Stratificational relationship among the main nerves from the dorsal division of the sacral plexus and the innervation of the piriformis

Abstract

In order to comprehend more completely the morphology of the nerves to the piriformis, it is necessary to obtain a detailed understanding of the relationship of the origin and the course of these nerves from the dorsal division of the sacral plexus, with reference to the superior and inferior gluteal nerves. Twelve of seven human pelvic halves were carefully dissected in order to examine the origins of the nerves from the dorsal division of the sacral plexus. Six of these pelvic halves were further dissected under a stereomicroscope to examine the nerves to the piriformis.1. The origin of the superior gluteal nerve was more proximal and dorsal in the sacral plexus than that of the inferior gluteal nerve.2. The superior gluteal nerve consisted of a thick cranial part and a thin caudal part; the former continued as the inferior branch of the nerve, and the latter, the superior branch. The cranial and caudal parts crossed before reaching the glutei medius and minimus.3. The nerves to the piriformis arose from three main nerves from the dorsal division of the sacral plexus: 1) the caudalmost root of the superior gluteal nerve, 2) the caudal roots of the inferior gluteal nerve and 3) the common peroneal nerve. Considering the stratificational relationship among the main nerves from the dorsal division of the sacral plexus, the piriformis appears to be composed of parts from different muscle layers. o

An appraisal of the short lateral rotators of the hip joint

“…Table shows the variations in the patterns of innervation of short lateral hip rotators as identified in anatomical textbooks, accompanied by analysis from cadaveric primary studies (Akita et al, ; Aung et al, ; Yadav et al, ) and review articles (Petchprapa et al, ; Petrie et al, ). In a detailed morphological investigation of the innervation of piriformis, Akita et al () observed multiple branches of the “nerves to the piriformis” in 12 Japanese cadavers, all arising from the nerves of posterior rami of the sacral plexus. From first six cadavers, Akita et al () noted branches arising from the caudal part of the superior gluteal nerve (6 of 6), the inferior gluteal nerve (3 of 6) and the common fibular nerve (1 of 6).…”

“…Akita et al (1994) used the former description in the 49 specimens they investigated, whereas in later studies, Nork et al (2005) (n 5 14) and Solomon et al (2010) (n 5 20) identified the piriformis origin using the latter terminology. In an earlier study, Akita et al (1992) described a variation in origin from "first to third pelvic sacral foramina" on one of the six specimens studied. Other textbooks McKinley and O'Loughlin, 2006) and an additional cadaveric study of four specimens (Snijders et al, 2006) describe the origin of piriformis from the anterolateral surface of the sacrum.…”

Lower Limb Nerve Supply

“…The origin of the superior gluteal nerve was found to be dorsal and more proximal to the origin of the inferior gluteal nerve (Akita et al, 1992). The origin of the superior gluteal nerve was found to be dorsal and more proximal to the origin of the inferior gluteal nerve (Akita et al, 1992).…”

Piriformis Syndrome

“…Akita et al have studied the innervation of piriformis and glutei medius and minimus. [23][24][25] Based on the detailed findings of the innervation of the three muscles, they concluded that the muscle fibres of piriformis are chiefly composed of the caudal element of the gluteus medius muscle (89.8%) and in some cases the caudal element of the gluteus minimus muscle as well (10.2%). 24 The peroneal part of the sciatic nerve lies in the tissue plain superficial to gluteus minimus, and the tibial part of the sciatic nerve lies deep to this tissue plain, so when a portion of piriformis is formed by the gluteus minimus muscle layer, it divides the sciatic nerve.…”