C1-C2 Atlantoaxial Joint: What This Upper Neck Finding Means on MRI

Name: C1-C2 Atlantoaxial Joint: What This Upper Neck Finding Means on MRI
Creator: Ifije Ohiorhenuan, MD, PhD

Written by Ifije Ohiorhenuan, MD, PhD — Board-Certified Spine Surgeon. Last updated 2026-06-20.

C1-C2 is the joint between the top two bones in your neck, and it is especially important because it allows much of your head rotation while sitting close to the spinal cord.

If your MRI report mentions “C1-C2,” “atlantoaxial,” “dens,” “odontoid,” “subluxation,” or “instability,” it is normal to feel worried. These words sound serious. Sometimes they are important. Many times, they need context.

MRI means magnetic resonance imaging. It is a scan that shows the spinal cord, nerves, discs, ligaments, and soft tissues. CT means computed tomography. It is a scan that shows bone detail very well.

This article explains what the C1-C2 atlantoaxial joint is, why it appears on imaging reports, when it may explain symptoms, and when it needs more urgent attention.

What Is the C1-C2 Atlantoaxial Joint?

C1 and C2 are the top two vertebrae in your neck. A vertebra is one of the bones that makes up the spine.

C1 is called the atlas. It is the top neck bone. It supports the skull.

C2 is called the axis. It is the second neck bone.

The atlantoaxial joint is the joint between C1 and C2. “Atlantoaxial” simply means atlas-to-axis.

The dens, also called the odontoid process, is a peg-like part of C2. C1 rotates around this peg. This is one reason you can turn your head side to side.

In my practice, I explain C1-C2 as the swivel joint of the neck. It lets you turn your head side to side, but it also sits in a very important location near the spinal cord.

The spinal cord is the main nerve pathway that carries signals between your brain and body. At C1-C2, the spinal cord passes just behind the dens.

C1-C2 is different from lower neck levels such as C5-C6 or C6-C7. Most lower cervical levels have a disc between the bones. A disc is a cushion between two vertebrae. C1-C2 does not have a typical disc between the bones.

Unlike many other spinal levels, C1-C2 is less about a disc and more about a specialized rotating joint.

Why C1-C2 Shows Up on MRI or CT Reports

C1-C2 may show up on an MRI or CT report for several reasons. Some findings are mild. Some are more important.

Common report phrases include:

C1-C2 degenerative change: “Degenerative” means wear-and-tear change. This can include arthritis.
Atlantoaxial arthritis: Arthritis means joint wear, irritation, or inflammation.
Odontoid or dens changes: These are changes around the peg-like part of C2.
C1-C2 joint effusion: An effusion is extra fluid in or near a joint.
Pannus or retro-odontoid tissue: Pannus means thickened soft tissue. Retro-odontoid means behind the dens.
Subluxation: Subluxation means partial shifting or abnormal alignment of a joint.
Atlantoaxial instability: Instability means abnormal movement or alignment between C1 and C2.
Spinal cord compression at the craniocervical junction: Spinal cord compression means pressure on the spinal cord. The craniocervical junction is the area where the skull meets the upper neck.

MRI and CT often show anatomy and wear-and-tear changes. The key question is not just, “Is something listed?” The key question is, “Does it match your symptoms, and does it affect the spinal cord or stability?”

What I look for on MRI is not just the phrase “degenerative change,” but whether there is pressure on the spinal cord, abnormal alignment, or a soft-tissue process around the dens.

CT can be very helpful for bone detail. It may show arthritis, erosions, fractures, or alignment. An erosion is an area where bone has been worn away.

MRI is often better for the spinal cord, ligaments, and soft tissue. A ligament is a strong band of tissue that helps hold bones in place.

What Symptoms Can Come From C1-C2 Problems?

C1-C2 problems can be linked with symptoms in some people.

