[An anatomical study of the root sleeve emergence and its relation to segmental anomalies of the lumbo-sacral spine].

An anatomical study was done of 102 plexuses in 51 human white cadavers, of which 35 had normal segmental arrangement of the lumbo-sacral spine and 16 transitional vertebrae. The lumbo-sacral plexus was symmetric in 42 specimens, and asymmetrical in 9. In normal segmental arrangement of the lumbo-sacral spine, the normal type of plexus occurred in 86.7% of the dissections, and prefixed type in 3.3%. In lumbarization, 8 out of 18 plexuses presented the postfixed type of plexus, and this corresponded to one half of the partial type of lumbarization. In sacralization, 6 out of 14 plexuses showed the prefixed type of plexus, and this also corresponded to one half of the complete type of sacralization. In those instances in which the lumbar spine was diminished in number, as evidenced by the shortening of the 12th ribs, 23.5% of the plexuses have shifted cranially.