What is the Craniocervical Junction?

The craniocervical junction (CCJ) is the area where the base of the skull and the upper cervical vertebrae (C0–C1–C2) meet. This zone ensures the mobility of the head, protects the brainstem, and important blood vessels and nerves pass through it.

However, due to trauma, poor posture, joint degeneration, autoimmune disease, or connective tissue weakness, it can become unstable, which can cause various symptoms.

Why can the CCJ Become Unstable?

The CCJ is the most mobile part of the neck. The atlanto-occipital (AO) and atlantoaxial (AA) joints are located here, which enable flexion and extension of the head, lateral bending, and rotation.

The ligaments in the central part—such as the alar, apical, cruciform, etc.—hold the dens (odontoid process of C2) in a stable position so that it does not move toward the spinal cord.

Instability occurs when these ligaments become loose or injured. This can happen suddenly (e.g. in a car accident, even at low speed, <20 km/h), or gradually (due to repeated poor posture, e.g. prolonged slouching in front of a computer).

Risk factors: female sex, thin and long neck, low headrest position in a car during an accident, autoimmune disease (e.g. rheumatoid arthritis), or genetic causes (e.g. Ehlers–Danlos syndrome).

If the ligaments are lax, the joints become hypermobile—this is called microinstability. In this case, the muscles compensate, which leads to muscle spasm, pain, nerve entrapment (e.g. occipital nerve), and later degeneration (osteoarthritis). In the long term, nerve inflammation or spinal canal narrowing may also develop.

How Do We Diagnose Craniocervical Instability?

The diagnosis of craniocervical instability (CCI) is mainly based on the patient’s medical history and symptoms, because these provide the most important information. For example, it is important whether there was an accident or trauma, or whether the symptoms developed gradually, such as neck pain, headache, dizziness, or fatigue. Certain antibiotics may also contribute to ligament damage.

During the physical examination, we assess the movement of the neck, muscle tension, painful points, and possible neurological involvement (e.g. numbness, weakness).

Imaging studies such as conventional X-ray, MRI, or CT play a smaller role, because they do not always show instability. These are mainly used to exclude other diseases, such as tumor or fracture, but their sensitivity and specificity are not perfect, therefore they must always be evaluated together with the symptoms.

Dynamic examinations (e.g. flexion–extension, rotational MRI, CT, or DMX) are increasingly used, as both physicians and patients strive for a precise diagnosis. However, it is important to know that there is no full agreement among experts regarding these measurements.

There are clear cases where the diagnosis of CCI is confirmed, but it cannot always be completely ruled out. Dynamic examinations (e.g. flexion–extension, rotational MRI, CT, or DMX) may help, but only to a limited extent.

Diagnostic Options at Our Clinic

Our clinic also collaborates with a radiology team. Within this framework, dynamic MRI examination and radiological evaluation are available.

At our clinic, we perform functional cervical spine examinations in neutral, flexed, extended, and lateral bending positions, providing diagnostic information similar to Digital Motion X-ray (DMX).

This examination includes capturing static fluoroscopic images of the cervical spine in neutral, mid-range, and end-range positions. These specific positions usually provide sufficient data to assess cervical instability, such as C1–C2 overhang or abnormal displacement, with significantly lower radiation exposure compared to continuous DMX.

A continuous DMX examination (video, 2–3 minutes) has an estimated effective dose of 0.9–5.4 mSv, whereas taking 10 static fluoroscopic images (as described above) results in a significantly lower dose of 0.015–0.09 mSv, which is approximately 1–10% of the DMX dose, due to the reduced exposure time (approximately 3 seconds compared to 180 seconds).

Nevertheless, the diagnosis of non-surgical CCI currently relies much more on medical history and physical examination than on imaging, as there is insufficient data to clearly define the boundary between normal and pathological findings.

More details on imaging

What Does “Microinstability” Mean in the Upper Cervical Spine?

Ligament laxity in the uppermost part of the neck—especially where the skull meets the first two cervical vertebrae (craniocervical junction, CCJ)—can make this region more mobile than normal, without showing a clear fracture or major dislocation/subluxation.

Classic radiographic “red flag” measurements—ADI, BAI, BDI, Powers ratio—are effective in detecting obvious instability, but may miss subtle soft tissue (“discoligamentous”) injuries. In some cases, certain abnormalities only become visible later¹⁴.

What MRI and CT Can and Cannot Show?

MRI:

Best suited for evaluating ligaments and other soft tissues. It can demonstrate structural integrity and detect edema, which may indicate irritation, inflammation, or injury. Commonly used sequences include proton density, T1 3D VIBE, and STIR¹⁰,¹³.

Several studies have found signs suggestive of edema in key CCJ ligaments (alar and transverse ligaments) more frequently after whiplash injury than in healthy individuals²,⁵.

