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Atlantoaxial Instability (AAI)

Craniocervical instability and atlantoaxial instability are diagnoses that often cause an immense amount of disability and confusion. Let’s review all of that here to make sure you know what these terms mean, common symptoms of these problems, how these diagnoses are made, and what the treatment options entail. Let’s dig in.

What is Atlanto-Axial Instability (AAI), also known as Craniocervical Instability (CCI)?

CCI stands for craniocervical instability and AAI means atlantoaxial instability. Before we get into what these terms mean, let’s review the anatomy of the craniocervical junction, or where the cervical spine meets the skull.

The upper neck where the spine meets the head is called the craniocervical junction or CCJ. The seven spine bones or vertebrae in your neck are numbered from C1-C7. The skull is numbered as C0. The C0-C2 bones make up the CCJ. In fact, another name for instability in this area is CCJ Instability.

While the lower neck bones have a cushioning disc in the front and two facet joints in the back at each level, the upper neck is built differently.

The C1 bone is called the atlas and the C2 bone has a part that sticks up (dens) that fits into the atlas:

This CCJ area has many ligaments that connect C1 to C2 and C2 to the skull. These main ligaments are:

  • Alar
  • Transverse
  • Accessory

Altogether, the elements outlined here work as a functioning unit to hold the skull onto the neck. This is how those ligaments fit together:

Atlantoaxial instability and craniocervical instability basically mean the same thing – that these ligaments that hold the head onto the neck are damaged, which leads to instability – but refer to different parts of the same functioning unit, the CCJ.

What is Instability and Why Is It a Big Deal?

Instability simply means that bones move around too much, usually due to damaged ligaments. In the spine, this can cause nerves to get banged into and joints to get damaged. In the craniocervical junction, instability can cause the upper cervical spinal nerves to get irritated, leading to headaches. In addition, the C0-C1 and C1-C2 facet joints can also get damaged. In addition, there are other nerves that exit the skull here that can get irritated, like the vagus nerve, which can cause rapid heart rate.

What’s the Difference Between CCI and AAI? CCI refers to instability in any part of the craniocervical junction while AAI refers to instability at C1-C2. The only reason to differentiate them is usually that atlantoaxial instability patients can be treated with a less invasive C1-C2 screw fixation while CCI patients may need more extensive surgery. However, as you’ll see below, surgery is not always the best treatment for these conditions.

What are the Symptoms of AAI?

The symptoms of CCI / AAI include:

  • Headaches
  • Dizziness/Imbalance/Vertigo
  • Visual disturbances
  • Brain fog
  • Rapid heart rate (tachycardia)
  • Random area of numbness or pain or other symptoms such as stomach upset.

Brain Fog

Brain fog is one of the hallmark symptoms of Craniocervical instability. It is characterized by slow thinking, difficulty focusing, confusion, lack of concentration, forgetfulness, or haziness in thought. The severity of symptoms varies from patient to patient. Ever had a bad hangover or high fever and had trouble concentrating or completing simple tasks? This brain fog. Some patients describe it as a generalized haziness in thought as if cotton were stuck in the head. In addition to cognitive impairments, many patients also report generalized mental fatigue making complex tasks almost impossible. The exact cause of brain fog is unknown. Possible explanations include…

Read More About Brain Fog

Cervicalgia / Neck Pain

Cervicalgia is also known as neck pain, which is an all-too-common, unpleasant pain. Read here to learn the symptoms, diagnosis, and treatment options. We will discuss other causes for cervicalgia. What symptoms are associated with cervicalgia? How is cervicalgia diagnosed? What are the treatment options for cervicalgia? Cervicalgia is a medical term used to describe neck pain. It is very common and affects approximately 2/3 of the population at some point in their life. Cervicalgia is the 4th major cause of disability. Risk factors include injury, prior history of neck and musculoskeletal pain, jobs that require a lot of desk work, low social support, job insecurity, physical weakness, and poor computer station setup.