Possible symptoms include:

Pain high in the neck
Pain at the base of the skull
Occipital headaches, which are headaches felt in the back of the head
Pain when turning the head
Neck stiffness
Reduced ability to rotate the head

But this part is important: headaches have many causes. Neck pain also has many causes. Many people have more than one neck finding on MRI.

A C1-C2 finding on imaging does not automatically prove that C1-C2 is the pain generator. A pain generator is the structure that is actually causing the pain.

The MRI finding matters most when it lines up with the patient’s symptoms, exam, and sometimes additional imaging.

In my practice, the finding matters most when the location of pain, the physical exam, and the imaging all point in the same direction.

For example, C1-C2 arthritis may matter more when the pain is very high in the neck, worse with rotation, and the imaging shows clear joint wear on the same side as the pain. Even then, the finding still needs careful clinical review.

Lower neck problems can also cause neck pain, arm pain, numbness, or weakness. Common lower cervical levels include the C5-C6 cervical segment and the C6-C7 cervical segment. A cervical disc herniation, which means a disc bulge or rupture pressing on nearby nerves, is more common at these lower levels than at C1-C2.

What Is Atlantoaxial Instability?

Atlantoaxial instability means abnormal movement or alignment between C1 and C2.

The word sounds alarming. Sometimes it is serious. Sometimes it is a chronic finding that needs careful tracking. The meaning depends on the cause, the amount of movement, your symptoms, and whether the spinal cord is affected.

C1 and C2 are held in position by joints and ligaments. Some of these ligaments help keep the dens in the right position in front of the spinal cord. If those supports are damaged or weakened, C1 and C2 may move too much or line up poorly.

Atlantoaxial instability can occur with:

Trauma, such as a fall, car crash, or sports injury
Rheumatoid arthritis, which is an inflammatory disease that can attack joints
Congenital conditions, which are conditions present from birth
Down syndrome, a genetic condition linked with higher risk of upper neck instability
Ligament injury
Infection
Tumor
Prior cervical surgery
Severe degeneration, meaning advanced wear-and-tear change

When I see the word “instability,” I want to know whether this is a stable chronic finding, a trauma-related problem, or something that is affecting the spinal cord.

Doctors may look at several imaging details:

The alignment of C1 and C2
The space available for the spinal cord
The relationship of the dens to the front arch of C1
Whether the spinal cord is compressed
Whether the spinal cord has signal change, which can mean irritation or injury seen on MRI
Whether there is fracture, erosion, pannus, infection, or tumor

Sometimes doctors use flexion-extension X-rays. These are X-rays taken while the neck bends forward and backward. They may help show abnormal motion, but only when this is safe and appropriate.

CT may be better for bone detail. MRI may be better for the spinal cord, ligaments, and soft tissue around the dens.

When C1-C2 Findings Are More Concerning

Some C1-C2 findings need faster evaluation. This is especially true when symptoms suggest pressure on the spinal cord or when the finding happened after trauma.

More concerning situations include:

Recent trauma or fall with upper neck pain
Weakness in the arms or legs
Numbness that is new, spreading, or linked with weakness
Clumsiness or loss of hand coordination
Trouble walking or new imbalance
Bowel or bladder control changes
Fever with severe neck pain
MRI report mentions spinal cord compression
MRI report mentions cord signal change
Report mentions severe stenosis, which means severe narrowing around the spinal cord or nerves
Report mentions instability, fracture, dislocation, tumor, or infection
Known rheumatoid arthritis
Known Down syndrome
Known connective tissue disorder, which is a condition that affects ligaments, joints, or other support tissues
Prior cervical surgery
Progressive symptoms, meaning symptoms are getting worse over time

If you have new weakness, trouble walking, loss of coordination, bowel or bladder changes, fever with severe neck pain, or severe neck pain after trauma, seek urgent medical evaluation. SpineClarity’s written MRI review is not emergency care.

Spinal cord compression in the neck can cause cervical myelopathy. Cervical means neck. Myelopathy means symptoms from pressure or injury to the spinal cord. You can read more about spinal cord compression and cervical myelopathy.

