Effect of low back posture on the morphology of the spinal canal.
OBJECTIVE
To define the possible mechanism of posture-dependent symptoms of spinal stenosis by measuring the effect of low back posture on morphologic changes of the intervertebral discs and spinal canal in healthy young people.


METHODS
Twenty healthy young volunteers underwent magnetic resonance imaging while supine with their spine in neutral, flexed, extended, and right and left rotational positions. The axial MR images at the middle of the intervertebral discs of L3-4 and L4-5 were analyzed to measure the difference in the size and shape of the intervertebral discs and spinal canal in each posture.


RESULTS
Extension or rotation decreased the sagittal diameters and cross-sectional areas of the dural sac and spinal canal and increased the thickness of the ligamentum flavum, whereas flexion had the opposite effects. The gap between the convex posterior disc margin and the anterior margin of the facet joint on each side, represented as the subarticular sagittal diameter, increased with flexion and decreased with extension or rotation. The direction of rotation did not result in asymmetry of the subarticular sagittal diameter, but right rotation caused thickening of the right ligamentum flavum, and vice versa. The shape and dimensions of the disc did not change significantly according to the positions of the low back.


CONCLUSIONS
With extension or rotation, the thickness of the ligamentum flavum increased and the posterior margin of the intervertebral disc was approximated to the facet joint without any change in shape and size of the disc. These phenomena result in a decrease in the size of the spinal canal and dural sac in extension or rotation postures in young healthy people without disc degeneration, and may explain the posture-dependent symptom of spinal stenosis.
Chung
S S
SS
Department of Orthopaedic Surgery, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea.
Lee
C S
CS
Kim
S H
SH
Chung
M W
MW
Ahn
J M
JM
D000328:Adult; D000704:Analysis of Variance; D005260:Female; D006801:Humans; D007403:Intervertebral Disc / Q000033:anatomy & histology / Q000502:physiology; D017843:Ligamentum Flavum / Q000033:anatomy & histology / Q000502:physiology; D008159:Lumbar Vertebrae / Q000033:anatomy & histology* / Q000502:physiology*; D008279:Magnetic Resonance Imaging; D008297:Male; D012399:Rotation; D013115:Spinal Canal / Q000033:anatomy & histology / Q000502:physiology; D013130:Spinal Stenosis / Q000175:diagnosis; D016683:Supine Position / Q000502:physiology