Dynamic changes of the cervical ligamental flavum in hyperextension---hyperflexion movement and their measurements.

Ten fresh cadaver cervical spine specimens were frozen and bisected through the median sagittal plane. The length, thickness of the ligamental flavum (LF) and its protruding depth into the cervical canal were measured in hyperextension, hyperflexion and mid-position. The results showed that LF was elongated and became thinner in hyperflexion and shortened, thickened, and protruded into the cervical canal in hyperextension. The protruding depth into the canal was 3.5 +/- 0.35 mm at C 5-6, 3.25 +/- 0.50 mm at C 4-5 and 2.96 +/- 0.35 mm at C 6-7 respectively. Segmental stenosis was observed at the level of intervertebral space in hyperextension.