Dynamic analysis of cervical spinal canal morphological changes and intervertebral disc strain during cervical flexion using three-dimensional non-contact optical strain detection technique

English Keywords:Cervical spinal stenosis  Digital image correlation(DIC) technique  Spinal canal morphology  Intervertebral disc strain  Ligamentum flavum stretching

English Abstract:

  【Abstract】 Objectives: To quantitatively evaluate the patterns of changes in spinal canal sagittal diameter, intervertebral disc(IVD) strain and ligamentum flavum stretching during cervical flexion motion, and to provide a reference for the non-surgical treatment strategies for cervical spinal stenosis(CSS). Methods: Six fresh-frozen adult cervical spine specimens(C0-T1, mean age 45.7±10.3 years) were sectioned along the mid-sagittal plane to expose the spinal canal structures. Specimens were loaded with dynamic buckling motion(from 15° extension to 45° flexion, with 5° intervals) using a custom-designed arc-shaped fixture. The digital image correlation(DIC) system was adopted to capture in a non-contact way the IVD strain(E)(with anterior, middle, and posterior regions denoted as E1, E2, and E3, respectively), spinal canal sagittal diameter change(D), and ligamentum flavum stretching degree(L). Linear regression analysis was performed to examine relationships between these parameters and flexion angles as well as cervical segments. Results: (1)With increasing flexion angle, progressive increases in E, D, and L were observed across all cervical segments. (2) At C2/3, C3/4, C4/5, C5/6, and C6/7 segments, E1, E2 and E3 showed significant linear positive correlations with flexion angle(P<0.05); At C2/3, C3/4, C4/5, and C5/6 segments, D demonstrated linear positive correlation with flexion angle(P<0.05); At C3/4, C4/5, C5/6, and C6/7 segments, L showed linear positive correlation with flexion angle. (3) At 10° extension, E2, E3, and L progressively increased with descending cervical segments(P<0.05); At extension 5°, E2, E3, D, and L progressively increased with descending cervical segments(P<0.05); In neutral position, E1, E2, E3, D, and L progressively increased with descending cervical segments(P<0.05); At 5° and 10° flexion, E3, D, and L progressively increased with descending cervical levels(P<0.05); At 15° flexion, D and L progressively increased with descending cervical segments(P<0.05); At 20°, 25°, 30°, 35°, 40°, and 45° flexion, L progressively increased with descending cervical segments(P<0.05). (4) With increasing flexion angle, significant positive correlations between D and L were observed at C2/3, C3/4, C4/5, and C5/6 segments(P<0.05). Conclusions: DIC technique enables synchronous dynamic observation of cervical spinal canal morphology and related structures during continuous flexion-extension motion of the cervical spine. From extension to flexion, the sagittal diameter of the spinal canal gradually increases, accompanied by marked inereases in ligamentum flavum tension and posterior IVD strain.