Finite element modelling of the glenohumeral capsule can help assess the tested region during a clinical exam

Abstract

The objective of this research was to examine the efficacy of evaluating the region of the glenohumeral capsule being tested by clinical exams for shoulder instability using finite element (FE) models of the glenohumeral joint. Specifically, the regions of high capsule strain produced by glenohumeral joint positions commonly used during a clinical exam were identified. Kinematics that simulated a simple translation test with an anterior load at three external rotation angles were applied to a validated, subject-specific FE model of the glenohumeral joint at 60° of abduction. Maximum principal strains on the glenoid side of the inferior glenohumeral ligament (IGHL) were significantly higher than the maximum principal strains on the humeral side, for all three regions of the IGHL at 30° and 60° of external rotation. These regions of localised strain indicate that these joint positions might be used to test the glenoid side of the IGHL during this clinical exam, but are not useful for assessing the humeral side of the IGHL. The use of FE models will facilitate the search for additional joint positions that isolate high strains to other IGHL regions, including the humeral side of the IGHL.

Figure 1

Inferior view (left shoulder) of fringe plots of IGHL 1st Principal strains at 60° degrees abduction and full anterior translation at 0°, 30°, and 60° of external rotation. (A) Humerus. (B) Glenoid. (C) IGHL Mid-line. (D) AB-IGHL. (E) Axillary Pouch. (F) PB-IGHL. The glenoid side of the IGHL is consistently loaded more than the humerus side at 30° and 60° of external rotation.

Figure 2

Maximum principal strains at 0°, 30°, and 60° of external rotation on the glenoid and humeral sides of each IGHL region. Maximum principal strains were significantly higher on the glenoid side for each IGHL region at 30° and 60° of external rotation, but not at 0°. (* p<0.05) (mean±SD).