Posterior bilateral supernumerary atlantoaxial facets: true or false joint?

Area of Science:

• Spinal anatomy and developmental variations.
• Surgical treatment of congenital spinal abnormalities.

Background:

• Accessory joints between the first and second cervical vertebrae (C1-C2) are infrequently documented.
• The developmental origin and functional significance of these joints remain largely unexplored.
• Previous discussions focused on gross anatomy, lacking detailed morphological analysis compared to true synovial joints.

Observation:

• A 17-year-old male presented with spastic ataxia and transient quadriparesis following minor trauma.
• Radiological imaging identified bilateral posterior C1-C2 accessory joints impinging on the cervicomedullary junction.
• Surgical excision of the C1-C2 posterior arches and accessory joints was performed.

Findings:

• Histopathological examination revealed osseous surfaces with articular cartilage but lacked synovial membranes and joint capsules.
• These accessory joints were characterized as dysmorphic and incompletely formed.
• Post-operative fusion using C1-C2 lateral mass screws was successful, with the patient recovering well.

Implications:

• Bilateral posterior accessory C1-C2 joints may arise from genetic aberrations affecting C1 sclerotome segmentation.
• The absence of synovial structures suggests these are not true synovial joints.
• Further research is needed to understand the functional role and clinical relevance of these rare anatomical variations.