Measurements of the lumbar spinal canal in 2 racial groups.

Direct measurements of 1,340 lumbar vertebrae in 275 skeletons in two racial groups are reported. The average figure, and the upper and lower limits of normal are reported for the anteroposterior diameter of the canal and for Spinal Index. Radiological studies have established a technique for defining the posterior margin of the spinal canal on plain X-ray films. It is formed by a line joining the apex of the superior to the inverted apex of the inferior articular facet. The Spinal Index is not a reliable factor. The anteroposterior diameter alone is the essential parameter in assessing spinal stenosis. The negroid canal is marginally less spatial than that of the caucasoid.