Read More About Cervicalgia / Neck Pain

Chronic Fatigue

Have you ever had a challenging all-day hike, athletic endeavor, or worked a double shift and felt exhausted the next day? Later that day or the next morning, moving across the room may have seemed almost impossible and took herculean power. Now image this occurs on a daily basis without any provocation. 24/7 simple tasks are nearly impossible due to a lack of strength and energy. This is chronic fatigue, and it is one of the common symptoms associated with craniocervical instability. Severity can vary and in severe cases, patients are confined to their beds. Aggravating and alleviating factors often times can not be identified.

Read More About Chronic Fatigue

Chronic Headaches

Do you suffer from chronic headaches? Maybe it’s a daily issue, maybe once a week, maybe even less often, but one thing’s for sure—when a chronic headache kicks in, it can be a real pain in the neck, literally. In order to effectively address chronic headaches, you have to first determine if the pain is caused by a problem in your neck. Let’s take a look at a few neck issues that can cause headaches: Weak neck muscles – The head, on average, weighs about ten pounds, so when the neck muscles are weak, it can make your head feel a bit like a bowling ball that your neck can’t quite balance. There are many muscles that, along with the cervical spine, work together to help support the neck and aid movement…

Read More About Chronic Headaches

Gastrointestinal (GI) Problems

Gastrointestinal (GI) problems can be debilitating comprising one’s wellbeing and ability to confidently engage in life. Symptoms vary and can include nausea, bloating, constipation, diarrhea, delayed motility, abdominal pain, irritable bowel-like symptoms, heartburn, and reflux. GI problems can be due to structural and functional problems within the gut itself. Examples include hiatal hernia and bacterial overgrowth. Less appreciated is the fact that many patients with Craniocervical instability (CCI) can also have significant GI problems. Regrettably, many of these patients undergo extensive, costly GI evaluations only are told that their examinations and studies are normal. This can be extremely frustrating. For these patients…

Read More About Gastrointestinal (GI) Problems

Muscle Pain After Cervical Fusion Surgery

Cervical Fusion is a major surgery that involves joining one or more of the spinal bones together using screws, bolts, and plates (1). The hardware may be placed in the front (anterior) or the back( posterior) of the cervical spine. The disc between the spinal bones is often times removed and replaced with a bone graft or a spacer. The neck of composed of 7 boney building blocks that are numbered from 1-7. The letter C is associated with the numbers to designate the cervical spine. Hence the bones in the neck are C1 through C7. Sandwiched between neck bones are important shock absorbers called discs. A cervical fusion surgery removes…

Read More About Muscle Pain After Cervical Fusion Surgery

Neck Pain and Dizziness

Our body’s balancing system is compromised of three separate systems that work closely together to keep the body in balance: the eyes, inner ear, and upper cervical spine. The upper cervical spine contains and processes information about your position in space and communicates this information to your eyes and inner ears via nerves. There is a constant highway of electrical signals between the cervical spine, inner ear, and eyes that keep us upright, make us aware of our position and enable us to walk, move and run. This balancing system requires the inner ear, eyes and cervical spine to be operational…

Read More About Neck Pain and Dizziness

Pain At The Base Of The Neck And Skull

The base of the skull is a complex area.  It involves the upper cervical spine, facet joints, muscles, tendons, ligaments, and nerves.  Irritation or injury to any one of these structures can result in pain at the base of the skull.  Unfortunately, this area is not understood by many providers.  This can lead to a delay in treatment and unnecessary pain and suffering.Treatment options depend upon the underlying cause of the pain.  Conservative therapy in the form of physical therapy when appropriate is the best first-line treatment.  Steroids are often recommended but should be avoided as they are toxic to orthopedic tissue and have significant side effects…

Read More About Pain At The Base Of The Neck And Skull

Rapid Heart Rate

Rapid heart rate can be debilitating, compromising your wellbeing and ability to complete the easiest of tasks, and, unfortunately, it is a common symptom of craniocervical instability or other upper cervical conditions. Normal resting adult heart rate ranges from 60-85 beats per minute. Tachycardia is a medical term for heart rates of 100 beats per minute. Most of us have experienced rapid heart rates after vigorous exertion or exercise. Remember how your heart was rapidly beating after wind sprints or chasing after your dog who jumped the fence? Your heart is rapidly pounding in your chest. Unfortunately for some patients that is their baseline.

