Introduction

Atlantoaxial instability (AIA) is a medical condition characterized by excessive movement at the junction between the atlas (C1) and axis (C2), the first two cervical vertebrae. This instability can result from bone or ligament abnormalities, compromising the stability of the upper cervical spine. Due to the complexity of this anatomical region, IAA can lead to neurological disorders when the spinal cord or adjacent nerve roots are affected.

Compared to other cervical segments, the atlantoaxial joint is particularly prone to subluxation, a partial displacement of the joint surfaces. The transverse and alar ligaments play a crucial role in maintaining the stability of this joint. When failure of these structures occurs, it can lead to significant instability, increasing the risk of neurological complications.

The clinical manifestations of IAA vary depending on the severity of the instability and the anatomic structures affected. Patients may experience symptoms such as neck pain, headache, dizziness and, in more severe cases, neurological disorders such as coordination problems, muscle weakness or sensory disturbances. These symptoms often result from compression of the spinal cord or nerve roots by unstable structures.

It is important to note that instability of the upper cervical spine can compromise the vascular structures, particularly the vertebral arteries, which pass through this region. Impaired blood flow can lead to serious complications, including stroke. In such circumstances, the use of spinal manipulation is contraindicated, as it could worsen instability and potentially cause neurovascular damage.

The diagnosis of IAA is based on imaging tests such as MRI or CT scan, allowing the bone structure and ligaments to be evaluated and any signs of instability to be identified. Treatment for IAA depends on the severity of the condition and may include conservative measures such as rest, physical therapy, and the use of neck braces to stabilize the area. In severe cases, surgery may be considered to stabilize the joint and relieve compression of the nerve structures.

In conclusion, atlantoaxial instability is a complex condition that can have serious consequences on neurovascular health. Understanding this pathology is essential for early diagnosis and appropriate treatment, in order to minimize potential complications and improve the quality of life of patients affected by this condition.

Causes

  1. Congenital anomalies: Some individuals are born with structural anomalies at the atlas (C1) and axis (C2), which can lead to atlantoaxial instability.
  2. Trauma: Injuries to the neck, particularly those affecting the atlas and axis region, can cause atlantoaxial instability. This can result from car accidents, falls, or other types of trauma.
  3. Inflammatory Diseases: Inflammatory conditions such as rheumatoid arthritis can affect the cervical joints and cause atlantoaxial instability.
  4. Down syndrome: People with Down syndrome sometimes have atlantoaxial instability due to certain anatomical features.
  5. Infections: Infections, although less common, can sometimes lead to atlantoaxial instability.
  6. Tumors: Tumors in the cervical spine can disrupt the stability of the vertebrae.
https://youtube.com/watch?v=41HHZpNhqOo%3Ffeature%3Doembed%26enablejsapi%3D1

Symptoms

Symptoms of atlantoaxial instability can vary depending on the severity and underlying cause. Here are some potential symptoms:

  1. Neck pain: Persistent pain in the neck area may be a symptom of atlantoaxial instability.
  2. Headaches: Frequent or severe headaches may be associated with this condition.
  3. Neck Stiffness: A feeling of stiffness or restricted movement in the neck may occur.
  4. Numbness or tingling: Abnormal sensations in the arms, hands, or other parts of the body may occur due to nerve compression.
  5. Muscle weakness: Severe atlantoaxial instability can lead to muscle weakness, particularly in the arms.
  6. Balance Problems: Some patients may experience balance or coordination problems due to cervical disruption.
  7. Neurological disorders: In severe cases, atlantoaxial instability can lead to neurological disorders such as vision problems, difficulty swallowing, and speech problems.

It is important to note that all of these symptoms can also be associated with other medical conditions, and only a healthcare professional can make an accurate diagnosis.

