Abstract: BACKGROUND: Most of the biomechanical studies on kyphosis have focused on trunk muscle strength and sagittal plane balance, and little has been reported on the biomechanical response within the spine during kyphosis.
OBJECTIVE: To investigate the biomechanical response of the spine during postural kyphosis by simulating the process of postural kyphosis.
METHODS: A three-dimensional finite element model of the normal thoracolumbar segment (T1-S1 segment) was established by using the finite element method. 10 groups of pure bending loads from 1.15-11.52 N·m were applied using a three-point force system on T1, T6, and T12 vertebrae to simulate the process of postural kyphosis in normal humans. The relationship between the loads and Cobb angle and the biomechanical responses of vertebrae, ribs, and intervertebral discs were analyzed. 
RESULTS AND CONCLUSION: (1) During postural kyphosis, the Cobb angle size of T1-T12 segments was linearly related to the load size. (2) The maximum stresses on the vertebrae, ribs, and intervertebral discs increased with increasing load. (3) Under the action of 11.52 N·m moment, the maximum stresses on the vertebral body, ribs, and intervertebral disc were found in the front of the T6 vertebral body, the rib head of the 10th pair of ribs, and the right posterior side of the intervertebral disc of the T5-T6 segments. (4) The results of this study suggest that postural kyphosis leads to increased stress on the vertebrae, ribs, and discs, with the most significant increase in stress on the anterior side of the T6 vertebrae, at the rib head of the 10th pair of ribs, and on the anterior side of the disc at the T5-T6 segment, as well as on the posterior side, which may increase the risk of injury to the vertebrae, ribs, and discs, which provides a biomechanical basis for the design of kyphosis orthoses.

Key words: postural kyphosis, finite element analysis, biomechanics, spine, Cobb angle