The effect of compressive axial preload on the flexibility of the thoracolumbar spine.
Academic Article
Overview
abstract
STUDY DESIGN: An in vitro flexibility study of the human thoracolumbar spine under compressive preload. OBJECTIVE: To attain kinematics descriptive of the thoracolumbar spine in vitro by applying a pure bending moment under a range of physiologic compressive preloads. SUMMARY OF BACKGROUND DATA: Many studies on the mechanical behavior of the spine under pure moment have been conducted; however, little is known regarding variations in the range of motion of the thoracolumbar spine attributable to simulated body weight and other physiologic load conditions. METHODS: Five fresh human cadaveric thoracolumbar spine specimens (T9-L3) were used. Five compressive axial preloads ranging from 75 to 975 N were applied to each specimen along the spinal curvature through four adjustable brackets attached to each vertebral body. Flexibility measurements were taken by applying a maximum of 5 Nm pure bending moment to the specimen in flexion and extension. The flexibilities in flexion and extension for each loading case were compared. RESULTS: The thoracolumbar spine supported compressive preloads as much as 975 N without damage or instability in the sagittal plane when the preload was applied along the natural curvature of the spine through estimated centers of rotation. The flexibility in bending (flexion/extension) of the ligamentous thoracolumbar spine decreased with increasing compressive preload. CONCLUSION: A higher bending stiffness was reached after the compressive load exceeded 500 N. Such knowledge could be used to establish better testing guidelines for implant evaluation and more realistic loading conditions.
