Dynamic changes in the dimensions of the lumbar spinal canal: An experimental study in vitro

The variation in the dimensions of the lumbar spinal canal under both flexion‐extension and axial compression‐distraction was studied using computerized tomography (CT) scans in human cadaver lumbar spine specimens. In 3‐mm‐thick CT slices through the disk at L3‐L4, the cross‐sectional area of the spinal canal was reduced by around 40 mm2, corresponding to a 16% reduction of the initial area when the lumbar spines were moved both from flexion to extension and from distraction to compression. A corresponding reduction in the midsagittal diameter of the canal of 2 mm was found. During these motions, the ligamentum flavum did not appear to be a significant factor for the dynamic changes affecting the dimensions of the canal. This held true even after the disk had been excised in order to produce a total collapse of the disk space.