ANATOMIC CHANGES OF THE SPINAL-CANAL AND INTERVERTEBRAL FORAMEN ASSOCIATED WITH FLEXION-EXTENSION MOVEMENT

Study Design. A cadaveric study was done to analyze the dimensional ch anges in the spinal canal and intervertebral foramen of the lumbar spi ne with flexion and extension movements. Objectives. To investigate th e relationship between flexion and extension movements and morphologic changes in the spinal canal and the intervertebral foramen. Summary o f Background Data. Previous studies have reported that the dimensions of the spinal canal and the intervertebral foramen may change signific antly with motion. The purpose of this study was to assess the quantit ative changes in the spinal canal and the intervertebral foramen with segmental flexion-extension movements. Methods. Nineteen fresh cadaver ic spines yielding 25 motion segments were used. The lumbar segments w ere frozen and then imaged in axial and sagittal projections by a comp uted tomography scanner. They were thawed then, and the motion segment s were loaded to 5.7 Nm in flexion (13 motion segments) and in extensi on (12 motion segments) specimens. While in flexion or extension, the specimens again were frozen and imaged by computed tomography scan. Th e frozen specimens then were sliced using a cryomicrotome in the sagit tal plane to study the dimensions of the intervertebral foramen. Eight een other fresh cadaveric spines were sliced sagittally for study in t he neutral position. Results. The axial computed tomography scans show ed that extension significantly decreased the canal area, midsagittal diameter, and subarticular sagittal diameter, whereas flexion had the opposite effects. The sagittal computed tomography scans showed that e xtension decreased all the foraminal dimensions significantly, whereas flexion increased all the foraminal dimensions significantly. The tra nslational changes were associated with the bulging of the disc and th e presence of traction spurs. The cryomicrotome sections showed the cr oss-sectional area of the foramen to be 12% greater for the flexion gr oup and 15% smaller for the extension group than the cross-sectional a rea of the neutral group. Nerve root compression in the foramen was fo und to be 21.0% in neutral, 15.4% in flexion, and 33.3% in extension g roups. Conclusions. This study supports the concept of dynamic spinal stenosis. In addition to static anatomic changes, careful dynamic stud ies may be required to evaluate better the central canal and the foram en.