Read More About Rapid Heart Rate

Stiff Neck

Conventional wisdom states that stiff neck symptoms can be treatable with nonsurgical remedies. However, not all stiff neck symptoms are benign, and leaving the stiff neck untreated can lead to a limited range of motion that can affect your overall health and quality of life. A stiff neck can cause pain, tightness, popping, and clicking noises and sensations and affect daily activities. A detailed examination of stiff neck symptoms can determine the exact condition affecting the stiffness of one’s neck. Where does the neck hurt? Neck stiffness can occur at the base of the head, down to the shoulders. This can be associated with pain, crunching noises, or popping sensations and may…

Read More About Stiff Neck


Remember the ringing in your ears after a loud rock concert or highly charged sporting event? It is that ringing or buzzing sound that slowly improves the next day over several hours.  Unfortunately for some individuals, the ringing in the ears is not due to an external event.  Even worse is it does not resolve over time.  This condition is called tinnitus.   It is a medical condition characterized by ringing or other noises in one or both ears NOT caused by an external sound.   Other individuals cannot hear the ringing that patients describe. It is a common problem.  It affects approximately 15-20% of individuals. 

Read More About Tinnitus
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How do you test AAI? (Testing & Diagnosis)

CCI and AAI are often diagnosed via the patient’s symptoms and either a hands-on manual test by the doctor or therapist or diagnostic imaging. However, realize that for many patients, getting the right testing to cinch the diagnosis is difficult. Let’s dive in.

Highly trained upper cervical chiropractors and manual physical therapists can often diagnose CCI by manual techniques. This means that the patient is seeing an upper cervical chiropractic specialist (NUCCA or Atlas-Orthogonal) and the patient gets only temporary relief from manual adjustments. Or if the patient is seeing a manual physical therapist (very specialized PT focused on spine), then specific hands-on diagnostic tests are performed (alar stress test).

There are many different types of imaging that can be performed to help make a diagnosis:

  • Dynamic Motion X-ray (DMX)
  • CT Scan with motion
  • Static Upper Neck MRI
  • Dynamic MRI

Dynamic Motion X-ray (DMX)

This is a real-time x-ray of the neck. The goal is to allow the patient to move and look for how the bones stay aligned or move too much. For more information, see my video below:

CT Scan with Motion

A CT scan is a specialized 3D x-ray and in this case, it’s performed with the patient’s head turned right or left. Excessive motion, usually at C1-C2 can be used to make a diagnosis of CCI.

Static Upper Neck MRI

This test can be performed in two ways. The first is a routine MRI where different measurements can be performed such as:

To learn more about Grabb-Oakes, see my video below:

Powers Ratio:

Dynamic MRI

MRIs are usually performed with the patient lying very still, face-up in a tube, but they can also be performed with the patient sitting with movement. This can be used to see if the upper neck bones move too much with motion.

How is Atlantoaxial Instability Treated?

There are three main types of treatment:

  • Conservative Care-Chiropractic and PT
  • Injections
  • Surgery

Conservative Care

There are two major disciplines in chiropractic which are NUCCA (National Upper Cervical Chiropractic Association) and AO (Atlas-Orthogonal). These generally involve measuring the angles of the upper neck bones on x-ray and then specific manipulations to get them back in place. Patients who only get temporary relief are then more likely to be chronically unstable. There are also highly trained physical therapists and osteopaths who specialize in the upper neck. These providers can also offer manipulative care with the same caveats as above.


There are a number of different types of injections here which include:

  • Intra-articular facet injections
  • Posterior prolotherapy
  • PICL procedure

Intra-articular facet injections of the upper cervical facet joints are highly specific and difficult to perform. These are joints in the neck that can get beat up or damaged when there is CCI or AAI (AAI impacting C1-C2). There are only a handful of physicians in the United States with much experience in injecting these joints using x-ray guidance and contrast to ensure placement. These joints can be injected with substances like PRP or bone marrow concentrate, which can help to reduce the pain or heal the damage.

