The second terminations of the suboccipital muscles: An assistant pivot for the To Be Named Ligament.

Xiao-Ying Yuan,Seung-Ho Han,Hong-Jin Sui,Qi-Qi Zhao,Jia-Ying Sui,Chan Li,Nan Zheng,Zhao Huang-Fu,Okoye Chukwuemeka Samuel,Sheng-Bo Yu,Xiao Zhang,Na-Na Mou,Hsin-Chih Lai

doi:10.1371/journal.pone.0177120

Abstract

In the last two decades, many studies have focused on the muscles and dense connective tissues located in the suboccipital region. Our study investigated the existence of the second terminations originating from the suboccipital muscles, and the relationship between the variable types of the To Be Named Ligament (TBNL). Anatomical dissection was performed on 35 head-neck specimens. The existence of the second terminations of the suboccipital muscles was confirmed and various types of the TBNL were observed in this study. The second terminations originated from multiple suboccipital muscles including the rectus capitis posterior minor (RCPmi), rectus capitis posterior major (RCPma) and obliquus capitis inferior (OCI) muscles, merged and terminated at the TBNL. The overall incidence of the second terminations of the suboccipital muscles was 34.29% and it varied among the various suboccipital muscle origins. 28.57% of the second terminations originated from the RCPma; 11.43% was from the RCPmi and 8.57% was from the OCI. Furthermore, there was a significant relationship between the existence of second terminations and the particular type of the TBNL. 95% of the arcuate type of the TBNL was accompanied with the second terminations which attached to their turning part, whereas only 10% of all the radiate type of the TBNL was accompanied with the second terminations. This study for the first time described the second terminations originating from multiple suboccipital muscles and demonstrated the relationship with the various types of the TBNL. We speculated that the second terminations maintain the arcuate TBNL and transfer tensile forces to the Myodural Bridge (MDB), thereby modulating the physiological functions of the MDB.

Highlights

The suboccipital region is one of the most complicated anatomical areas of the human body [1]
We termed these novel terminations as the “second terminations” and we investigated the morphological relationship between these second terminations and the variable types of the To Be Named Ligament (TBNL) in the deep suboccipital region of humans
The rectus capitis posterior major (RCPma) originated from the pcciput and the rectus capitis posterior minor (RCPmi) originated from the position between the inferior nuchal line of the occiput and the foramen magnum, descended to attach at the posterior tubercle of the atlas and the spinous process of axis respectively

Summary

Introduction

The suboccipital region is one of the most complicated anatomical areas of the human body [1]. In 1995, Hack et al first described the relationship between the deep suboccipital muscles and the cervical spinal dura mater. They found a connective tissue bridge named the Myodural Bridge (MDB), between the rectus capitis posterior minor (RCPmi) and the dorsal cervical spinal dura mater at the atlanto-occipital interspace. The RCPmi gave off dense connective tissue that connects with the posterior atlanto-occipital membrane, and merged with the dorsal cervical spinal dura mater [2]. Many studies in the last decade have shown that the MDB originate from multiple suboccipital muscles including the rectus capitis posterior major (RCPma) and the obliquus capitis inferior (OCI) [4,5,6,7,8,9,10,11,12,13]

Methods

Results

Conclusion