Cranio-cervical Instability in Patients with Hypermobility Connective Disorders – J Spine 2016 – by Fraser C. Henderson Sr. M.D
In this PDF file, Dr. Henderson explains the technical aspects of instability between the skull and upper spine. He makes clear that diagnosis requires imaging performed in flexion-extension, not static pictures, though these are non-standard views.
Cranio-cervical instability is well documented in connective tissue disorders such as rheumatoid arthritis, systemic lupus, and genetic disorders such as Down’s syndrome and Osteogenesis Imperfecta.
However, less understood are the more than fifty genetic disorders of collagen characterized by joint laxity, and of course, laxity of the ligaments of the spine.
Given the propensity in these patients for spinal instability, it is not surprising that the most severe symptoms arise in the most mobile part of the spine, the cranio-cervical junction.
The increased recognition of hypermobility syndromic disorders, of which Ehlers Danlos Syndome (EDS) is emblematic, has prompted questions and concern as to what constitutes pathological instability in this category of patients, and how to best diagnose this instability.
These questions assume significant importance, given recent epidemiological evidence that the hypermobility syndromes, exemplified by EDS, are far more prevalent than previously thought.
Whilst the clinical presentation of CCI is accepted in the population with conditions such as rheumatoid arthritis and osteogenesis imperfecta, the same clinical recognition has not been afforded to the hereditary hypermobility connective tissue disorders (HHCTD).
Radiological measurements for degenerative connective tissue disorders are standard in the neuro-radiological lexicon. However, the diagnosis of cranio-cervical instability, such that occurs in EDS, more often requires images performed in flexion-extension, and careful measurement .
While advocates for HHCTD recommend the use of dynamic imaging, arguing that ligamentous instability is usually not apparent on routine imaging performed in the supine position, opponents argue that dynamic imaging is often not available, is not standard neurosurgical practice, and that the radiological diagnosis of pathological instability at the cranio-cervical junction has not been clearly established in the literature for the hypermobility population.
The diagnosis of instability should be predicated upon the presence of a supportive history and concordant, demonstrable neurological findings.
Punjabi and White defined instability as the loss of the ability of the spine under physiological loads to maintain relationships between vertebrae in such a way that there is no damage or subsequent irritation of the spinal cord, brainstem or nerve roots.
Additionally, that instability can be considered to exist where there is development of deformity or incapacitating pain due to structural change.
The importance of dynamic imaging is that ventral brainstem compression may exist in flexion of the cervical spine, but appear normal on routine imaging.
For instance, in a survey of Chiari malformation treatment via foramen magnum decompression, surgical failures were thought to range from 20-50% .
Klekamp looked at forty-five revision decompressions for Chiari I malformation, of which ten underwent cranio-spinal fusion. He stated that deterioration after decompression, for Chiari I malformation was related to untreated basilar invagination cranio-cervical instability or recurrent CSF flow obstruction.
He emphasized the importance of signs of instability and stressed the importance of “functional studies in flexion and extension to demonstrate hypermobility at the cranio-cervical junction.
The presence of cranio-cervical instability is thought to cause pain and neurological findings through three mechanisms:
- stretch of the lower cranial nerves;
- stretch of the vertebral arteries and
- deformative stretching or deformation of the brainstem and upper spinal cord.
Neurobiological evidence of deformative stress is manifested in
- clumping of the neuro-filaments and microtubules and loss of axonal transport ,
- the formation of axon retraction balls similar to those seen in diffuse axonal injury ,
- pathological calcium influx , and
- altered gene expression .
Ligamentous laxity, inherent in HHCTD, may result in cranio-cervical instability, kyphosis of the clivo-axial angle and ventral brainstem compression.
In some patients, this causes disabling pain and neurological deficits.
Dynamic imaging appears to be helpful in the diagnosis of these challenging conditions.
The growing body of knowledge regarding the prevalence of hypermobility connective tissue disorders should lead to more widespread recognition of the lax ligament syndromes arising in the context of HHCTD at the cranio-cervical junction.