Evolving Concepts of Craniovertebral and Spinal Instability

Area of Science:

• Spinal biomechanics and neurosurgery
• Pathogenesis of craniovertebral and spinal disorders

Background:

• Muscle weakness in the neck and spine leads to instability, a key factor in craniovertebral junction and spinal pathologies.
• Chronic instability causes gradual musculoskeletal and structural spinal changes, including vertical spinal instability and central/axial atlantoaxial instability (CAAD).

Purpose of the Study:

• To elucidate the role of spinal instability in various clinical and pathological events.
• To highlight that secondary alterations are protective responses to instability and are potentially reversible.

Main Methods:

• Review of clinical and pathological events related to spinal instability.
• Analysis of secondary alterations (e.g., Chiari formation, basilar invagination, syringomyelia) as indicators of instability.
• Radiological assessment, noting that instability may not always be evident on dynamic imaging.

Main Results:

• Vertical spinal instability and CAAD can result from spinal segment telescoping.
• Secondary alterations like Chiari formation, basilar invagination, syringomyelia, and Klippel-Feil anomaly are linked to chronic atlantoaxial instability.
• Radiculopathy/myelopathy may originate from vertical spinal instability, spinal degeneration, or ossification of the posterior longitudinal ligament.

Conclusions:

• Secondary spinal alterations are protective indicators of underlying instability, not primary pathologies.
• Surgical stabilization of unstable spinal segments is the fundamental treatment approach.
• Reversal of secondary alterations is possible following successful atlantoaxial stabilization.