2022, Vol. 26 ›› Issue (18): 2812-2816

Orthopedic force applied to the rib influences the displacement and rotation angle of thoracic vertebrae: a finite element analysis

Ren Dong1, Zhu Ye1, Lei Lei1, Wang Yuren2   

Abstract: BACKGROUND: Scoliosis not only causes a shift of the vertebral body in the coronal plane, but also causes vertebral rotation. Vertebral rotation is rarely considered in the correction of scoliosis, which weakens the correction effect.   
OBJECTIVE: To analyze the loading condition of the orthopedic force, and standardize the force application zone, release zone, orthopedic force magnitude and force area at the three-dimensional level through a finite element model.
METHODS: Based on the CT data of a 14-year-old adolescent with idiopathic scoliosis, a finite element model of the upper and lower ribs of the thoracic vertebra and the convex side of the parietal vertebra was established, and uniform orthopedic forces of 20, 40, 60, and 100 N were applied to the dorsal region, lateral region and anterior region of the ribs, respectively. Reference points were selected on the vertebral body to record displacement and rotation angle under different working conditions.   
RESULTS AND CONCLUSION: Applying orthopedic force to the lateral area had the most obvious effect on scoliosis correction. The Cobb angle was corrected from 29° to 19° under 60 N to a small area, and the coronal plane was corrected by 4.5 mm. Applying force to the dorsal area had the most obvious effect on the rotation and correction of the vertebral body. Applying force to a large area could relatively gently rotate the adjacent vertebral body. When applying 100 N force to a large dorsal area, the rotation of the apex vertebral body was corrected by 76.9%, while applying force to the anterior area aggravated the rotational distortion of the vertebral body. All these findings indicate that applying force to a small area should be selected for coronal plane correction and applying a force to a large area should be selected for vertebral rotation correction. The lateral area should be selected for coronal orthopedic force. The force applied to the convex dorsal region is beneficial to the correction of vertebral rotation, while the force applied to the anterior region is unfavorable to the correction of vertebral rotation and had little effect on vertebral rotation. Therefore, in the three-dimensional thoracic orthopedic surgery, the lateral side of the convex, the dorsal area, and the anterior area of the concave should be set as the area that the force is applied, and the other areas should be set as the release area.
Key words: CT images, vertebral rotation, reverse engineering, biomechanics, orthopedic force, idiopathic scoliosis, three-dimensional orthosis, finite element