Pathophysiology

  1. Normal Anatomy of the Atlanto-Axial:
    • The first cervical vertebra (C1 or atlas) and the second cervical vertebra (C2 or axis) form the atlantoaxial joint. This joint allows the head to rotate from side to side.
  2. Ligaments and Stability:
    • Ligaments surround and stabilize the atlantoaxial joint. These ligaments, such as the transverse atlas ligament and the alar ligament, play a crucial role in maintaining the stability of this region.
  3. Trauma or Congenital Malformation:
    • Atlantoaxial instability can result from trauma, such as a neck injury, or from a congenital malformation that weakens ligaments or alters the shape of the vertebrae.
  4. Weakening of Ligaments:
    • Due to trauma or malformation, the ligaments surrounding the atlantoaxial joint can weaken, lose elasticity or suffer damage. This can compromise the normal stability of the joint.
  5. Excessive Movement:
    • Weakening of the ligaments can lead to excessive or abnormal movement between the atlas and the axis. This movement can manifest itself as excessive rotation of the head, particularly when the neck is stressed.
  6. Compression of Nervous Structures:
    • Atlantoaxial instability can compress surrounding nerve structures, such as the spinal cord or cervical nerve roots. This can lead to symptoms such as neck pain, headaches, numbness, or weakness in the arms.
  7. Neurological Symptoms:
    • Neurological symptoms may vary depending on the severity of the instability and compression of the nerve structures. In some cases, more serious symptoms such as coordination problems, speech problems, or difficulty walking may occur.
  8. Diagnostic:
    • The diagnosis of atlantoaxial instability relies on imaging tests, such as X-rays, MRIs or CT scans, to evaluate the structure of the vertebrae and ligaments.
  9. Treatment:
    • Treatment for atlantoaxial instability depends on the underlying cause and severity of symptoms. Approaches may include conservative management with supportive devices such as cervical collars, muscle strengthening exercises, or in some more severe cases, surgery to stabilize the area.

Spencer’s rule


The atlantoaxial segment is made up of the atlas (C1) and the axis (C2) and forms a complex transitional structure connecting the occiput and the cervical spine.

The functional result of this joint is twofold: providing support for the occiput and providing the greatest possible range of motion and flexibility while maintaining stability.

Instability in this joint is usually congenital, but in adults it can result from an acute traumatic event or degenerative disease.

Atlantoaxial instability can be classified into three generalized categories: inflammatory, congenital, and traumatic.

“Spence’s Rule” classically determines the stability of C1 fractures by measuring the lateral spillover of C1 lateral masses onto C2 when examining an AP radiograph. If the sum of the two lateral masses of C1 over C2 is greater than 7 mm, the fracture is considered unstable. This measurement tool is also typically used to evaluate computed tomography (CT scan) images.

Treatment for atlantoaxial instability varies widely, and intervention is generally tailored to patients on an individualized basis. Asymptomatic patients can be monitored over time with dynamic images and MRI to track disease progression.

The prognosis in symptomatic patients treated early is good. Posterior spinal fusion can help restore function and reverse symptoms such as pain and myelopathy.

How to diagnose atlantoaxial instability?

Transverse Ligament Stress Test

  • Atlantoaxial instability and rupture of the transverse ligament.
  • Patient seated with head at approximately 20 degrees of flexion.
  • Push the patient’s forehead back while stabilizing the C2 process.
  • Excessive posterior sliding or pain relief with a sliding motion is a positive test

Alar Ligament Stress Test

  • Rupture of the alar ligament
  • Patient sits with head at approximately 20 degrees of flexion.
  • Palpate C2 with one hand and with the other move the patient’s head into lateral flexion.
  • You should feel C2 kicker in the hand opposite the direction you are flexing your head laterally.
  • Absence of sensation of movement of the C2 spinous process indicates a positive test

