Anterior Atlantoaxial Ligament
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Description
The strong anterior atlantoaxial ligament is a membrane that connects two vertebrae: it attaches to the bottom edge of the atlas's anterior arch at its upper end, and to the front surface of the axis's body at its lower end[1]. A rounded cord reinforces the central portion of this ligament, extending from the tubercle located on the atlas's anterior arch down to the axis body. This cord represents an upward continuation of the Anterior longitudinal ligament.
Attachments
The atlas vertebra's superior and inferior margins serve as attachment points: the upper border connects to the anterior atlantooccipital membrane (which extends to the occipital bone), while the lower border anchors the anterior atlantoaxial ligament (which connects to the axis vertebra below). The longus capitis muscle lies anterior to this ligamentous structure.[1]
Function
Approximately half of cervical rotation occurs between the first two vertebrae (atlas and axis), primarily around the upward projection of the axis (odontoid process). During this movement, the lateral wall of the atlas moves across the axis's canal, naturally reducing the space between them. The atlas's spinal canal is larger than those of other cervical vertebrae, allowing for rotation and some translational movement without compressing the spinal cord[2].
Clinical Relevance
Atlantoaxial Subluxation may develop without apparent cause, spontaneously or as a consequence of injury/trauma.[2]
Assessment
Sharp Purser Test is a clinical test that assesses for atlantoaxial instability by having the patient flex their head while the examiner presses on their forehead. A positive result indicates instability, and may also be accompanied by a "clunk" sensation or a reduction in symptoms.
Radiological investigations, help diagnose pathologies of the atlanto-axial joint, CT scan of the upper cervical spine that assesses for alar ligament incompetence and subluxation[3].
Treatment
The primary goals in treating atlantoaxial dislocation are to restore proper alignment of the upper cervical spine in the sagittal plane and maintain this corrected position through stabilization. However, there is significant debate in the medical community about how best to achieve these goals. Physicians disagree on when to pursue surgical versus nonsurgical approaches, and among those who favour surgery, there is no consensus on which specific surgical techniques are most effective[4].
Surgical Interventions
Initial Reduction Attempt
This initial step involves carefully applying traction weight starting at 7-8% of body weight and gradually increasing to approximately 7kg, with success rates varying significantly across different studies[4].
Anterior Surgical Approaches
- Transoral odontoidectomy is currently the most accepted treatment for irreducible cases
- Newer minimally invasive options include endoscopic approaches (transnasal, transoral, or retropharyngeal)
- Transoral Atlantoaxial Reduction Plate (TARP) technique offers single-stage treatment
- Anterior transarticular screw fixation provides another option, especially useful in cases with anatomical challenges[4]
Posterior Surgical Methods
- C1-C2 transarticular screw fixation
- C1 lateral mass screw-to-C2 pedicle screw fixation
- C1 lateral mass screw-to-C2 laminar screw fixation[4]
Nonoperative Treatment
Initial treatment for atlantoaxial dislocation typically begins with conservative measures for specific patient groups. The standard nonoperative approach involves placing the patient supine with cervical halter traction while performing active range-of-motion exercises for 24-48 hours. This is followed by ambulatory orthotic immobilization combined with continued range-of-motion exercises until normal movement returns[4].
Certain patients are particularly good candidates for nonoperative management. Children who are diagnosed within 3 weeks of acute transverse ligament disruption can often be treated without surgery, provided they have no neurological deficits. Similarly, patients with Grisel syndrome typically recover on their own, though halter traction may be needed if spontaneous improvement doesn't occur. However, if instability persists, these patients will require posterior arthrodesis for stabilization[4].
For adult patients with symptoms, nonoperative treatment is generally not recommended unless there are specific medical contraindications to surgery[4].
References
- ↑ 1.0 1.1 Henry Gray (1825–1861). Anatomy of the Human Body. 1918. 3a.1.The Cervical Vertebrae.
- ↑ 2.0 2.1 Duke Orthopaedics, Wheeless Textbook of Orthopaedics. Atlantoaxial Subluxation.
- ↑ Henderson, F.C., Rosenbaum, R., Narayanan, M. et al. Atlanto-axial rotary instability (Fielding type 1): characteristic clinical and radiological findings, and treatment outcomes following alignment, fusion, and stabilization. Neurosurg Rev 44, 1553–1568 (2021).
- ↑ 4.0 4.1 4.2 4.3 4.4 4.5 4.6 Yang SY, Boniello AJ, Poorman CE. A review of the diagnosis and treatment of atlantoaxial dislocations. Global Spine J. 2014 Aug;4(3):197-210.