Posterior prolotherapy involves injecting the ligaments in the back of the neck (not the alar, transverse, or accessory ligaments). While this can help patients with CCI or AAI, regrettably, in our experience, most patients don’t get relief with posterior prolotherapy.

The PICL procedure involves direct injection of the ligaments that hold the head on (alar, transverse, or accessory ligaments) from the front. This is a highly complex procedure that involves endoscopy for direct visualization of the back of the throat area, specialized anesthesia, a specialized mouth piece, and x-ray guidance. In our experience, this procedure can help many patients avoid the need for neck fusion. See our video below for more information:


The surgical approach here involves fusion, which means that the doctor inserts screws and plates to fuse various parts of the upper cervical bones. These are all higher-risk procedures than a routine mid or lower cervical fusion.  Here are the main surgeries:

  • C1-C2 screw fixation
  • C0-C2 fusion (Goel and Harms Technique)
  • Occipital-cervical Fusion (Skull Base to C2)

C1-C2 screw fixation is likely the most common procedure we see. This involves placing a screw across the C1-C2 joint and is involved in atlantoaxial instability (AAI). The main problems have been:

  • Lack of fusion of the C1-C2 joint. If this joint doesn’t fuse (grow together with bone), the joint is now destroyed due to the surgery and cause pain. In that case a repeat procedure may need to be performed.
  • Sacrifice of the occipital nerve. This is the nerve that goes up to your head, so injury to this nerve causes chronic headaches.
  • Misplacement of screws. The most common thing we see is that the screw is placed too deep and into the C0-C1 joint which leads to arthritis in that joint.

A C0-C2 fusion is when the doctor inserts screws into the vertebral bodies instead of across the joint itself. This is a bigger procedure than C1-C2 screw fixation. It has many of the same possible complications including lack of fusion and injury to the nerve.

An occipital-cervical fusion involves extending the hardware up to the skull base. This is the largest of the three surgeries. It has all of the same possible complications, which are generally highest for this procedure since it’s the most invasive.

Cervical Fusion

Cervical Fusion is often recommended when chronic neck pain problems worsen over time. What exactly is it? Cervical Fusion is a major surgery that involves joining one or more of the spinal bones together using screws, bolts, and plates (1). The hardware may be placed in the front (anterior) or the back( posterior) of the Cervical spine. The disc between the spinal bones is often times removed and replaced with a bone graft or a spacer. The neck of composed of 7 boney building blocks that are numbered from 1-7. The letter C is associated with the numbers to designate the Cervical Spine.

Read More About Cervical Fusion


The other day I was evaluating a patient and reviewing the treatment options for their spine condition.  After discussing prior treatments, we got to the topic of medications taken for pain relief. She explained that she mainly utilized anti-inflammatory (NSAID) medications and then she told me to hold much she takes and has been for many years…..she takes close to 2 grams (2000 milligrams) on a daily basis which equated to about 9-10 capsules of medication per day.  I was shocked, considering she was pre-diabetic and with high blood pressure plus the kicker of it is that her PCP (primary care physician) is ok with this…

Read More About NSAIDs

Occipital Cervical Fusion

An Occipital Cervical Fusion also known as Occipitocervical Susion is a Major Surgery. It is not a routine operation and is a challenging procedure due to complex anatomy of the upper neck. The procedure involves rods, plates and screws that are placed into the Cervical Spine and Occiput. A plate secured by screws are placed at the base of the Occiput. Screws are also placed into one or more Cervical bones. Rods then connect the Occipital plate to the Cervical screws as shown below. The goal of Occipital Cervical Surgery is a boney fusion between the skull and neck and to relieve…

Read More About Occipital Cervical Fusion

PICL Procedure

CCI stands for cranial cervical instability which means that the ligaments that hold the head on are too loose. To help that problem, we developed a new procedure called PICL which stands for Percutaneous Implantation of the CCJ Ligaments. This is still an investigational procedure that has already changed many lives and helped patients avoid a complication-laden upper cervical fusion. Given the interest in the PICL procedure from patients who have CCI, there are lots of questions. Since the procedure isn’t yet covered by insurance, a few have asked why it costs more than their co-pay and deductible if they decide to have a more invasive cervical fusion.

