Craniocervical Instability (CCI) is an incompetence of the ligamentous and bony elements that support and hold the weight of the skull and its movements, with respect to the cervical spine. Common symptoms are vertigo, neck pain and cognitive delay. Craniocervical instability can be found in patients with hypermobility syndromes such as EDS (Ehlers-Danlos Syndrome) but may also occur as a result of neck trauma. Over the past years, some connections between some cases of ME (Myalgic Encephalomyelitis) and CCI have been discovered.
Under normal conditions, the bony elements of the cervical spine and the craniocervical junction are supported by the integrity of the ligamentous elements and the craniocervical muscular elements.
Due to an incompetence of the ligamentous and bony elements that supports both the cervical spine and the craniocervical junction, the mobility of the craniocervical junction is increased. This causes clinical symptomatology which is referred to as Craniocervical Instability, or Atlanto-occipital instability when the juction between C1 and C2 is affected.
CCI and AAI can present in hypermobility syndromes such as Ehlers-Danlos Syndrome, where there is an increase in mobility due to the hyperlaxity of the ligamentous elements. This is a result of the abnormalities in the expression, or structure, of the fibrillar collagen. However, any condition involving an intrinsic weakness of ligaments or muscles can cause an increase in mobility of the cervical spine, specifically the craniocervical junction.
The instability may also present itself following neck trauma, such as whiplash due to a car accident.
Over the past several years a small percentage of patients diagnosed with Myalgic Encephalomyelitis (ME/CFS) have been found to also be suffering from Craniocervical Instability and/or Tethered Cord. The cause of spinal affectation in this population of patients has not been established at this time. It has been hypothesized that the instability could be a result of inflammation which in turn weakens the connective tissue. A few ME/CFS patients with TC (and occasionally later developing CCI) have as adults recognized early childhood indicators that may point to congenital TC (born with TC). There is still much to be understood and researched about the connection between ME/CFS and CCI and TC. Treating the Tethered Cord and/or Craniocervical Instability can improve some ME/CFS symptoms but should not be considered a “cure.”
Craniocervical instability diagnosis is given by performing an Upright Magnetic Resonance Imaging (uMRI), or cone-beam CT scanner (CBCT), that allows for the evaluation of the craniocervical junction in an upright position as well as the evaluation of the patient’s anatomy in flexion and extension and neck rotation. In many cases, performing a supine (standard) MRI does not allow an accurate diagnosis and may be reported as “normal” or with nonspecific signs. The surgeon should evaluate the MRI and review the existence of direct signs (angle measurements and distances between bone elements of the craniocervical junction) and also the existence of indirect signs of craniocervical mobility.
The most commonly used measures in the radiological evaluation are CXA, Grabb, BDI, BAI, ADI (see below). It is extremely important to compare the clinical-radiological correlation to determine the congruence between the clinical symptomatology and the imaging.
In this group of patients, the most frequent diagnoses consist of:
1-Craniocervical instability, levels C0-C1 (Occipital-atlas).
2-Atlantoaxial instability, levels C1-C2 (atlas-axis).
3-Cranio-atlanto-axial instability, levels C0-C1-C2.
These diagnoses have important considerations for a potential surgical treatment since the location of the instability must be determined with precision to attempt to fuse only what is necessary. It should be remembered that approximately 50% of neck’s flexion/extension takes place at C0-C1-C2 levels and that up to 50% of neck’s rotation occurs at C1-C2 level. Therefore fusion in this area may imply a marked permanent reduction of the mobility of the head and neck and should always be considered before proposing a surgical procedure.
CCI surgical treatment or AAI surgical treatment must be customized considering individual case considerations.
Abbreviations: BDI: basion dens interval, CXA: clivo axial angle, BAI: basion-axial interval, ADI: Atlantoaxial interval
Surgical treatment of Craniocervical Instability usually consists of the posterior fusion of Occipital, Atlas (C1), and Axis (C2). The pedicle screws are usually placed In the Axis, though the screws can be placed in the isthmus if the patient’s anatomy requires it. The Atlas screws are generally placed in the lateral masses. In regard to the fixation of the cranium to above mentioned cervical vertebrae, it can be done mainly in two ways:
In either method, the implanted screws are joined by lateral bars. These bars are what gives rigidity to the fusion system. In most cases, bone graft is used. The bone graft is usually allograft, originated from donor bone and artificial bone material.
Preoperative and individualized evaluation of each case is extremely important since anomalies in the anatomy and trajectory of the Vertebral Artery should be ruled out. Anatomical differences in regard to dimensions and disposition of vertebral pedicles, lateral masses and other bone elements should also be assessed.
Once in the Operating Room, surgery is performed under general anaesthesia, with onsite Neurophysiological monitoring (SSEP – somatosensory evoked potentials), neuronavigational guidance and intraoperative fluoroscopy guidance. We can therefore control the spinal cord as well as the cranial and cervical nerves in order to avoid damage to these important structures. Neuronavigational assistance guides us all through the surgery, thus it diminishes (though it does not eliminate) risks while placing the screws for the fusion. Both neurophysiological monitoring and neuronavigational guidance are performed as safety measures for the patient.
Postoperatively, the patient stays at the ICU (Intensive Care Unit) two days after which the patient is transferred to the Neurosurgical Ward. Postoperative hospital stay is approximately eight days. Sitting up begins the second day after surgery and standing and walking within several days. After hospital discharge, the well-being and progress of the patient is monitored approximately once a week after hospital discharge. This ensures that everything is as it should be before flying back home. We therefore recommend our patients to stay in Barcelona for 10-15 days after discharge.
Abbreviations: BDI: basion dens interval, CXA: clivo axial angle, BAI: basion-axial interval, ADI: Atlantoaxial interval
Sources:
-Dr. Vicenç Gilete, MD, Neurosurgeon & Spine Surgeon.
-Henderson FC, Wilson WA, Mott S, Mark A, Schmidt K, Berry KJ, et al. Deformative stress associated with an abnormal clivo-axial angle: A finite element analysis. Surg Neurol Int 2010;1:30
-Schulz R, Macchiavello N, Fernández E, Carredano X, Garrido O, Diaz J, Melcher RP. Harms C1-C2 instrumentation technique: anatomo-surgical guide. Spine (Phila Pa 1976). 2011 May 20;36(12):945-50
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