How Doctors Think Through a C1-C2 MRI Finding

A C1-C2 MRI finding is not interpreted in isolation. A spine surgeon usually asks a series of questions.

Is the C1-C2 finding actually related to your symptoms?

This is the first question. If your pain is low in the neck and travels down the arm, C1-C2 may not be the main issue. Lower cervical levels may be more relevant.

If your pain is high in the neck, worse with turning, and near the base of the skull, C1-C2 may deserve closer attention.

Is the spinal cord compressed?

This is one of the most important questions. The spinal cord sits close to the dens. If there is pressure on the cord, the finding may be more serious.

Symptoms such as hand clumsiness, balance trouble, weakness, numbness, or walking difficulty raise concern for spinal cord involvement.

Is there abnormal motion or instability?

Some imaging shows a static picture. It shows one position in time. If instability is suspected, doctors may consider other imaging, such as flexion-extension X-rays, when safe.

Is there a high-risk cause?

C1-C2 findings can have different causes. These include arthritis, trauma, inflammatory disease, infection, tumor, congenital anatomy, or prior surgery.

The cause matters because treatment pathways are very different.

Are lower cervical levels also abnormal?

C5-C6 and C6-C7 more commonly involve disc degeneration and nerve root compression. A nerve root is a nerve branch that exits the spine and travels into the arm.

C1-C2 is more specialized. It often involves rotation, joints, ligaments, and the dens.

Nearby levels can also matter. The nearby upper cervical segments, such as C2-C3 and C3-C4, may also contribute to upper neck pain in some cases.

Common Treatment Categories for C1-C2 Problems

Treatment depends on the cause of the C1-C2 finding, the patient’s symptoms, exam, and the degree of instability or cord involvement.

In my practice, surgery is not based on the MRI wording alone. The decision depends on symptoms, neurologic function, alignment, motion, and the underlying cause.

Common treatment categories include:

Observation and monitoring

Some C1-C2 findings are watched over time. This may be considered when symptoms are mild, stable, and there is no clear spinal cord compression or dangerous instability.

Physical therapy

Physical therapy may focus on safe motion, posture, and strengthening. At C1-C2, therapy decisions should respect the special anatomy of the upper neck.

Medications

Medications may be used for pain or inflammation when appropriate. This category can include anti-inflammatory medicines, nerve pain medicines, or other pain treatments depending on the situation.

Image-guided injections

In selected cases, injections may be considered. Image-guided means the doctor uses X-ray or CT guidance to place the needle more accurately. These may be used for pain diagnosis or pain relief in specific cases.

Workup for inflammatory or systemic causes

If there is concern for rheumatoid arthritis, infection, tumor, or another systemic cause, additional testing may be needed. Systemic means it affects the body as a whole, not just one joint.

Bracing

A brace may be used in select cases. Bracing decisions depend on the cause, stability, symptoms, and imaging.

Surgery

Surgery may be considered in selected cases involving:

Instability
Spinal cord compression
Progressive neurologic symptoms
Fracture
Deformity
Tumor
Infection
Severe pain that has a clear structural source and has not improved with other care

This does not mean every C1-C2 finding needs surgery. Many do not. The MRI wording is only one part of the decision.

When a Written MRI Review May Help

If your MRI or CT report mentions C1-C2, the dens, atlantoaxial arthritis, subluxation, or instability, it can be hard to know how much the finding matters. SpineClarity offers a written MRI/case review from a board-certified spine surgeon. You can upload your symptoms, imaging report, and relevant records, and receive a plain-language written interpretation with a suggested next-step category. This is not emergency care and does not replace an in-person physician relationship.

Frequently Asked Questions

What does C1-C2 mean on my MRI report?

C1-C2 means the joint between the top two bones in your neck. C1 is the atlas. C2 is the axis. This area helps your head turn side to side and sits close to the spinal cord.

Is C1-C2 the same as the atlantoaxial joint?

