In extension of the cervical spine, the ligamentum flavum (LF) may bulge and intrude into the vertebral canal and cause symptoms of myelopathy and/or radiculopathy in patients with canal stenosis. Knowledge of the relationship between the extension angle
and the physiologic changes of the LF is important for a better understanding of the clinical symptoms. The current study was designed to demonstrate the dynamic correlativity of canal intrusion of the LF bulge with the extension angle
of the cervical spine.
With a novel method, the probe of the electrical resistance strain gauge was put into the cervical canals of 14 cadaveric specimens. The LF bulge distance of six segments (C2–C3 to C7–T1) and corresponding extension angles of every 5° from 0° to 45° were collected. Angle–bulge curves were drawn.
In overextension (45°), C5–C6 had the biggest canal intrusion depth (3.478±0.527 mm), whereas the upper and lower segments declined gradually (C5–C6>C4–C5>C6–C7>C3–C4>C7–T1>C2–C3). The curves in all segments were sigmoidal, which demonstrated the dynamic change of LF, that is, during the process of extension, LF shortened and contracted first, after the original length was reached, it began to bulge and burst into the canal.
The current study has provided a method to measure inner canal kinematic changes in intact spinal specimens.