Effect of glenohumeral ligaments on posterior shoulder stabilization: a biomechanical study.

OBJECTIVES

To theoretically confirm that the glenohumeral ligament (GHL), specifically the inferior glenohumeral ligament (IGHL), plays an important role in posterior shoulder stability in different postures, and to provide reference for clinical diagnosis and treatment of posterior shoulder instability (PSI).

MATERIALS AND METHODS

In this retrospective study, bone-ligament-bone models were established in 15 fresh adult shoulder joint specimens and selective cutting was performed for analysis. The humeral head was loaded posteriorly at a central pressure of 22N using the INSTRON8874 biomechanical testing system and the load-displacement curve was plotted. The posterior displacement of the humeral head was measured after continuous cutting of the following structures: (1) complete; (2) superior glenohumeral ligament (SGHL); (3) SGHL + middle glenohumeral ligament (MGHL); (4) SGHL + MGHL + IGHL; (5) MGHL; (6) MGHL + IGHL; (7) anterior-bundle IGHL (IGHL-AB); (8) posterior-bundle IGHL (IGHL-PB); (9) IGHL. The results obtained were analyzed using the SPSS10.0 statistical software.

RESULTS

Favorable posterior stability of the complete bone-ligament-bone model was observed, with an average displacement of 11.32±3.89 mm. The displacement of SGHL and SGHL + MGHL groups was not significantly increased compared with that in the complete group (P>0.05). After cutting of SGHL + MGHL + IGHL, the posterior displacement of all angles increased (P<0.05), resulting in PSI that was manifested in dislocation or subluxation. There was no obvious increase in posterior displacement after cutting the IGHL-AB (P>0.05). Significantly increased posterior displacement was observed at 45° abduction after cutting the IGHL-PB compared with the complete group, but not at the 90° abduction. The posterior displacement increased obviously at both 45° and 90° abduction when the IGHL was completely cut off (P<0.05).

CONCLUSIONS

Repairing the IGHL plays a certain role in rebuilding the posterior stability of the shoulder joint. Detecting the function of the IGHL in the abduction and external rotation positions of the shoulder joint has certain significance for diagnosing PSI.