Calculation of Intervertebral Disc Pressure in the Thoracic and Lumbar Spine in Elderly Women with Kyphosis Using a Novel Musculoskeletal Model with Isolated Thoracic Vertebrae and Rib Cage

摘要

Background: Degeneration of the intervertebral disc is one of the causes of kyphosis. Several biomechanical studies have investigated the mechanisms of development of spinal deformity using simulation models. Realistic musculoskeletal models are helpful for investigating the pathophysiology and changes in internal forces in patients with kyphosis. However, the association between intervertebral disc pressure and kyphosis has not been fully elucidated to date. Purpose: To calculate intervertebral disc pressure in elderly women with kyphosis using a novel and precise thoracolumbar three-dimensional musculoskeletal model. Materials and Method: Ten female patients with a mean age of 80.0 ± 6.5 years who visited our hospital for medical examination of osteoporosis were included. The subjects were divided into the normal and kyphosis groups depending on their sagittal vertical axis. Intervertebral disc pressures in the thoracic and lumbar spines of subjects were analyzed by inverse dynamics analysis using a novel three-dimensional musculoskeletal model, and were compared between the groups. Result: Significant differences in lumbar lordosis (LL) were observed between the two groups. Furthermore, the kyphosis group was older and shorter. In the kyphosis group, the upper thoracic vertebrae (T1 - T6) showed significantly higher intervertebral pressure than the normal group. Conclusion: Intervertebral disc pressure in the thoracic and lumbar spines of patients with spinal deformities was evaluated using a novel thoracolumbar three-dimensional musculoskeletal model. Using this novel model with separated thoracic spine and modified muscle path reflecting actual physiological curvature, disc pressure closer to the realistic condition was obtained. Intervertebral disc pressure in the upper thoracic spine in the kyphosis group was significantly increased compared with that in the normal group. Moreover, intervertebral disc pressures in the upper thoracic spine correlated negatively with LL.