[Perforation of dorsal branches of the sacral nerve plexus through the piriformis muscle and its relation to changes of segmental arrangements of the vertebral column and others].

To determine whether perforation of the dorsal branches arising from the sacral nerve plexus through the piriformis muscle is dependent on segmental migration of the vertebral column and others, the relationships between the perforating nerves (Fig. 1) and changes in the segmental composition of the following items were studied morphologically and statistically in 224 Japanese adults. Each of items 1) to 8) was classified in some mode or type depending on its composition and appearance. 1) Based on the length of the 8th rib and costal cartilage and whether or not the 8th to 10th ribs attached to the costal arch, the forms of the arch were classified into 6 types (Fig. 2-1). Type E, quoted commonly in many textbooks, in which the 8th to 10th ribs are all joined to the arch, was found in only 8 (6%) of 126 sides. A true 8th rib was found in 2 (3%), and a floating 10th rib was found in 59 (95%) of 62 sides. 2) The length of the 12th rib and costal cartilage, measured by a wet thread put on its inner surface, was classified into 4 types (Fig. 3-1): lacking (in this condition, the lumbar costal process appeared in 9 (2%) of 380 sides), short, normal (the length ranged from 5.1 cm to 13.4 cm) and long. Length varied from about 3 cm to 18.2 cm, with most cases concentrated in a range of 8 cm-14 cm. 3) Based on the number of presacral vertebrae, the vertebral column was classified as short (prefixed), normal, normal in number but abnormal in composition, and long (postfixed) (Table 4-1). The true "normal" type of 12 thoracic and 5 lumbar vertebrae was found in 196 (88%) of 224 bodies. Eleven thoracic and 5 lumbar, 13 thoracic and 4 lumbar, and 13 thoracic and 5 lumbar vertebrae were found in one body each, and thoracolumbar and lumbosacral vertebrae in 2 and 5 bodies, respectively. The long type of vertebral column appeared about twice as often as the short type. 4) Based on the height and appearance of the sacral promontory in the median plane, it was divided into 7 types (Fig. 5-1). The normal type, in which the promontory lay on the tip of the first sacral (25th) vertebra and projected sharply into the pelvic cavity, was found in 158 (71%) of 224 bodies.(ABSTRACT TRUNCATED AT 400 WORDS)