting Collagen Fiber Realignment in Non-Planar Tissue Surfaces as Applied to Glenohumeral Capsule During Clinically Relevant Deformation

“…The 3D positions of the strain markers were recorded in the reference strain configuration, which was determined via inflation, using a three-camera motion tracking system (Spicatek, accuracy: 0.05 mm) [33]. Simulated clinical exams were then performed on each shoulder at 60deg abduction, and 0 deg, 30 deg, and 60 deg of external rotation by applying a 25 N anterior load to the humérus while maintaining a 22 N compressive load to center the humeral head on the gienoid [13,[33][34][35]. The 3D positions of the strain markers were recorded at these three joint positions with the loading conditions applied.…”