Workshop Summary - The Cranio-Spinal Meningeal Functional Unit (CSMFU)

Summary

Nick Hodgson conducted a workshop on the Cranio-Spinal Meningeal Functional Unit (CSMFU), focusing on the anatomy of the spinal dura mater and its role in the biomechanics of subluxations and their effects on the central nervous system, referencing DD Palmer's concept of "tone." The session highlighted the evolution of the understanding of dural attachments, moving from older textbook descriptions of a "free" spinal dura to modern recognition of a "spiderweb of ligaments" and myodural bridges – such as the connection between the rectus capitis posterior minor muscle and the dorsal spinal dura – which are considered critical normal anatomy, especially in the upper cervical spine. The discussion emphasized the clinical significance of these meningeal-vertebral ligaments and their varied orientation across the spine, which stabilize the spinal cord and prevent adverse mechanical cord tension.

Nick discussed the dilemma of whether to intervene first on the physical components of subluxation to normalize neurological tone or on the neurological tone to release adverse mechanical cord tension. He also differentiated between local subluxations without dural attachments and global subluxations with dural attachments, noting that practitioners observe differing impacts of adjustments.

Details

Workshop Introduction and Concept of Tone: Nick Hodgson began the workshop on the Cranio-Spinal Meningeal Functional Unit (CSMFU), part of continuing education on the tonal and neurological model, percussion therapy benefits, and proficiency with the 3dEnergy Gun. The session focuses on anatomy not typically covered at an undergraduate level, which is vital for understanding the nervous system's relation to the spinal system, and introduced DD Palmer's concept of "tone" as a standard from which to note variations in structure, temperature, tonicity, elasticity, renitency and tension.

Spinal Dura Mater and Subluxations: Nick reviewed the basic anatomy of the spinal dura mater, the continuation of the inner layer of the cranial dura mater, surrounding the spinal cord. The discussion centered on the potential role of the dura mater in the biomechanics of subluxations and their physiological and pathophysiological effects on the central nervous system, showing visual representations of the spinal cord wrapped in its meningeal layers. It was noted that literature has varied, controversial, and changing views on attachments between the vertebral canal and the dura mater, which are increasingly seen as normal and important anatomy rather than pathology.

Early Chiropractic and Dural Attachments: The early chiropractors, such as RW Stephenson in 1927, recognized dural attachments to bone beyond the foramen magnum and coccyx, specifically to the posterior body of C2. Nick suggested this understanding might explain the focus of pioneers like BJ Palmer on adjusting the upper cervical spine, as well as the importance given to the coccyx, the final attachment of the spinal cord. Early diagrams illustrated these fibrous attachments from the vertebrae to the dura mater and the impact of tension on the dentate ligaments.

Evolution of Understanding Dural Attachments: Nick pointed out the conflicting information found in older anatomy textbooks, such as a 1992 Moore’s Clinical Anatomy text, which described the spinal dura mater as "free within the vertebral canal" except at the foramen magnum. More advanced texts, like the 35th edition of Gray's Anatomy, began to acknowledge attachments to the posterior surface of C2 and C3, and fibrous slips connecting to the posterior longitudinal ligament, especially near the lower end of the vertebral canal. Recent studies utilizing dissections have consistently found continuity between the nuchal ligament and the posterior spinal dura at the atlanto-occipital and atlanto-axial intervals, indicating posterior attachments in the upper cervical region.

Detailed Dural-Vertebral and Muscular Connections: Researchers have identified detailed structures like meningeal myo-vertebral structures and connective tissue bridges, such as the one between the rectus capitis posterior minor muscle and the dorsal spinal dura, which Nick emphasized as critical normal anatomy. These myodural bridges, also demonstrated via MRI and cross-sections, are believed to transfer tensile forces and help monitor dural tension, preventing dural infolding during head movement, which has significant implications for treating chronic cervicogenic headaches. Subsequent research showed other muscles, including rectus capitis posterior major and obliquus capitis inferior are also involved in these connections.

Distribution and Role of Dorso Meningeal Vertebral Ligaments: Dorsal meningeal vertebral ligaments, anchoring the posterior dural sac to the ligamentum flavum or lamina, were found to occur at a rate of 100% at C1-C2 and C4-C5, with the thickest ligaments observed at C1 and C2, reinforcing the critical nature of the upper cervical spine. Nick Hodgson explained that these attachments, also called Hoffman's ligaments, connect the dura to the posterior longitudinal ligament and other spinal canal elements, functioning to prevent the dura from moving away from the bony container and the potential to traction the dural sac during disc herniation. They are more prevalent and robust in the lumbar region but present throughout the thoracic vertebral column.

Clinical Significance and Ligament Orientation: Nick noted that the high incidence of attachments in the upper cervical and lumbosacral regions (such as 97% occurrence at L5-S1) correlates with clinically significant areas in practice. The orientation of these dural attachments varies along the spine – caudal-cranial in the upper thoracic, transverse at T8-T9, and cranio-caudal at lower thoracic and lumbar levels to prevent both compression/buckling and superior/inferior distraction of the spinal cord. The presence of single-level ligaments supports the chiropractic interest in isolating single vertebral segments for therapeutic effect on the global central nervous system.

Dural Attachments and Central Nervous System Protection: Nick explained that the earlier description of a "freely floating" spinal cord has been replaced by an accurate description of a "spiderweb of ligaments" providing fibrous attachments anteriorly, posteriorly, and laterally to suspend the spinal cord centrally and maintain stable mechanical tension. The spinal cord is also suspended by the sawtooth denticulate ligaments, which are stronger in the cervical region and attach to the dura mater to distribute stresses evenly and prevent excessive loading on the brain stem.

Spinal Cord Protection and Adverse Tension: Spinal movement, particularly flexion, significantly increases tension on the spinal cord and denticulate ligaments, with total changes in canal length of 5 to 7 cm between extremes of flexion and extension. Nick emphasized that protection of the spinal cord is provided by these dural attachments, not primarily by the cerebrospinal fluid, comparing the arrangement to a suspension bridge. Finally, the concept of "cord tension" due to distortion of the meninges was recognized by early chiropractors like RW Stephenson, and later coined as "adverse mechanical cord tension" by neurosurgeon Alf Breig in 1978, describing how tension is transmitted from the dura mater to the cord via the dentate ligaments and its anchorage at the brain stem and cauda equina.

Subluxation Intervention and Mechanisms: Nick discussed the relationship between the physical components of subluxation and altered neurological tone, posing the dilemma of which should be addressed first: intervening on the physical components to normalize neurological tone or intervening on neurological tone to release adverse mechanical cord tension. Nick also differentiated between subluxations without dural attachments, which are local lesions with minimal neurological impact, and those with dural attachments, which instantly become global lesions and whose therapy will have global effects on the central nervous system. He noted that practitioners observe some adjustments having a bigger impact than others.