Anatomic changes of the spinal canal and intervertebral foramen associated with flexion-extension movement (Spine 1996;21:2412-2420)

1. Study design: Cadaveric Study (Lumbar spine)

2. General information about stenosis
 1)Central canal stenosis (not too much reliable)
    >>Less than 10mm midsagittal canal diameters: Absolute Stenosis
    >>Less than 13mm: Relative Stenosis
 2) Lateral canal stenosis (formainal stenosis)
    >> Enterance Zone/Mid-Zone/Exit Zone
    >> 5mm lateral recess height: Normal
    >> 2mm or less: Absolutely pathologic
    >> 3-4mm: suggestive of lateral recess stenosis
    >> caused by subluxation of superior facet/ disc herniation/ protruding anulus/osteophyte
    >> Foraminal height: 11~19mm/  Foraminal area: 40~160㎟
    >> 4mm posterior disc height or less: critical
    >> 15mm or less foraminal height: critical

3. Objectives
  1) investigate the changes in dimensions of spinal canal and foramen
  2) investigate the changes in nerve root compression during flexion and extension

4. Number of subjects: 37 cadavers (15 men/ 22 women), 35-87 y (mean 68.6y)

5. Grouping
  1) group 1: neutral (18 cadavers)
  2) group 2: flexion (9 cadavers)
  3) group 3: extension (10 cadavers)

6. Levels
  1) Group 1 >>19: L1/2, L2/3, L3/4, 22: L4/5, 12: L5/S1
  2) Group 2 and 3 >> 19: L2/3, L4/5 or L1/2, L3/4, L5/S1

7. Measurments

  Axical parameter measurements
   1. Mid-sagittal diameter of canal
   2. Subarticular sagittal diameter of canal
   3. Thickness of the ligamentum flavum

  Sagittal parameter measurements
   1. Anterior Disc Height
   2. Midpoint Disc Height
   3. Posterior Disc Height
   4. Foraminal Height
   5. Upper foraminal width
   6. Middle foraminal width
   7. Lower foraminal width
   8. Posterior bulging of the disc
   9. Distance of osteophyte from endplate of superior vertebral body
   10. distance of osteophyte from endplate of inferior vertebral body
   11. Vertebral body angulation
   12. Vertebral body translation

8. Results

Spinal Canal

In flexion (CT)
 1. Cross-sectional area, midsagittal diameter, subarticular sagittal diameter of the canal >> increased significantly
 2. Cross-sectional area of ligamentum flavum >> decreased

In extension (CT)
 1. Cross-sectional area, midsagittal diameter, subarticular sagittal diameter of the canal >> decreased significantly
 2. No significant changes in thickness or in cross-sectional area of ligamentum flavum

In Specimens
 1. Flexion-extension affected the absolute stenosis group the most
 2. statistically significant correlation between midsagittal diameter of canal and cross sectional area of canal
 3. No statistically significant correlations between any parameter and the changes in translation and angulation

Foramen

In flexion (CT)
 1. Increased all foraminal dimensions
 2. Most significant changes for foraminal cross-sectional area

In extension (CT)
 1. Decreased all foraminal dimensions
 2. Decreased middle foraminal width and foraminal cross-sectional area
 3. Significant posterior translation of vertebral body and increased posterior bulging of disc

In Compressed nerve root group
 1. significantly smaller posterior disc height, middle foraminal width, foraminal cross-sectional area than normal
 2. Significantly large posterior bulging of disc (p<0.05)


Translation changes >> associated significantly with posterior bulging of disc (P<0.005)

9. Discussion

CT data
 1. Increased the size of central canal (11%) in flexion
 2. Decreased the size of canal (11%) in extension
 3. Increased foraminal area (12%) in flexion
 4. Decreased foraminal area (15%) in extension

Cryomicrotome data
 1. Cross-sectional areas of foramina >> 15 ㎟ (12%) in flexion group/ 19㎟ (15%) smaller in extension group than normal
 2. Incidence of nerve root compression >> 21% in neutral group/ 15.4% in flexion group/ 33.3% in extension group

Morphology of nerve root and surrounding structures in foramen
 1. Usually compressed by facet subluxation
 2. associated with bulging of the posteriornferior portion of ligamentum flavum
 3. smaller disc heights, foraminal dimensions, cross-sectional foraminal areas

10. Conclusion
The study supports the concept of dynamic spinal stenosis. In addition to static anatomic changes, careful dynamic studies may be required to evaluate better the central canal and the foramen