A study on the relative motion trajectory of lumbar pedicles under physiological loads in vivo

Abstract

Purpose: There are limited data on the natural kinematics of the lumbar pedicle in vivo. This study investigated the range of motion of the lumbar pedicle screw insertion point when normal subjects moved under physiological loads. Methods: Ten healthy volunteers aged 25 to 39 years were recruited. A combination of a dual fluoroscopic imaging system (DFIS) and CT technology was used. With computer assistance, a three-dimensional reconstructed model of each segment of the lumbar spine was created by using the subject's lumbar spine CT and matched to dual oblique X-ray fluoroscopic images of the lumbar spine in different active positions captured by the DFIS. The combination can accurately reproduce the three-dimensional motion state of lumbar intervertebral bodies under physiological load. By measuring the changes in the three-dimensional coordinate system of the simulated pedicle screw insertion point, the in-body kinematic data of adjacent lumbar pedicles under physiological load were finally obtained. Results: During flexion and extension, the lumbar pedicle screw insertion point deviated <3 mm along the cranial axis (P<0.05) and rotated <4° around the mediolateral axis (P<0.05). During left–right bending movements, the lumbar pedicle screw insertion point deviated along the mediolateral and cranial axes (P<0.05), with the largest deviation (<2.5 mm) on the mediolateral axis at the L3–4 segment, and rotated <5° around the anterior–posterior axis (P<0.05). During left–right rotation, the lumbar pedicle screw insertion point deviated <2 mm along the cranial axis (P<0.05). Its primary rotation axis was the cranial axis, <3° around the coupling axis and the anterior-posterior axis (P<0.05). There were differences in the deviation measurement of the left and right sides during flexion-extension and bending, as well as in the true distance of the pedicle screw insertion point during bending (p<0.05). Conclusion: The movement patterns of the lumbar pedicles are inconsistent under different postures, and there is left and right asymmetric movement. Coupling will occur during complex movements.