References

  1. Goel A. Indicators of atlantoaxial  instability . J Craniovertebr Junction Spine. 2021 Apr-Jun;12(2):103-106. [ PMC free article ] [ PubMed ]2.
  2. Scholz C, Klingler JH, Scheiwe C, Naseri Y, Masalha W, Hubbe U. Atlantoaxial  Instability  in Patients Older Than 70 Years: What Is the Outcome When Further Conservative Treatment Is Not an Option? J Neurol Surg A Cent Eur Neurosurg. 2018 Sep;79(5):372-379. [ PubMed ]3.
  3. Cummings KR, Vilaplana Grosso F, Moore GE, Rochat M, Thomovsky SA, Bentley RT. Radiographic indices for the diagnosis of atlantoaxial  instability  in toy breed dogs [corrected]. Vet Radiol Ultrasound. 2018 Nov;59(6):667-676. [ PubMed ]4.
  4. Kothe R. [Rheumatoid  instability  in the cervical spine: Diagnostic and therapeutic strategies]. Orthopad. 2018 Jun;47(6):489-495. [ PubMed ]5.
  5. Yang SY, Boniello AJ, Poorman CE, Chang AL, Wang S, Passias PG. A review of the diagnosis and treatment of atlantoaxial dislocations. Global Spine J. 2014 Aug;4(3):197-210. [ PMC free article ] [ PubMed ]6.
  6. Macovei LA, Rezuş E. CERVICAL SPINE LESIONS IN RHEUMATOID ARTHRITIS PATIENTS. Rev Med Chir Soc Med Nat Iasi. 2016 Jan-Mar;120(1):70-6. [ PubMed ]7.
  7. Lyons C, Ross M, Elliott R, Tall M. Atlantoaxial  Instability  in a Patient with Neck Pain and Ankylosing Spondylitis. Mil Med. 2018 Sep 01;183(9-10):e654-e657. [ PubMed ]8.
  8. Goyal N, Bali S, Ahuja K, Chaudhary S, Barik S, Kandwal P. Posterior Arthrodesis of Atlantoaxial Joint in Congenital Atlantoaxial  Instability  Under 5 Years of Age: A Systematic Review. J Pediatr Neurosci. 2021 Apr-Jun;16(2):97-105. [ PMC free article ] [ PubMed ]9.
  9. Abou-Madawi AM, Ali SH, Alaswad M, Elkazaz MK, Abdelaziz MA, AlQazzaz MY, Al-Shatoury HA. Feasibility and Safety of Goel-Harms Posterior C1-C2 Fusion in the Management of Pediatric Reducible Atlantoaxial  Instability . World Neurosurg. 2021 Nov;155:e592-e599. [ PubMed ]10.
  10. Burkhardt BW, Podolski W, Pitzen TR, Ruf M. The Feasibility of C1-C2 Screw-rod Fixation in the Children 5 Years of Age and Younger. J Pediatr Orthop. 2021 Sep 01;41(8):e651-e658. [ PubMed ]11.
  11. Raut S, Kundnani VG, Meena MK, Patel JY, Asati S, Patel A. Anthropometric evaluation for surgical feasibility of C1-C2 transarticular screw stabilization in Indian population. J Craniovertebr Junction Spine. 2021 Apr-Jun;12(2):129-135. [ PMC free article ] [ PubMed ]12.
  12. Su ML, Liu ZH, Tu PH, Huang YC. Dynamic cervical flexion/extension atlantodental interval and functional outcome of the Harms technique for posterior C1/2 fixation: A retrospective analysis of 16 atlantoaxial subluxation cases in a tertiary medical center. Neurosurgery. 2022 Feb;68(2):168-174. [ PubMed ]13.
  13. Kleinstück FS, Fekete TF, Loibl M, Jeszenszky D, Haschtmann D, Porchet F, Mannion AF. Patient-rated outcome after atlantoaxial (C1-C2) fusion: more than a decade of evaluation of 2-year outcomes in 126 patients. Eur Spine J. 2021 Dec;30(12):3620-3630. [ PubMed ]14.
  14. Tatter C, Fletcher-Sandersjöö A, Persson O, Burström G, Edström E, Elmi-Terander A. Fluoroscopy-Assisted C1-C2 Posterior Fixation for Atlantoaxial Instability  : A Single-Center Case Series of 78 Patients. Medicine (Kaunas). 2022 Jan 12;58(1) [ PMC free article ] [ PubMed ]15.
  15. Malikov A, Secen AE, Divanlioglu D, Gunerhan G, Ocal O, Gunduz UK. The Feasibility of Creating Image-Based Patient-Specific Drill Guides for the Atlantoaxial Instabilities Using Open-Source CAD Software and Desktop 3D Printers. World Neurosurg. 2022 Jul;163:e377-e383. [ PubMed ]16.
  16. Jannelli G, Moiraghi A, Paun L, Cuvinciuc V, Bartoli A, Tessitore E. Atlantoaxial posterior screw fixation using intra-operative spinal navigation with three-dimensional isocentric C-arm fluoroscopy. Int Orthop. 2022 Feb;46(2):321-329. [ PubMed ]17.
  17. Du JY, Aichmair A, Kueper J, Wright T, Lebl DR. Biomechanical analysis of screw constructs for atlantoaxial fixation in cadaver: a systematic review and meta-analysis. J Neurosurg Spine. 2015 Feb;22(2):151-61. [ PubMed ]18.
  18. Zileli M, Akıntürk N. Complications of occipitocervical fixation: retrospective review of 128 patients with 5-year mean follow-up. Eur Spine J. 2022 Feb;31(2):311-326. [ PubMed ]19.
  19. Joaquim AF, Tedeschi H, Chandra PS. Controversies in the surgical management of congenital craniocervical junction disorders – A critical review. Neurol India. 2018 Jul-Aug;66(4):1003-1015. [ PubMed ]20.
  20. Robinson LC, Anderson RCE, Brockmeyer DL, Torok MR, Hankinson TC., Pediatric Craniocervical Society. Comparison of Fusion Rates Based on Graft Material Following Occipitocervical and Atlantoaxial Arthrodesis in Adults and Children. Opera Neurosurg (Hagerstown). 2018 Nov 01;15(5):530-537. [ PMC free article ] [ PubMed ]

RELATED ARTICLESMORE FROM AUTHOR