The Central Neural System in Hypermobility

This article is primarily a summary of information I presented during a lecture entitled "Cervical Spine and pathoneuromechanics" for the EDS ECHO program in May 2022.

Clinicians working with patients with Hypermobility Spectrum Disorders (HSD) often note a broad range of symptoms of apparently disordered central neurological function in these clients. There are a range of diagnostic labels that may be applied to explain the presence of these symptoms, indicating comorbid conditions that appear to occur more commonly in those with HSD such as Chiari malformations, Intracranial Hypertension, Intracranial Hypotension or spontaneous spinal CSF leaks, Occult Tethered Cord Syndrome or Craniocervical Instability. A huge challenge for patients and clinicians alike, is that differentiating between these different “conditions” can be very challenging with significant overlap of symptoms, lack of precise clinical tests and diagnostic criteria, and potentially a high rate of co-occurrence.

Until such time as we have a substantial body of research to explain the pathology and management options for patients with these symptoms, it can be helpful to explore the basic sciences and models from other conditions in an attempt to understand mechanisms that may underlie the symptoms and therefore guide potentially valuable interventions. Many manual therapists are already aware that adverse mechanical loading of nerve structures can impact their neurological function. Aberrant tension and compression can impact nerve tissue in many ways, including by disruption of the vascular supply to the nerve, the flow of axoplasm within the nerve or physical damage to the fibres themselves. Thanks to the work of individuals like Robert Elvey, Michael Shacklock and David Butler some of these concepts have been part of the undergraduate education of Australian physios for many years. Before them, Alf Breig’s work (1, 2) provided an invaluable description of “normal” and pathological mechanics of the central nervous system (CNS). Breig outlines a range of clinical cases where pathology such as space occupying lesions or adhesion of the cord and meninges to adjacent structures contributed to altered mechanics of the CNS which in turn generated symptoms of dysfunction in areas throughout the CNS, often quite remote from the causative lesion, such as a lesion at the top of the spinal cord causing “sciatic pain” and bowel and bladder dysfunction ((2) pp159-160)

Recent research is beginning to shed light on some of the mechanisms potentially underlying symptoms that are witnessed all too often in individuals with HSD. In the past two years, researchers have developed new techniques to visualise the movement of the CNS caused by pulsation of the cerebrospinal fluid (CSF) that bathes it (a pulsation often considered merely a nuisance and impediment to obtaining clear images of the structures in the past) (

Myodural Bridge
The Myodural Bridge (MDB): Rectus Capitis Posterior Major and Minor & Obliquus Capitis Inferior connect to the cervical dura through the OC1 and C12 interspaces

A study published the same year by Klinge and colleagues demonstrated an increase in this pulsatile motion of the upper cord in a group of patients with Ehlers-Danlos Syndrome (EDS) as well as altered movement of the cord within the central canal of the spine during neck flexion and extension movements(3). They also identified a range of structural changes in the myodural bridge, a fairly recently identified connection between the dura that surrounds the spinal cord and a number of the muscles connecting the skull and upper cervical vertebrae (rectus capitis posterior major, rectus capitis posterior minor and obliquus capitis inferior). In an article published this year, Klinge and colleagues identified further structural changes potentially impacting the spinal cord mechanics of EDS patients, this time in the filum terminale which connects the lower end of the cord to the coccyx(4). They found the filum of the hypermobile EDS patients to have impaired elasticity and suggested this may leave it less able to dampen forces transmitted to the cord.

When all of the interacting factors that influence how the central nervous system adapts to bodily movement are considered, including the structure of the tissues within the neural system and those connecting it to other body structures, and the influence of CSF on both supporting the CNS and the meningeal coverings around it as well as inducing movement through the pulsation of the fluid that occurs with the cardiac and respiratory cycle, many hypotheses may arise as to factors that could contribute to neurological dysfunction in individuals with HSD. Labuda and colleagues have published a paper this year attempting to connect all these aspects together in generating a hypothesis to explain why some patients with Chiari malformation visible on imaging develop symptoms while many do not (5). They propose an interaction between overload of the myodural bridge due to chronic instability of the upper cervical spine, potentially changing the compliance of the dura to which it attaches and therefore reducing the ability of that dura to attenuate the peak pressures of the CSF pulsation. They go on to suggest that these increased peak pressures could over time cause mechanical damage to neurological structures in the area. It seems possible that even without the cerebellar herniation characteristic of Chiari, many of these factors could be interacting in some HSD sufferers. Further, with alterations in the composition of two structures anchoring the spinal cord at opposing ends (the myodural bridge and the filum terminale) the spinal cord of EDS sufferers could be subjected to abnormal mechanical loading during normal bodily movements.

Much further research is clearly needed to fully understand the mechanisms that may be at play in generating neurological symptoms in patients with HSD and optimal treatment interventions to address these issues. In the meantime, however, the knowledge, clinical reasoning and assessment skills of manual therapists who understand the normal anatomy and mechanics of the neural system and the potential vulnerabilities in patients with HSD should enable them to clinically assess for modifiable factors potentially contributing to aberrant mechanical loading of the CNS and to address these factors in ways that may alleviate symptoms and halt or slow further deterioration of neurological function. Improving functional control of the spine and reducing sources of nerve entrapment or adverse mechanical loading throughout the neural system may be able to improve the function of the CNS in a meaningful way for these patients.

It is encouraging that much is happening in this space and I’m excited to be working with an international group exploring some of these issues and attempting to generate a clinical consensus on management of craniocervical instability. Ideally this will be a springboard to significant further exploration and research in this area which can only help in improving the management options available to patients with these conditions.

1. Breig A. Adverse mechanical tension in the central nervous system: An analysis of cause and effect: Relief by functional neurosurgery: J. Wiley; 1978.

2. Shacklock M. Biomechanics of the Nervous System: Breig Revisited2007.

3. Klinge PM, McElroy A, Donahue JE, Brinker T, Gokaslan ZL, Beland MD. Abnormal spinal cord motion at the craniocervical junction in hypermobile Ehlers-Danlos patients. Journal of Neurosurgery: Spine. 2021;35(1):18-24.

4. Klinge PM, Srivastava V, McElroy A, Leary OP, Ahmed Z, Donahue JE, et al. Diseased Filum Terminale as a Cause of Tethered Cord Syndrome in Ehlers-Danlos Syndrome: Histopathology, Biomechanics, Clinical Presentation, and Outcome of Filum Excision. World Neurosurgery. 2022.

5. Labuda R, Nwotchouang BST, Ibrahimy A, Allen PA, Oshinski JN, Klinge P, et al. A new hypothesis for the pathophysiology of symptomatic adult Chiari malformation Type I. Medical hypotheses. 2022;158:110740.

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