[BIOMECHANICAL STUDY ON UPPER THORACIC SPINE BASED ON PRESSURE SENSITIVE FILM MATERIALS IN CHINESE MINI PIGS]

To analyze the pressure change and distribution of the intervertebral disc of upper thoracic spine in vertical pressure and 5° flexion, extension, or lateral bending.

Twelve thoracolumbar spinal specimens were harvested from mini pigs and were divided into 2 groups (n=6). T_{1, 2}, T_{3, 4}, T_{5, 6}, and T_{7, 8} segments were included in one group, and T_{2, 3}, T_{4, 5}, T_{6, 7}, and T_{8, 9} segments were included in the other group. The data from both groups represented the complete upper thoracic vertebra data. Biomechanical machine and pressure sensitive film were used to measure the pressure on the vertebral columns under loadings of 100, 150, and 200 N in vertical pressures and 5° flexion, extension, or lateral bending. The pressure change of each intervertebral disc under different loads and in different movement conditions was analyzed.

In flexion, the anterior annulus pressure of the upper thoracic vertebra increased (P<0.05), whereas the posterior annulus pressure showed no significant change (P>0.05) or an increasing trend (P<0.05). In extension, the anterior annulus pressure of the upper thoracic vertebra decreased (P<0.05), whereas the posterior annulus pressure decreased (P<0.05) or had no obvious change (P>0.05). In lateral bending, the pressure on the concave side of the annulus increased significantly (P<0.05).

The upper thoracic vertebra has unique biomechanical characteristics under different loadings; moreover, the posterior vertebral structure plays an important role in the movement of the upper thoracic vertebral segment and pressure distribution. In lateral bending of the upper thoracic vertebra, the concave side pressure will increase significantly, which suggests that asymmetrical force is an important cause of scoliosis progression. Gravity plays an important role in the progression of scoliosis.