[Roentgenological study of the lumbar spinal canal shape (author's transl)]

It is very important to understand the accurate spinal canal shape and size to solve the neurological lumbar problems. Using plain X-ray films superior notch distance (SND) on lateral film and interfacetal ratio (IFR), the ratio of the interfacetal distance and the interpedicular distance on A-P view, were measured to determine the criteria for classification of the spinal canal shapes into 4 groups as follows; 1) Trefoil canal: SND up to 4.5 mm, IFR up to 67% 2) Triangular canal: SND up to 4 mm, IFR above 80% 3) Round canal: SND above 6.5 mm 4) Intermediate canal: others. These canal shapes, according to our criteria, were shown to be in good accord with CT-images. The clinical characteristics of these typical spinal canals were also studied. 1) Trefoil canal, which had the narrow spinal canal, shallow lateral recess and long nerve root tunnel, caused the radicular disturbance in 60% and cauda equina disturbance in 68%. 2) Triangular canal, with the wide spinal canal, small lateral recess and long nerve root tunnels, caused the radicular disturbance in 28% and the intermittent claudication in 50%. 3) Round canal, with the wide spinal canal, wide lateral recess and short nerve root tunnel, caused no neurological deficits, namely "safe form". 4) Intermediate canal showed the so-called intermediate form and clinical characteristics between the 3 groups. The flattened triangular canal was one of the most important form, hardly diagnosed by the measurements on plain X-ray film, which was possible only by myelogram on which the sagittal diameter of the dural tube measured less than 12 min. The lumbar spinal canals at the upper levels showed the round canals and shifted to the triangular canals at the lower levels, because of the gradual decrease of SND and increase of IFR. The trefoil canals showed the same IFR at any levels, suggesting the developmental factor and the involvement of aging.