Atlantoaxial Instability (AAI): Precise Diagnosis and Specialized Management

What is Atlantoaxial Instability?

Atlantoaxial Instability (AAI), can also be referred as atlantoaxial subluxation (AA subluxation), refers to a pathological increase in the mobility between the first cervical vertebra (C1, or Atlas) and the second (C2, or Axis). This occurs primarily due to incompetence of the ligamentous elements stabilizing the atlantoaxial joint, commonly seen in patients with hypermobility syndromes such as Ehlers-Danlos Syndrome (EDS) and Marfan syndrome. In some cases, it appears alongside Craniocervical Instability (CCI), particularly in EDS patients, where instability may affect multiple segments from C0 to C2.

This abnormal mobility can be present in a neutral head position or induced during neck rotations, and it often leads to compression of neural elements, compromised venous return (such as internal jugular vein compression), and debilitating cervicomedullary symptoms.

Core Symptoms of AAI

Symptoms can be diffuse and easily misattributed to other conditions, delaying diagnosis. The hallmark signs include:

Headache and cervical pain (aggravated by neck rotation)
Occipital headaches
Brain fog and concentration difficulties
Blurred vision or visual fluctuations
Syncope or presyncope
Palpitations and dysautonomia
Weakness or tingling in arms and legs
Gait instability or coordination issues
Compression of internal jugular vein
Bow hunter syndrome

Increased joint mobility at C1-C2 leads to direct or indirect signs of cervicomedullary syndrome, affecting patients’ autonomy and quality of life. Many patients suffer for years before obtaining a correct diagnosis.

Diagnostic Imaging and Clinical Evaluation

Accurate diagnosis of AAI is complex and goes beyond a standard MRI. At Promohealth SL in Barcelona, we use advanced imaging protocols:

Upright cone-beam CT (uCBCT). Flexion-extension
3D CT rotational reconstructions
Cervical cineradiology (where needed)

We assess:

CXA: Clivo-Axial Angle
BDI/BAI: Basion-Dens and Basion-Axial Intervals
Grabb-Oakes measurement

It is critical to always perform a clinical-radiological correlation—analyzing symptoms in conjunction with radiologic evidence. AAI may appear isolated or coexistent with CCI. In patients with EDS, instability is commonly multisegmental and can extend to subaxial levels (C3-C7).

Individualized Preoperative Assessment

Every case is thoroughly evaluated to minimize surgical risk and personalize treatment. Pre-surgical planning includes:

Cervical CT scans for surgical planning
Analysis of vertebral artery anatomy and bone element layout
Evaluation of comorbidities common in EDS patients (e.g., POTS, Mast Cell Activation Syndrome, cardiac anomalies) and treatment if necessary.

After the preoperative imaging, intraoperative neuronavigation planning is finalized to define screw trajectories and anatomical relationships with precision (intraoperative CT scan and neuronavigation). This personalized analysis ensures greater safety and accuracy during surgery.

Treatment Options: Conservative and Surgical

Non-Surgical Options

When possible, non-invasive strategies are prioritized:

Cervical stabilization with custom-made orthoses
Physical therapy targeting proprioception and motor control
Autonomic and anti-inflammatory support
Neuromodulation and regenerative techniques
Immunomodulatory evaluation and treatment if needed

Surgical Intervention

The surgical treatment for Atlantoaxial instability, when it manifests alone without occipitocervical instability, mainly consists of a posterior fusion of the first cervical vertebra (C1 or Atlas) and the second cervical vertebra (C2 or Axis).

Surgical technical steps include:

In the Axis (C2), pedicle screws are usually the first choice. However, depending on the patient’s anatomy, isthmic screws or laminar screws may be considered.
In the Atlas (C1), screws are generally placed in the lateral masses.
The Atlas and Axis screws are then connected on each side by lateral bars, forming the instrumented fusion system.
In most cases, bone graft is placed, usually allografts (bone bank).

When Atlantoaxial instability occurs along with Craniocervical Instability (occipitocervical instability), posterior fusion is extended to the skull using occipital screws, resulting in a C0-C1-C2 fusion.

This procedure must always be preceded by personalized anatomical evaluations, especially to:

Rule out anomalies of the vertebral arteries
Assess the layout and dimensions of vertebral pedicles, lateral masses, and other bone elements

What Happens in the Operating Room?

Once in the operating room, surgery is performed under general anesthesia, with:

Neurophysiological monitoring (SSEP – somatosensory evoked potentials)
Neuronavigation guidance
Intraoperative CT scan

These techniques help monitor the spinal cord and cranial/cervical nerves to avoid damage to critical structures. Neuronavigation significantly reduces the risk during screw placement by ensuring precision.

Postoperative Recovery

Postoperative care includes:

1–2 days in the Intensive Care Unit (ICU)
Transfer to the Neurosurgical Ward for approximately 6–7 days
Mobilization starts on day 2-3 post-op

After discharge, weekly outpatient evaluations are conducted. Patients, especially those traveling internationally, are recommended to stay in Barcelona for 10–15 days after discharge to ensure full stabilization before returning home.

Recovery and Prognosis

With appropriate preoperative evaluation and diagnosis, many patients experience a drastic improvement in pain, neurological function, and overall quality of life. Cases involving accurate diagnosis and timely surgery, especially among EDS patients, often lead to positive long-term outcomes.

Frequently Asked Questions (FAQs)

How is AAI different from CCI?

AAI affects the C1-C2 joint(s) and vertebraes, while CCI involves the junction between the skull (C0) and cervical spine (C1). Many cases involve both CCI+AAI: C0-C2 segment.

Can I have AAI without symptoms?

Yes, but symptomatic AAI usually requires treatment due to the impact on neurological and vascular function.

Is surgery always necessary?

No. Early-stage AAI or less severe symptoms may respond to conservative treatment.

Is imaging enough to confirm AAI?

No. AAI diagnosis must include both radiological signs and clinical symptom correlation.

What is the success rate of fusion surgery?

High, when performed at experienced centers with expertise in hypermobility and connective tissue disorders. Preoperative traction test is key in predicting success in each case.

Begin Your Path Toward Recovery

If you suspect AAI or have been experiencing unexplained neurological or autonomic symptoms, our team in Barcelona is here to help. At Promohealth SL, led by Dr. Vicenç Gilete, we offer comprehensive diagnostic evaluations and personalized treatment strategies—from imaging to recovery.