Posterior Atlantoaxial Ligament

membrana atlantoaxialis posterior

The posterior atlantoaxial membrane connects the posterior arch of the atlas to the lamina of the axis, forming the posterior boundary of the C1-C2 spinal canal level. It is the analogue of the ligamentum flavum at the atlantoaxial joint.

Region: Neck

Biomechanics

Function & Actions

Provides the posterior spinal canal closure at C1-C2, resists excessive atlantoaxial flexion, and forms the posterior boundary through which posterior C1-C2 approaches pass.

Clinical Relevance

Clinical Notes

The posterior atlantoaxial membrane is divided during posterior C1-C2 surgical approaches (Magerl transarticular screws, Harms C1 lateral mass-C2 pedicle fixation). The vertebral artery loops above the posterior arch of C1 just lateral to the membrane and must be avoided during C1 instrumentation.

Pathology

Common Injuries & Conditions

Vertebral Artery at Posterior Atlantoaxial Membrane

The vertebral artery loops superior to the posterior C1 arch adjacent to the membrane — inadvertent injury during C1 lateral mass screw placement causes catastrophic haemorrhage, requiring awareness of VA anatomy on pre-operative CT angiography.