Yes. The atlantoaxial joint is the medical name for the C1-C2 joint. “Atlanto” refers to the atlas, or C1. “Axial” refers to the axis, or C2.

Can C1-C2 arthritis cause headaches?

C1-C2 arthritis can be associated with headaches at the back of the head in selected patients. These are often called occipital headaches. But headaches have many causes. A C1-C2 arthritis finding on MRI or CT does not automatically prove it is the cause.

What is atlantoaxial instability?

Atlantoaxial instability means abnormal movement or alignment between C1 and C2. It may involve the ligaments that help hold the dens and C1 ring in the right position.

Is atlantoaxial instability dangerous?

It can be, but not always. The seriousness depends on the cause, the amount of movement, whether there was trauma, whether symptoms are getting worse, and whether the spinal cord is compressed.

Does a C1-C2 finding mean I need surgery?

No. A C1-C2 finding does not automatically mean you need surgery. Treatment depends on symptoms, neurologic findings, imaging severity, stability, and the cause of the finding.

What is the dens or odontoid process?

The dens, also called the odontoid process, is a peg-like part of C2. C1 rotates around it when you turn your head side to side.

Why would my doctor order flexion-extension X-rays?

Flexion-extension X-rays are bending X-rays. They show the neck in forward and backward positions. In selected cases, they may help assess abnormal motion or instability. They are used only when safe and appropriate.

Can lower neck problems cause similar symptoms?

Yes. Lower neck problems can also cause neck pain, headaches, arm pain, numbness, or weakness. Levels like C5-C6 and C6-C7 more often involve disc degeneration or nerve root compression.

When should I seek urgent care for a C1-C2 finding?

References

American College of Radiology. ACR Appropriateness Criteria® Acute Spinal Trauma. Journal of the American College of Radiology.
American College of Radiology. ACR Appropriateness Criteria® Cervical Neck Pain or Cervical Radiculopathy.
Berbari EF, Kanj SS, Kowalski TJ, et al. 2015 Infectious Diseases Society of America Clinical Practice Guidelines for the Diagnosis and Treatment of Native Vertebral Osteomyelitis in Adults. Clinical Infectious Diseases. 2015;61(6):e26-e46.
Bogduk N, Govind J. Cervicogenic headache: an assessment of the evidence on clinical diagnosis, invasive tests, and treatment. Lancet Neurology. 2009;8(10):959-968.
Bull MJ; Committee on Genetics. Health supervision for children with Down syndrome. Pediatrics. 2011;128(2):393-406.
Davies BM, Mowforth OD, Smith EK, Kotter MRN. Degenerative cervical myelopathy. BMJ. 2018;360:k186.
Fehlings MG, Tetreault LA, Riew KD, Middleton JW, Wang JC, eds. A Clinical Practice Guideline for the Management of Patients With Degenerative Cervical Myelopathy. Global Spine Journal. 2017;7(3 Suppl).
Headache Classification Committee of the International Headache Society. The International Classification of Headache Disorders, 3rd edition. Cephalalgia. 2018;38(1):1-211.
Joaquim AF, Appenzeller S. Cervical spine involvement in rheumatoid arthritis—A systematic review. Autoimmunity Reviews. 2014;13(12):1195-1202.
Schaeren S, Jeanneret B. Atlantoaxial osteoarthritis: case series and review of the literature. European Spine Journal. 2005;14(5):501-506.
Star MJ, Curd JG, Thorne RP. Atlantoaxial lateral mass osteoarthritis: a frequently overlooked cause of severe occipitocervical pain. Spine. 1992;17(6 Suppl):S71-S76.
StatPearls. Anatomy, Head and Neck: Atlantoaxial Joint. NCBI Bookshelf. StatPearls Publishing.
Yang SY, Boniello AJ, Poorman CE, Chang AL, Wang S, Passias PG. Atlantoaxial Instability. StatPearls. NCBI Bookshelf. StatPearls Publishing.