To investigate the biomechanical effects of different flexion angles of the annular ligament on elbow joint stability. Methods
Left elbow CT and MRI scans were chosen from a healthy volunteer, according to a previous research model. A cartilage and ligament model was constructed with SolidWorks software according to the MRI results to simulate the annular ligament during normal, loosen, and rupture conditions at different buckling angles (0, 30, 60, 90, 120). In 15 elbow models, boundary conditions were set according to the literature. The different elbow 3D finite element models were imported into ABAQUS software to calculate and analyze the load, contact area, contact stress and stress of the medial collateral ligament of the olecranon cartilage.
1. According to the analysis results, olecranon cartilage stress values when the annular ligament under different conditions（normal、loosened、ruptured）with elbow extension, were 2.1 ± 0.18, 2.4 ± 0.75, and 2.9 ± 0.94 MPa. As the buckling angle increased, the stress value decreased; with 120 degrees of elbow flexion, the minimum stress values were 0.9 ± 0.12, 1.1 ± 0.38, and 1.2 ± 0.29 MPa. 2. When the contact surface of the olecranon cartilage was flexed from 0 to 30 degrees, the olecranon cartilage contact area significantly increased, reaching a maximum value of 254±5.35 mm, and then the contact area gradually decreased, reaching a minimum value of 176±2.62 mm when the elbow joint was flexed to 120 degrees. The results when the annular ligament was loosened and ruptured were different from those of the normal annular ligament. The maximum values were 283±4.74and 312±5.49mm at 60 degrees of elbow flexion. The contact area gradually decreased with an increase in the angle, and the minimum values were 210±3.82 and 236±6.59 mm at 120 degrees of elbow flexion. 3. When the elbow joint was extended, the maximum stress of the medial collateral ligament was 6.5±0.23, 11.5±0.78 and 18.7±0.94 MPa under different states; as the stress decreased with an increase in the angle, the corresponding values were 2.8±0.18, 4.8±0.56 and 6.2±0.72 MPa at 120 degrees of elbow flexion.
The annular ligament plays an important role in maintaining elbow joint stability. When the annular ligament ruptures, it should be reconstructed as much as possible to avoid the elevation of stress on the surface of the medial collateral ligament of the elbow and on the annular cartilage, which may cause clinical symptoms.