Elsevier

The Spine Journal

Volume 13, Issue 5, May 2013, Pages 558-563
The Spine Journal

Basic Science
Histological analysis of the rectus capitis posterior major's myodural bridge

https://doi.org/10.1016/j.spinee.2013.01.015Get rights and content

Abstract

Background context

In recent literature, a soft-tissue communication between the rectus capitis posterior major (RCPma) muscle and the cervical dura mater has been identified. To the best of our knowledge, this communication has yet to be validated from a histological perspective nor has it been examined for neural tissue.

Purpose

The purpose of this study was to examine the composition and true continuity of the communication between the RCPma and the dura mater at a microscopic level. The communication was also inspected for the presence of proprioceptive neurons.

Study design

An anatomical and histological analysis of a novel structure in the atlantoaxial interspace.

Methods

Gross dissection was performed on 11 cadavers to remove the RCPma, the soft-tissue communication, and a section of posterior cervical dura mater as one continuous unit. Paraffin embedding and sectioning followed by hematoxylin and eosin staining was conducted to validate the connection. Staining with antineurofilament protein fluorescent antibodies was performed to identify proprioceptive neural tissue on one specimen, and all findings were recorded via photographic documentation.

Results

Histological investigation revealed a tendinous matrix inserting into both the RCPma and the posterior aspect of the cervical dura mater in all 11 specimens. In the one specimen examined for neural tissue, antineurofilament protein fluorescence revealed proprioceptive neurons within the communication. Immunoperoxidase staining demonstrated the insertion of these neurons into both the dura mater and the belly of the RCPma.

Conclusions

The existence of a true connection between the RCPma and the cervical dura mater provides new insight in understanding the complex anatomy of the atlantoaxial interspace. The presence of a neural component within this connection suggests that it may serve another function aside from simply anchoring this muscle to the dura mater. Such a connection may be involved in monitoring dural tension and may also play a role in certain cervicogenic pathologies. This study also supports previous reports that no true membrane joins the posterior arch of the atlas to the laminae of the axis and contradicts the conventional belief that the ligamentum flavum joins these two structures.

Introduction

Studies dating back to the 1920s describe soft-tissue attachments between the cervical dura mater and the posterior aspects of the atlas and axis [1]. Disregarded for some time, studies of these dural attachments have resurfaced and are the subject of increasing interest in the current literature [2]. Further analysis has revealed fibrous communications linking both the rectus capitis posterior muscles and the obliquus capitis inferior (OCI) muscle to the cervical dura mater [3], [4], [5], [6], [7], [8], [9], [10] (Fig. 1).

In 1992, Kahn et al. [3] conducted an investigation focusing on the posterior intervertebral spaces of the craniovertebral joints. In this study, the atlantooccipital interspace was found to contain a tissue bridge connecting the dura mater to the rectus capitis posterior minor (RCPmi) muscle. Examination of the atlantoaxial interspace revealed similar bridges between both the rectus capitis posterior major (RCPma) muscle and the OCI.

In 1995, Hack et al. [4] published a study that further examined the soft-tissue bridge between the RCPmi and the dura mater. This study focused specifically on the myodural communication and, in doing so, brought the suboccipital region under careful examination once again. It is now widely accepted that a true anatomical connection exists between the RCPmi and the cervical dura mater in the atlantooccipital interspace [4], [11], [12]. Histological interpretation revealed that the RCPmi fascial connection fuses with the posterior atlantooccipital membrane, which ultimately coalesces with the cervical spinal dura [8], [9], [11]. It has been suggested that this myodural bridge plays a role in a variety of clinical manifestations, most notably cervicogenic headaches [4], [13]. In one case, excision of the connection led to chronic headache relief [14].

In 2011, the first anatomical study was published on the soft-tissue bridge between the RCPma and the dura mater [10]. From a gross anatomical perspective, this soft-tissue communication appeared to be similar in nature to that of the RCPmi (Fig. 2). Evidence now supports that the contents of the atlantoaxial interspace include fibrous tracts originating from both the RCPma and the OCI, which attach to the cervical dura mater [3], [10]. The atlantooccipital interspace contains similar soft-tissue components, which link the RCPmi to the dura mater [4], [8], [9], [11], [12]. It should also be noted that the ligamentum nuchae was thought to have a similar communication with the cervical dura mater through the atlantoaxial interspace [12], [15], but this hypothesis was rejected in 2005 and is still under investigation [9].

Although the anatomical existence of these communications has been previously demonstrated, their origin and functions remain a matter of debate. It has been proposed that these soft-tissue fibers serve to monitor cervical dural tension during movements of the head and neck, but there is no direct evidence to support this [4], [10], [12], [13]. The purpose of our study was to histologically evaluate the continuity of the myodural communication between the RCPma and the cervical dura mater and to examine the myodural bridge for proprioceptive neurons.

Section snippets

Methods

A total of 11 human cadavers (6 males and 5 females) were examined in this study. Four cadavers (one male and three females) were selected at random from the Department of Anatomical Sciences at St. George's University, School of Medicine. Another seven specimens (five males and two females) were selected at random from the Department of Anatomical Sciences at Logan College of Chiropractic.

The objective of these dissections was to isolate the RCPma, a small section of cervical dura mater, and

Results

Histological analysis revealed that in all 11 samples, the communication between the RCPma and the dura mater was tendinous in nature. The tissue in all samples inserted directly into the RCPma and also attached to the posterior surface of the cervical dura mater (Figs. 3 and 4). In the one specimen analyzed for neurons, binding of antineurofilament protein indicated the presence of proprioceptive neurons throughout the length of the tissue (Fig. 5). Further staining with immunoperoxidase

Discussion

The myodural communication between the RCPma and the dura mater provides new insight in understanding the complex anatomy of the atlantoaxial interspace. This study supports the suggestion by Kahn et al. [3] that no true membrane joins the posterior arch of the atlas to the laminae of the axis, which contradicts the conventional belief that the ligamentum flavum joins these two structures [11].

The contents of the atlantoaxial interspace were previously described as dense conjunctive tracts

Acknowledgments

The authors would like to thank the Department of Anatomical Sciences at both St. George’s University School of Medicine and Logan College of Chiropractic for provision of cadaveric specimens and Jan Ryerse, PhD, at the Research Microscopy Core in the Department of Pathology at St. Louis University for the preparation and interpretation of histological data. The authors would also like to thank graduate students Patrick Battaglia and Sharonrose Samelak for assisting with dissections, Steven

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FDA device/drug status: Not applicable.

Author disclosures: FS: Nothing to disclose. MEP: Nothing to disclose. DEE: Research Support (Investigator Salary): Logan College (D, Paid directly to institution/employer); Grant: HRSA (D, Paid directly to institution/employer). EM: Nothing to disclose.

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