Read More About PICL Procedure
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Our Doctors Who Treat AAI

Christopher J. Centeno, MD

Christopher J. Centeno, M.D. is an international expert and specialist in Interventional Orthopedics and the clinical use of bone marrow concentrate in orthopedics. He is board-certified in physical medicine and rehabilitation with a subspecialty of pain medicine through The American Board of Physical Medicine and Rehabilitation. Dr. Centeno is one of the few physicians in the world with extensive experience in the culture expansion of and clinical use of adult bone marrow concentrate to treat orthopedic injuries. His clinic incorporates a variety of revolutionary pain management techniques to bring its broad patient base relief and results. Dr. Centeno treats patients from all over the US who…

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John Schultz, MD

My passion and specialization are in the evaluation and treatment of cervical disc, facet, ligament and nerve pain, including the non-surgical treatment of Craniocervical instability (CCI). I quit a successful career in anesthesia and traditional pain management to pursue and advance the use of PRP and bone marrow concentrate for common orthopedic conditions. I have been a patient with severe pain and know firsthand the limitations of traditional orthopedic surgery. I am a co-founder of the Centeno-Schultz Clinic which was established in 2005. Being active is a central part of my life as I enjoy time skiing, biking, hiking, sailing with my family and 9 grandchildren.

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Other Resources for AAI

  • New Interventional Orthopedics Atlas

    Writing a textbook is an enormous undertaking.  In creating a first of its kind, comprehensive textbook in Interventional Orthopedic Procedures, authors Williams, Sussman and Pitts have established a new benchmark in the field.  Congratulations to its authors for their dedication, foresight and commitment to the advancement of Interventional Orthopedics.  What Is Interventional Orthopedics?  Interventional Orthopedics … Continued

  • Understanding Cervical Spine Instability Measurements

    Cervical Spine Instability Measurements: How To Precisely Interpret Them It was all a blur. You were waiting for the red light to change when a large truck slammed into your vehicle. You did not see the approaching vehicle but heard the skidding tires.  The brain fog, dizziness, and fatigue have not responded to conservative therapy.  … Continued

  • What Is the Atlantodens Interval? A QuickStart Guide

    The headaches and dizziness became progressive in nature and responsive to conservative care. Chiropractic adjustments provided only  transient relief as you could not maintain your adjustment.  A surgeon reviewed your history, symptoms and radiographic studies.  He mentioned different measurements that were abnormal.  What is the Atlantodens Interval? What is the Atlas?  What is the Axis … Continued

  • Your Grabb Oakes Measurement: What Does It Mean?

    The headaches, brainfog and balance problems has been progressive in nature and unresponsive to conservative care. After what seemed like endless consultations and examinations your chiropractor believes it is Craniocervical Instability.  During a surgical evaluation the MRI was reviewed, and different measurements were taken all of which was confusing. What is the Cranium? What is … Continued

  • Craniocervical Instability & Ehlers Danlos Syndrome: Know the Facts

    Gymnastics and yoga were easy as you were super flexible.  With continued training your shoulders and knees kept popping out of place.  A series of small but significant traumas left you sidelined both from athletics, academics and socially.  Brain fog and fatigue were common themes.  You have seen countless physicians with conflicting information.  Your chiropractor … Continued

  • What Are the Long Term Effects of Untreated Whiplash?

    You were waiting for the red light to change when you heard the brakes screeching. Out of nowhere a large SUV rear ends you and pushes your vehicle into the intersection.  Your neck and shoulder hurt and you’re not processing all the information.  Your doctor thinks you have Whiplash.  What is Whiplash?  What are the … Continued

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