Static and Dynamic Torque in the Modulation of the Caudal Vertebral Growth

Background/Objective: Major research demonstrates that longitudinal loading affects the vertebral growth and disc wedging in the scoliotic animal models; however, there is a scarcity of research on the effect of torque on the vertebral growth. Comparison of the effect of static and dynamic torque on growth is also lacking. The aims of this study were to assess the morphological, histological, and immunohistochemical changes in caudal vertebrae of rats under controlled, static, and dynamic torque. Methods: Adjacent vertebral bodies of female Sprague-Dawley rats were loaded with a torque for 4 weeks. Six rats received a static torque of 1.25 Nm while 6 additional rats received a dynamic torque (2.4 Nm, 1.0 Hz for 15 min/time, 3 times/week). An additional 6 rats formed the control group and received no torque at all. All the rats were later sacrificed, and the tails for histological analysis, immunocytochemistry, and X-rays were obtained. Results: Among the three groups, there were significant differences in right side disc height and average disc height on the proximal vertebrae space in the coronal plane of the X-ray. There were significant differences in the physeal height between static torque and control, or between dynamic torque and control (p < 0.05). The proliferating cell nuclear antigens were detected with variable percentages in samples among the three physeal zones for all groups. Conclusions: Both static and dynamic torque induced asymmetric reduction in the physis and intervertebral disc, which may help to explain the development and vertebral tethering of scoliosis.