[Finite element analysis of the influence of anchorage number and location on Bankart repair strength of shoulder joint].

Objective: To study the influence of the number and position of anchor nails on the Bankart repair by the finite element analysis.

Methods: The 3D CT data of shoulder joints including normal adult volunteers were imported into Mimics 10.0 and Geomagic 2012 software to reconstruct the related tissues, and then meshed in Hypermesh 13.0 software to give material attributes. The position and number of MPC constraints were adjusted in Abaqus 6.14 to establish finite element model of shoulder joint under 6 working conditions including A model(normal control model), B model (Bankart damage control model), C model (1 anchor), D model (2 anchors), E model (3 anchors), F model (4 anchors). The humerus external rotation and forward load were added to simulate the fear test of the shoulder joint forward instability.

Results: (1)Normally, the inferior glenohumeral ligament complex accompanied by the external rotation of the humerus head has a wrinkle and a significant stress concentration around its anterior and posterior bundle terminations.(2)The stress of the anterior bundle and posterior bundle of the inferior glenohumeral ligament were increased by 52.33% and 45.67% respectively after Bankart's injury.(3)In each model of anchor repair, the stress concentration was obvious at the anchor site, and the stress of anterior and posterior bundle ligaments could be reduced; there were no obvious differences between C, D models and B model(>0.05), and there were significant differences between E, F models and B model(<0.05).

Conclusions: One or two anchors can reduce the stress of the anterior and posterior bundles of the inferior glenohumeral ligament in the repair of Bankart's injury, but when the angle of rotation is large, the stress concentration in the anchor position increases significantly, leading to the increases of the risk of failure. The application of three or four anchors can enhance the constraints on the inferior glenohumeral ligament and reduce the stress of the anchor itself through the "load sharing" effect between anchors, so as to ensure the stability of the shoulder joint and provide a mechanical environment for the early rehabilitation of patients.