However, this is not always clear-cut. A prospective study found even more such findings in patients with chronic neck pain (not necessarily due to whiplash), and these did not change over a one-year period—suggesting that such signals do not always indicate acute trauma⁸. This may also be due to chronic overload-related instability, but in such cases, establishing the diagnosis is more complex.

CT:

Excellent for assessing bone structures. Measurements such as the lateral atlantodental interval (LADI) can be performed.

However, abnormalities do not always have clinical significance, as similar findings are often seen in asymptomatic individuals as normal anatomical variation, which may lead to overtreatment⁴.

Why Certain Measurements Can be Misleading?

Standard X-rays are two-dimensional. Overlapping anatomical structures may create apparent abnormalities.

Example: on an open-mouth (odontoid) view, the atlas may appear shifted simply due to slight head rotation.

Population-based studies have shown that several findings traditionally considered pathological may also be present in healthy individuals, such as asymmetric LADI or apparent lateral displacement of the atlas (C1) relative to the axis (C2), often caused by head positioning rather than trauma³,⁶.

Key point: normal and pathological ranges overlap, therefore clinical context is essential.

Findings From More Recent Studies

According to the classic rule, in C1 fractures (Jefferson fractures), if the combined lateral displacement of C1 exceeds 7 mm on open-mouth radiographs, rupture of the transverse atlantal ligament (TAL) is assumed.

More recent studies suggest that TAL injury may occur at much smaller displacements. Cadaver studies have identified TAL rupture at around 3 mm¹¹. In CT-based flexion models, increases in ADI following TAL injury were found to be more sensitive than lateral displacement measurements¹⁵.

Relying solely on the traditional rule may therefore result in missed injuries⁷.

Some accepted threshold values (e.g., ADI, BDI) may be too broad compared to CT-based measurements and modern normative data⁹.

Functional Studies: How Much Do Cervical Vertebrae Move?

Classic studies have defined segmental ranges of motion using flexion-extension X-rays and have shown that routine imaging may underestimate instability after whiplash injury¹².

Videofluoroscopy (DMX) allows real-time tracking of small angular and translational movements, demonstrating that subtle but clinically relevant translations do exist¹.

Warning: dynamic imaging results depend heavily on technique, positioning, and interpretation. Variability between evaluators can be significant.

Practical Take-home Messages for Patients

  • There is no single test that can definitively confirm or exclude subtle CCJ instability

  • MRI is useful for assessing ligament condition, but edema does not always indicate an acute tear

  • CT and X-ray measurements are valuable, but some “abnormal” findings may be present in healthy individuals

  • Dynamic imaging (flexion-extension X-ray, dynamic CT/MRI, DMX) may reveal microinstability, but results must be interpreted with caution

  • The most reliable approach is to evaluate imaging findings together with symptoms and physical examination—avoiding both under- and overtreatment

Source:

  1. Wu, Shyi-Kuen, Li-Chieh Kuo, Haw-Chang H. Lan, Sen-Wei Tsai, Chiung-Ling Chen, and Fong-Chin Su. ‘The Quantitative Measurements of the Intervertebral Angulation and Translation during Cervical Flexion and Extension’. European Spine Journal 16, no. 9 (2007): 1435–44. https://doi.org/10.1007/s00586-007-0372-4.
  2. Krakenes, J., B. Kaale, G. Moen, H. Nordli, N. Gilhus, and J. Rorvik. ‘MRI Assessment of the Alar Ligaments in the Late Stage of Whiplash Injury – a Study of Structural Abnormalities and Observer Agreement’. Neuroradiology 44, no. 7 (2002): 617–24. https://doi.org/10.1007/s00234-002-0799-6.
  3. Guenkel, S., M. J. Scheyerer, G. Osterhoff, G. A. Wanner, H. P. Simmen, and C. M. L. Werner. ‘It Is the Lateral Head Tilt, Not Head Rotation, Causing an Asymmetry of the Odontoid-Lateral Mass Interspace’. European Journal of Trauma and Emergency Surgery 42, no. 6 (2016): 749–54. https://doi.org/10.1007/s00068-015-0602-0.
  4. Endler, Christoph H., Daniel Ginzburg, Alexander Isaak, et al. ‘Diagnostic Benefit of MRI for Exclusion of Ligamentous Injury in Patients with Lateral Atlantodental Interval Asymmetry at Initial Trauma CT’. Radiology 300, no. 3 (2021): 633–40. https://doi.org/10.1148/radiol.2021204187.
  5. Krakenes, Jostein, and Bertel R. Kaale. ‘Magnetic Resonance Imaging Assessment of Craniovertebral Ligaments and Membranes After Whiplash Trauma’: Spine 31, no. 24 (2006): 2820–26. https://doi.org/10.1097/01.brs.0000245871.15696.1f.
  6. Chen, Yuchun, Zerui Zhuang, Weili Qi, et al. ‘A Three-Dimensional Study of the Atlantodental Interval in a Normal Chinese Population Using Reformatted Computed Tomography’. Surgical and Radiologic Anatomy 33, no. 9 (2011): 801–6. https://doi.org/10.1007/s00276-011-0817-7.
  7. Park, Heui-Jeon, Dong-Gune Chang, Jong-Beom Park, et al. ‘Radiologic Criteria to Predict Injury of the Transverse Atlantal Ligament in Unilateral Sagittal Split Fractures of the C1 Lateral Mass’. Medicine 98, no. 36 (2019): e17077. https://doi.org/10.1097/MD.0000000000017077.
  8. Vetti, N., J. Kråkenes, T. Ask, et al. ‘Follow-Up MR Imaging of the Alar and Transverse Ligaments after Whiplash Injury: A Prospective Controlled Study’. American Journal of Neuroradiology 32, no. 10 (2011): 1836–41. https://doi.org/10.3174/ajnr.A2636.
  9. Rojas, C. A., J. C. Bertozzi, C. R. Martinez, and J. Whitlow. ‘Reassessment of the Craniocervical Junction: Normal Values on CT’. American Journal of Neuroradiology 28, no. 9 (2007): 1819–23. https://doi.org/10.3174/ajnr.A0660.
  10. Ulbrich, Erika Jasmin, Sandra Eigenheer, Chris Boesch, et al. ‘Alterations of the Transverse Ligament: An MRI Study Comparing Patients With Acute Whiplash and Matched Control Subjects’. American Journal of Roentgenology 197, no. 4 (2011): 961–67. https://doi.org/10.2214/AJR.10.6321.
  11. Woods, Rafeek O., Serkan Inceoglu, Yusuf T. Akpolat, Wayne K. Cheng, Brice Jabo, and Olumide Danisa. ‘C1 Lateral Mass Displacement and Transverse Atlantal Ligament Failure in Jefferson’s Fracture: A Biomechanical Study of the “Rule of Spence”’. Neurosurgery 82, no. 2 (2018): 226–31. https://doi.org/10.1093/neuros/nyx194.
  12. Dvorak, J., D. Froehlich, L. Penning, H. Baumgartner, and M. M. Panjabi. ‘Functional Radiographic Diagnosis of the Cervical Spine: Flexion/Extension’. Spine 13, no. 7 (1988): 748.
  13. Mantripragada, Sravanthi, Anbalagan Kannivelu, and Wilfred Cg Peh. ‘Magnetic Resonance Imaging of Cervical Ligamentous Anatomy and Traumatic Ligamentous Injuries’. Journal of Medical Imaging and Radiation Oncology 64, no. 3 (2020): 368–76. https://doi.org/10.1111/1754-9485.13016.
  14. Mayer, M., J. Zenner, A. Auffarth, et al. ‘Hidden Discoligamentous Instability in Cervical Spine Injuries: Can Quantitative Motion Analysis Improve Detection?’ European Spine Journal 22, no. 10 (2013): 2219–27. https://doi.org/10.1007/s00586-013-2854-x.
  15. Perez-Orribo, Luis, Laura A. Snyder, Samuel Kalb, et al. ‘Comparison of CT versus MRI Measurements of Transverse Atlantal Ligament Integrity in Craniovertebral Junction Injuries. Part 1: A Clinical Study’. Journal of Neurosurgery: Spine 24, no. 6 (2016): 897–902. https://doi.org/10.3171/2015.9.SPINE13808.

What Symptoms Can Craniocervical Instability (CCI) Cause?

Symptoms can be varied and may sometimes resemble other conditions, such as fibromyalgia or vestibular (dizziness-related) disorders.

Common Symptoms:

  • Headache in the occipital region, radiating to the forehead, behind the eyes, or into the ear (cervicogenic headache, often unilateral, sharp or throbbing)

  • Neck pain, stiffness, muscle tension (e.g. in the neck and shoulder muscles), shoulder pain

  • Dizziness, tinnitus, blurred vision, “brain fog” (difficulty concentrating, forgetfulness)

  • Fatigue, widespread pain similar to fibromyalgia

  • Other complaints: palpitations, digestive problems, hot flashes, nausea (possible involvement of the vagus nerve)

In More Severe Cases:

  • Difficulty holding the head upright

  • Transient weakness or numbness affecting the whole body

  • Rarely: eye movement disturbances or tongue deviation

Symptoms are often caused by ligament laxity in the cervical spine, which leads to microinstability. Over time, this condition may result in muscle spasms, headaches, and nerve irritation.

What Treatment Options are Available for CCI?

Also known as PICL treatment, which addresses both posterior and anterior ligaments and joints:

  • Mild instability (WAD 0) typically responds well to physiotherapy and may resolve spontaneously

  • Severe craniocervical instability (WAD 3–4) may require neurosurgical intervention to prevent permanent nerve damage and loss of function

  • In intermediate cases (WAD grades 1–3), patients often face challenges in obtaining an accurate diagnosis and appropriate treatment