Fetal development of deep back muscles in the human thoracic region with a focus on transversospinalis muscles and the medial branch of the spinal nerve posterior ramus

Abstract

Fetal development of human deep back muscles has not yet been fully described, possibly because of the difficulty in identifying muscle bundle directions in horizontal sections. Here, we prepared near-frontal sections along the thoracic back skin (eight fetuses) as well as horizontal sections (six fetuses) from 14 mid-term fetuses at 9-15 weeks of gestation. In the deep side of the trapezius and rhomboideus muscles, the CD34-positive thoracolumbar fascia was evident even at 9 weeks. Desmin-reactivity was strong and homogeneous in the superficial muscle fibers in contrast to the spotty expression in the deep fibers. Thus, in back muscles, formation of the myotendinous junction may start from the superficial muscles and advance to the deep muscles. The fact that developing intramuscular tendons were desmin-negative suggested little possibility of a secondary change from the muscle fibers to tendons. We found no prospective spinalis muscle or its tendinous connections with other muscles. Instead, abundant CD68-positive macrophages along the spinous process at 15 weeks suggested a change in muscle attachment, an event that may result in a later formation of the spinalis muscle. S100-positive intramuscular nerves exhibited downward courses from the multifidus longus muscle in the original segment to the rotatores brevis muscles in the inferiorly adjacent level. The medial cutaneous nerve had already reached the thoracolumbar fascia at 9 weeks, but by 15 weeks the nerve could not penetrate the trapezius muscle. Finally, we propose a folded myotomal model of the primitive transversospinalis muscle that seems to explain a fact that the roofing tile-like configuration of nerve twigs in the semispinalis muscle is reversed in the multifidus and rotatores muscles.

Hitherto unknown detailed muscle anatomy in an 8‐week‐old embryo

“…*Facial nerve muscles: the muscles innervated by the facial nerve were not present in our specimen except for the stylohyoid and posterior belly of digastric muscle. ** Sato et al (2011) did not identify this muscle, but Mekonen et al (2016) did.…”

“…The existence of the spinalis muscle at CS23 is controversial. Based on the observed location, the muscle could not be found in a study assessing 7-to 13-week-old fetuses (Sato et al 2011) but was present at a stage 23 human embryo according to Mekonen et al (2016). In concordance with Mekonen et al (2016), the spinalis muscle was also identified (Fig.…”

A Best-Evidence Systematic Appraisal of the Diagnostic Accuracy and Utility of Facet (Zygapophysial) Joint Injections in Chronic Spinal Pain

“…The following have been put forth to be the basis for pain: an osteophyte impinging on a nerve, a capsule being stretched, synovial villi being trapped within articular surfaces, and chemicals that cause an inflammatory reaction (64,66,(68)(69)(70)(71)(72)(73)(74)(75)(76)(77). Facet joints also have been shown to be richly innervated by the medial branches of the dorsal rami (35,70,(78)(79)(80)(81)(82)(83)(84)(85)(86)(87)(88)(89)(90)(91). In addition to this innervation, neuroanatomic, neurophysiologic, and biomechanical studies have shown that facet joints have both free and encapsulated nerve endings and that they also have nerves that contain substance P as well as calcitonin gene-related peptide (CGRP) (62,64,74,75,80,81,.…”

Relationship Between the Ischiotibial and Paravertebral Muscles and Low Back Pain

“…They are located in the posterior vertebral spine and their function is the keep the torso upright while we are standing or sitting. [17][18][19][20][21][22] There is a close relationship between the paravertebral muscles and low back pain. Studies to evaluate the muscle strength of patients with mechanical low back pain have found severe hypotrophy of the paravertebral musculature of these patients among their results, showing the close relationship between mechanical low back pain and weakness of the paravertebrals.…”