Study design: In vivo, quasi-static distortion of the human cervical spinal cord was measured in five volunteers during flexion of the neck using a motion-tracking magnetic resonance imaging technique.
Objectives: To measure cord distortion and movement in living subjects.
Summary of background data: In situ spinal cord measurements in human and rhesus monkey cadavers taken at full flexion demonstrate that the entire cervical cord elongates approximately 10% of its length at a neutral position, but no data are available at other angles of flexion, or in living subjects.
Methods: The spatial modulation of magnetization pulse sequence created a series of parallel lines in the image that deform with the tissue. A custom-designed device was built to guide the flexion of the neck and enhance motion reproducibility. Midsagittal plane images were acquired before and after flexion. The tagged line pattern in each pair of magnetic resonance images was compared to compute distortion and movement of the cervical spinal cord at varying degrees of flexion.
Results: Between a neutral posture and full flexion, the entire cord (C2-C7) elongated linearly with head flexion, increasing 10% and 6% of its initial length along the posterior and anterior surfaces, respectively. Average displacement was on the order of 1-3 mm, and varied with region. Specifically, the upper cord showed caudad movement in the spinal canal, and the lower cord moved cephalad, again with larger movements on the posterior surface.
Conclusions: The cervical cord elongates and displaces significantly during head flexion in human volunteers, offering valuable information regarding the normal milieu of the cord.