The Inferior Glenohumeral Ligament Strains by 20% After Shoulder Dislocation.

Background: The inferior glenohumeral ligament (IGHL) contributes to anterior stability of the shoulder and elongates during anterior dislocation. However, the relationship between shoulder position and IGHL strain has not been fully elucidated. While previous studies have investigated ligament strain in abducted and externally rotated positions, no studies have examined ligament strain during internal and external rotation in a horizontally extended arm position. Furthermore, no studies have quantitatively evaluated IGHL elongation by replicating actual anterior dislocation. Purpose: To (1) measure strain in the IGHL in various shoulder positions and determine which positions contribute to anterior stability and to (2) assess strain in the IGHL and quantify ligament elongation after dislocation simulating anterior shoulder dislocation. Study Design: Descriptive laboratory study. Methods: Eight fresh-frozen cadaveric shoulders were used. The specimens were fixed in a custom-designed testing apparatus, and transducers were attached to the IGHL and axillary pouch to measure strain. The glenohumeral joint was fixed at 60° of abduction relative to the scapula. The angle of horizontal flexion-extension was varied from 30° of horizontal flexion to 30° of horizontal extension in 10° increments. Additionally, internal and external rotation angles were varied from maximal internal rotation to maximal external rotation. Strain in the IGHL was recorded for each position. Next, the arm was held at 60° of abduction and maximal external rotation and was manually extended horizontally until an anterior dislocation occurred. Strains and humeral head displacement during dislocation were measured. After dislocation, histopathological examination of specimens was performed. Results: The IGHL strain increased with the increase of horizontal extension and external rotation angles. In contrast, the strain in the axillary pouch did not change significantly with the increase of horizontal extension or external rotation angles. Anterior dislocation occurred in all shoulders. Two shoulders had Bankart lesions, 4 had bony Bankart lesions, and 2 had capsular tears. The mean maximal strain of the IGHL during dislocation was 19.9% ± 5.5%, while the maximal strain of the axillary pouch was 18.7% ± 7.5%. Histological analysis showed fiber discontinuity and disruption near both bony attachment sites, compared with the central portion of the IGHL. Conclusion: IGHL strain increased as horizontal extension and external rotation angles increased. The IGHL experienced a maximal strain of approximately 20% during an anterior dislocation. Clinical Relevance: The results of this study demonstrated that the IGHL undergoes a maximal strain of approximately 20% during an anterior dislocation. This finding may serve as a reference for determining the appropriate amount of ligamentous plication during Bankart repair. It might be appropriate to shorten the IGHL by 20% during Bankart repair.